Selina Concise Solutions for ICSE Class 6 Physics Chapter 2 Physical Quantities and Measurement

Synposis

1. The observation of a phenomenon is made possible by using the five senses: sight, smell, touch, hearing and taste.
2. Our senses are not always reliable. They are subjective.
3. Sometimes it is necessary to make an exact measurement.
4. Physics is a science of measurement.
5. We use instruments to get an exact measurement.
6. Four basic measurements in our daily life are: measurement of length, measurement of mass, measurement of time, and measurement of temperature.
7. Measurement is basically a process of comparison of the given quantity with a standard unit.
8. For measuring a quantity we need a unit, and then we find the number of times that unit is contained in that quantity.
9. The unit selected for measurement should be of a convenient size and it must not change with place or time.
10. The distance between two fixed points is called length.
11. The S.I. unit of length is metre (m). Its multiple is kilometre (km), where 1 km = 1000 m. Its sub multiples are centimetre (cm) and millimetre (mm), where 1 cm = 10^-2 m and 1 mm = 10^-3 m.
12. The FPS unit of length is foot (ft) and its sub multiple is inch where 1 ft = 12 inch and 1 ft = 30.48 cm.
13. The most common instruments used to measure length are the metre ruler and the measuring tape which are marked in cm and mm.
14. To measure a length accurately with a metre ruler, the scale should be placed with its markings close to the object and parallel to its length. The eye is kept in front of and in line with the reading to be taken.
15. The quantity of matter contained in a body is called its mass.
16. The S.I. unit of mass is kilogram (kg). Its multiples are quintal and metric tonne. 1 quintal = 100 kg and 1 metric tonne = 10 quintal = 1000 kg. Its sub multiples are gram (g) and milligram (mg) where 1 g = 10^-3 kg and 1 mg = 10^-6 kg.
17. The FPS unit of mass is pound (lb) where 1 lb = 453.59 g.
18. Mass of a body is measured by using a beam balance or an electronic balance.
19. The interval between two instances or events is called time.
20. The S.I. unit of time is second (s), 1 s = 1 / 86400 of a mean solar day. The C.G.S. and F.P.S. unit of time is also second (s).
21. The multiple unit of time are minute (min), hour (h), day and year where 1 min = 60 s, 1 h = 3600 s, 1 day = 86400 s and 1 year = 3.15 × 10⁷ s.
22. The time at any instant is recorded by a pendulum clock or watch and the time interval of an event is measured by using a stop watch or a stop clock.
23. The temperature is the measure of degree of hotness or coldness of a body.
24. The S.I. unit of temperature is kelvin (K), but the common unit of temperature is degree Celsius (°C) and degree fahrenheit (°F).
25. Doctors use a clinical thermometer to measure the patient’s body temperature.
26. The normal temperature of a human body is 37°C or 98.6°F.
27. The total surface occupied by an object is called its area. Area is expressed as the product of measured length of two sides.
28. The S.I. unit of area is square metre (m²).
29. One square metre is the area of a square of each side one metre.
30. The bigger (or multiple) units of area are dam², hectare and square kilometre (km²), where 1 dam² = 100 m², 1 hectare = 10⁴ m² and 1 km² = 10⁶ m².
31. The smaller (or sub multiple) units of area are cm² and mm² where 1 cm² = 10^-4 m² and 1 mm² = 10^-6 m².

Test yourself

A. Objective Questions

1. Write true or false for each statement

(a) S.I. unit of temperature is fahrenheit.
Answer: False
The S.I. system recognizes Kelvin as the primary unit for scientific temperature measurements. Fahrenheit is a different scale commonly used for weather and body temperature in certain countries.
Teacher's Tip: Remember "K" for Kelvin, the scientific King of temperature!
Exam Tip: Always write the symbol for Kelvin as a capital K without the degree symbol.

(b) Every measurement involves two things - a number and a unit
Answer: True
A number tells us the magnitude, while the unit tells us what standard we are comparing it against. Without both parts, a measurement like "5" would be meaningless because we wouldn't know if it meant 5 meters or 5 kilograms.
Teacher's Tip: Think of measurement as a name: the number is the first name and the unit is the last name.
Exam Tip: To get full marks, always include both the numerical value and the correct unit in your final answers.

(c) Mass is the measure of quantity of matter.
Answer: True
Mass represents the total amount of particles or "stuff" that makes up an object. This value remains constant no matter where the object is located in the universe.
Teacher's Tip: Mass is "Matter" - they both start with "M"!
Exam Tip: Do not confuse mass with weight; mass stays the same everywhere, but weight changes with gravity.

(d) The S.I. unit of time is hour.
Answer: False
In the International System of Units, the second is used as the base unit for measuring time. Hours and minutes are considered multiples of this fundamental unit.
Teacher's Tip: The "S" in S.I. units for time stands for Second.
Exam Tip: Remember that 1 hour = 3600 seconds when performing unit conversions.

(e) The area can be expressed as the product of length of two sides.
Answer: Tme
Area measures the extent of a surface and is calculated by multiplying two linear dimensions together. For a simple rectangle, this is typically the length multiplied by the width.
Teacher's Tip: Area is "2D", so you always multiply 2 numbers.
Exam Tip: Units for area must always be squared, such as cm² or m².

2. Fill in the blanks

(a) The S.I. unit of length is metre of time is second of mass is kilogram.
Answer: metre, second, kilogram.
These three units are the building blocks of the metric system used by scientists worldwide. Using these standard units ensures that measurements are consistent and easy to communicate.
Teacher's Tip: Use the acronym "MKS" to remember Metre, Kilogram, and Second.
Exam Tip: Ensure you spell "metre" and "kilogram" correctly as per the S.I. convention to avoid losing marks.

(b) °C is the unit of temperature.
Answer: temperature.
The Celsius scale is widely used around the world for everyday temperature readings like weather and cooking. It is based on the freezing and boiling points of pure water.
Teacher's Tip: Think of "C" for Celsius and "Cold" or "Cooking".
Exam Tip: Always include the degree symbol (°) before the C when writing Celsius.

(c) 1 metric tonne = 1000 kg
Answer: 1000.
A metric tonne is a very large unit of mass used for heavy items like vehicles or industrial cargo. It is exactly equal to ten quintals or one thousand kilograms.
Teacher's Tip: "Tonne" sounds like "Ton" of weight; it’s the biggest mass unit you’ll likely use.
Exam Tip: Memorize the conversion: 1 Tonne = 10 Quintals = 1000 kg for multi-step problems.

(d) The zero mark in Celsius thermometer is the melting point of ice
Answer: ice.
On the Celsius scale, 0°C is specifically chosen to represent the temperature at which ice turns into water. This provides a clear and repeatable reference point for calibrating thermometers.
Teacher's Tip: Zero is "Freezing" - think of an ice cube!
Exam Tip: Be ready to identify 100°C as the steam point (boiling point of water) as well.

(e) The thermometer used to measure the human body temperature is called the clinical thermometer.
Answer: clinical.
A clinical thermometer is designed with a narrow range and a special kink to measure body heat accurately. It helps doctors determine if a person has a fever by comparing their temperature to the healthy average.
Teacher's Tip: "Clinical" is related to a clinic where doctors work.
Exam Tip: Mention the "kink" or "constriction" if asked about the special feature of this thermometer.

(f) The normal temperature of human body is 37 °C or 98.6 °F.
Answer: 37, 98.6.
This is the standard internal temperature for a healthy human being. If a reading is significantly higher or lower, it usually indicates that the person is unwell.
Teacher's Tip: 37 is the "Lucky Number" for human health in Celsius!
Exam Tip: Know both values (Celsius and Fahrenheit) as the question might ask for either one.

(g) The mass of an object is measured with the help of a beam balance.
Answer: beam balance.
A beam balance works by comparing the unknown mass of an object on one pan with known standard weights on the other. When the beam is perfectly horizontal, the masses on both sides are equal.
Teacher's Tip: Think of a see-saw that has to stay perfectly level.
Exam Tip: Identify the "standard weights" as the tool used for comparison in a beam balance.

3. Match the following columns

Column A
(a) Length of a housing plot
(b) Breadth of a book
(c) Mass of an apple
(d) Period of time for study
(e) Temperature of a body
(f) Surface area of a leaf

Column B
(i) Clock
(ii) Beam balance
(iii) Thermometer
(iv) Measuring tape
(v) Graph paper
(vi) Metre ruler
Answer:
(a) Length of a housing plot - (iv) Measuring tape
(b) Breadth of a book - (vi) Metre ruler
(c) Mass of an apple - (ii) Beam balance
(d) Period of time for study - (i) Clock
(e) Temperature of a body - (iii) Thermometer
(f) Surface area of a leaf - (v) Graph paper
Each physical quantity is measured using a specific instrument designed for that particular purpose and scale. For irregular shapes like a leaf, we use graph paper to estimate the area by counting the squares it covers.
Teacher's Tip: Just remember to pair the "Measurement" with its "Instrument" - the tape is for distance, the balance is for mass, and the clock is for time.
Exam Tip: In matching questions, double-check that you haven't used the same option twice to ensure you get full marks for all parts.

4. Select the correct alternative

(a) The symbol of degree Celsius is
1.°C
2. °F
3. K
4.°K
Answer: 1. °C
The symbol °C specifically denotes the Celsius scale. It consists of a small circle representing "degree" followed by a capital letter C.
Teacher's Tip: The circle must always come before the letter.
Exam Tip: Remember that Kelvin (K) never uses the degree symbol, while Celsius and Fahrenheit always do.

(b) 10 mm is equal to
1. 1cm
2. 1m
3. 10dm
4. 10cm
Answer: 1. 1cm
The metric system is based on powers of ten, making conversions very simple. There are exactly 10 millimeters inside a single centimeter.
Teacher's Tip: Look at a standard ruler; the tiny lines are mm, and every ten of them make a cm.
Exam Tip: Practice the "King Henry" mnemonic (Kilo, Hecto, Deca, Base, Deci, Centi, Milli) for quick conversions.

(c) The amount of surface occupied by an object is called its:
1. volume
2. area
3. mass
4. length
Answer: 2. area
Area specifically refers to the two-dimensional space that a flat surface covers. Volume, on the other hand, measures the three-dimensional space inside an object.
Teacher's Tip: Area is the "Floor Space", Volume is the "Room Space".
Exam Tip: If the question mentions "surface," the answer is almost always "area."

(d) A metre ruler is graduated in:
1. m
2. cm
3. mm
4. km
Answer: 3. mm (Note: While it shows cm, the smallest markings are mm).
"Graduated" means the marks or divisions printed on the scale. Most standard rulers have small millimetre marks to allow for very precise measurements.
Teacher's Tip: Graduation is just another word for the "Little Lines" on a scale.
Exam Tip: Check the smallest division of any instrument to find its least count.

(e) A thermometer is graduated in:
1. kelvin
2. °C
3. g
4. cm
Answer: 2. °C
Common thermometers used in schools and homes are typically marked with the Celsius scale. This allows us to read temperatures relative to the freezing and boiling points of water easily.
Teacher's Tip: Graduations on a thermometer tell us the "Hotness" level.
Exam Tip: Always specify the unit being used on a scale when recording a measurement.

B. Short/Long Answer Questions

Question 1: What is measurement? How is a measurement expressed?
Answer: Measurement is a comparison of an unknown quantity with a known fixed quantity of the same kind. The value obtained on measuring a quantity is called its magnitude. The magnitude of a quantity is expressed as numbers in its unit.
When we measure something, we are basically checking how many "standard units" fit into the object we are measuring. For instance, saying a table is "2 metres" long means it is twice as long as the standard 1-metre rod.
Teacher's Tip: Measurement = Number × Unit.
Exam Tip: Use a simple example like "5 kg" to show the number (magnitude) and the unit clearly.

Question 2: State two characteristics of a unit.
Answer: Two characteristics of a unit are:
1. It should be of convenient size.
2. It must be universally accepted, i. e. its value must remain same at all places and at all times.
A good unit must be practical to use for common measurements and must be the same for everyone, everywhere. This prevent confusion in trade, science, and daily communication between different regions.
Teacher's Tip: A unit must be "Handy" and "Global".
Exam Tip: Mentioning "Universal Acceptance" is the most important point for scoring well here.

Question 3: Name four basic measurements in our daily life.
Answer: In our daily life we measure the following four basic physical quantities.
1. Length
2. Mass
3. time
4. Temperature
These four quantities help us describe physical objects and events accurately. Whether we are measuring ingredients for a cake or the distance to school, we use these fundamental concepts.
Teacher's Tip: Just remember: How long, how heavy, how hot, and how fast!
Exam Tip: List these clearly in a numbered list to make them easy for the examiner to see.

Question 4: What are the S.I. units of 1. mass 2. length 3. time and 4. temperature. Write their names and symbols.
Answer: S.I. units are as follows
Quantity --- S.I. unit --- Symbol of S.I. unit
(i) Length --- metre --- m
(ii) Mass --- kilogram --- kg
(iii) Time --- second --- s.
(iv) Temperature --- kelvin --- k
The S.I. units provide a common language for measurements across the globe. Standardized symbols prevent any language barriers when scientists share their data.
Teacher's Tip: Symbols don't have periods (s not s.) and aren't plural (kg not kgs).
Exam Tip: Pay close attention to capitalization; Kelvin is K (capital) while metre is m (lowercase).

Question 5: Define one metre, the S.I. unit of length. State its one multiple and one sub multiple.
Answer: One metre is defined as the distance travelled by light in air in 1/299,792,458 of a second. Multiple of metre = Kilometre; Submultiple of metre = Centimetre.
The official definition of a metre is based on the speed of light because light travels at a constant speed that never changes. This ensures that the standard metre is perfectly accurate for everyone.
Teacher's Tip: A multiple makes a unit bigger (km), and a submultiple makes it smaller (cm).
Exam Tip: Include the exact fraction (1/299,792,458) to demonstrate precise knowledge of the definition.

Question 6: Convert the following quantities as indicated (a) 12 inch = ft (b) 1 ft = cm (c) 20 cm = m (d) 4.2 m = cm (e) 0.2 km = m (f) 0.2 cm = mm (g) 1 yard = m
Answer:
(a) 12 inch = 1 ft
(b) 1ft = 30.48cm
(c) 100 cm = 1m \therefore 1 cm = 1/100 m \therefore 20 cm = 1/100 × 20 m = 0.2 m
(d) 1 m = 100 cm \therefore 4.2 m = 100 × 4.2 cm = 420 cm
(e) 1 km = 1000 m \therefore 0.2 km = 1000 × 0.2 m = 200 m
(f) 1 cm = 10 mm \therefore 0.2 cm = 10 × 0.2 mm = 2 mm
(g) 1 yard = 0.91 m
Converting units allows us to switch between different measurement systems or adjust the scale of our numbers. Multiplication is used when going from large units to small ones, and division is used for small to large.
Teacher's Tip: Big unit to Small unit? Multiply! Small unit to Big unit? Divide!
Exam Tip: Show your steps and the conversion factor (like 100 ×) to ensure you get step-marks even if the final result is wrong.

Question 7: (a) Describe in steps how would you measure the length of a pencil using a metre rule. Draw a diagram if necessary.
Answer: To measure the length of a pencil using a metre rule, place metre rule with its marking close to the object. Let PQ be a pencil. The end P of the pencil coincides with the zero mark on the ruler. The end Q of the pencil is read by keeping the eye at the position ‘B’ vertically above the end Q. So the length of pencil is 4.3 cm.
Accurate measurement requires aligning the object perfectly with the start of the scale. It is also critical to look straight down at the markings to avoid an error called parallax.
Teacher's Tip: Always "Zero" your scale before you start reading.
Exam Tip: When describing steps, use clear terms like "coincides" and "vertically above."

Question 7: (b) Explain with an example how you will use the metre ruler in part (a) if the ends of ruler are broken.
Answer: The ends of the ruler get damaged with use and its zero mark may not be visible. To measure the length of an object with such a ruler, the object is placed close to a specific markings on the ruler and positions of both ends of the object are read on the ruler. The difference of the two readings gives the length of the object. In fig. the reading on ruler at the end X is 1.0 cm and at the end Y is 4.3 cm. So the length of the rod XY is 4.3 - 1.0 = 3.3 cm.
Even if a ruler is damaged, you can still measure accurately by starting at a different whole number like 1.0 cm. You simply subtract the starting number from the final reading to find the true length.
Teacher's Tip: Just think: Final Reading - Initial Reading = Total Length.
Exam Tip: If you use this method in an exam, clearly state both the initial and final readings you used.

Question 8: Name the device which you will use to measure the perimeter of your play ground. Describe in steps how you will use it.
Answer: We will use a measuring tape to measure the perimeter of our playground. To measure the length of playground the tape is spread along the length of the curved area.
Measuring tapes are flexible, which makes them much better than wooden rulers for measuring long or curved boundaries. You simply stretch the tape along the perimeter and read the final mark.
Teacher's Tip: Rulers are for desks, Tapes are for playgrounds!
Exam Tip: Mention that the tape must be kept "taut" (pulled straight) for the most accurate measurement.

Question 9: The diagram below shows a stick placed along a metre RULER. The length of the stick is measured keeping the eye at positions A, B and C. (a) Write the length if stick PQ as observed, for each position of the eye. Are they all same? (b) Which is the correct position of the eye? Write the correct length of the stick.
Answer: (a) Length of stick PQ from: Position A = 3.4 cm, Position B = 3.2cm, Position C = 3.00 cm. No they are not same. (b) ‘B’ is the correct position of the eye. Correct length of the stick PQ = 3.2cm.
This experiment demonstrates parallax error, which happens when you look at a scale from an angle. Only by looking directly from above (Position B) can you get the true reading of the object's length.
Teacher's Tip: Always look "Straight Down" to get it right.
Exam Tip: If you are asked why the values are different, use the term "Parallax Error" in your answer.

Question 10: Define mass. State its (1) S.I. (2) C.GS and (3) EP.S. units. How are they related ?
Answer: The mass of a body is the quantity of matter contained in it. The S.I. unit of mass is kilogram. In short form, it is written as kg. In C.GS. system, the unit of mass is gram, (symbol g). In F.P.S. system, the unit of mass is pound (symbol lb)
Mass measures the physical substance inside an object and doesn't change based on location. Different systems use different base units, but they can all be converted into one another using fixed formulas.
Teacher's Tip: Mass = How much "stuff" is inside.
Exam Tip: Be sure to learn the symbols: kg, g, and lb.

Question 11: Convert the following quantities as indicated: (a) 2500 kg = metric tonne. (b) 150 kg = quintal (c) 10 lb = kg (d) 250 g = kg (e) 0.01 kg = g (f) 5 mg = kg
Answer:
(a) 2500 kg = 2.5 metric tonne. (As 1000 kg = 1 metric tonne)
(b) 150 kg = 1.5 quintal (As 100 kg = 1 quintal)
(c) 10 lb = 4.5359 kg (As 1 lb = 0.45359 kg)
(d) 2500 g = 2.5 kg (As 1000 g = 1 kg)
(e) 0.01 kg = 10 g (As 1 kg = 1000 g)
(f) 5 mg = 5 × 10^-6 kg (As 1 kg = 1000000 mg)
Unit conversion requires knowing the exact ratio between two units. Once you know that 1000 grams equals one kilogram, you just need to multiply or divide based on which unit you are starting with.
Teacher's Tip: Kilo means 1000. So 1 kg is 1000 grams.
Exam Tip: Show the conversion factor in brackets (e.g., [As 1 kg = 1000 g]) to get full marks for your working steps.

Question 12: Name the instrument which is commonly used to measure the mass of a body. State how is it used ?
Answer: Instrument commonly used to measure the mass of a body, is the beam balance. When we hold up the balance, we observe that when there is nothing on either pan, the beam is horizontal. The body whose mass is to be measured is placed on the left pan. The standard weight are put on the right pan. They are so adjusted that the beam is again horizontal on holding the balance up. The total of the standard weights gives the mass of the given body.
A beam balance relies on the principle of equilibrium. By balancing the unknown object against known "standard weights," we can find the exact mass of that object.
Teacher's Tip: It's like a scientific see-saw; both sides must match perfectly.
Exam Tip: Mention that the beam must be "horizontal" as this indicates the two sides are perfectly balanced.

Question 13: Define one kilogram, the S.I. unit of mass. How is it related to (i) quintal (ii) metric tonne and (iii) gram.
Answer: The mass of 1 litre of water at 4 °C is taken as 1 kilogram. 1 quintal = 100 kg; 1 metric ton = 10 quintal = 1000 kg.
The kilogram was originally based on the mass of a specific volume of water because water is easily available for comparison. Today, it is part of a larger decimal system where every unit is a multiple of 10 or 100 from the next.
Teacher's Tip: 1 Litre of water = 1 Kilogram. It's a very easy way to visualize mass!
Exam Tip: If asked about grams, remember that 1 gram = 1/1000 of a kilogram.

Question 14: Name and define the S.I. unit of time. How is it related to (i) minute (ii) hour, (iii) day and (iv) year ?
Answer: The S.I. unit of time is second. In short form we write it as ‘ S ’. One second is the time interval between the two consecutive ticks that you hear from pendulum wall clock. 1 min = 60 s; 1 h = 60 min. = 3600 s.; 1 day = 24 h = 86400 s.; 1 year = 365 days = 3.15 × 10⁷ s.
Time units are based on the movement of the Earth relative to the sun. While seconds are small, they build up into minutes, hours, and years that help us track our lives and the planet's orbit.
Teacher's Tip: 3600 is the magic number for seconds in one hour (60 × 60).
Exam Tip: Don't forget the symbol for second is just a lowercase 's'.

Question 15: Name two devices used to measure the short time interval of an event.
Answer: Two devices used to measure the time interval of an event are: 1. StopWatch 2. Stop Clock
Standard clocks show the time of day, but stopwatches are designed to measure exactly how long a specific action takes. They are widely used in sports and scientific experiments where every split-second matters.
Teacher's Tip: A stopwatch "stops" the time so you can read the duration easily.
Exam Tip: These are used for "intervals," not for telling the time of day.

Question 16: Express in second: 1. 3 minute 15 second and 2. 5 hour 2 minute 5 second.
Answer:
1. 3 minute = 3 × 60 = 180 seconds. 3 minutes 15 second = 180 + 15 = 195 seconds.
2. 1 hour = 3600 second. 5 hour = 3600 × 5 = 18000 second. 2 minutes = 2 × 60 = 120 second. Total = 18000 + 120 + 5 = 18125 seconds.
To find total seconds, you must convert every larger unit (hours and minutes) separately and then add them all together at the end. Always use the standard conversion factors: 60 for minutes and 3600 for hours.
Teacher's Tip: Think of it like changing big bills into small coins; you need to know the exchange rate for each.
Exam Tip: Always show your addition step (18000 + 120 + 5) so you don't lose marks for a simple math error.

Question 17: What does the temperature measure ?
Answer: Temperature measures the degree of coldness and hotness of a body.
It tells us how much thermal energy an object contains. When particles inside an object move faster, the temperature reading goes up.
Teacher's Tip: Temperature is just the "Energy Level" of heat.
Exam Tip: Use the exact phrase "degree of hotness or coldness" for a perfect definition.

Question 18: Name the 1. S.I. unit and 2. one common unit of temperature. Write their symbols also.
Answer: The S.I. unit of temperature is kelvin (symbol K). Common unit of temperature is degree centigrade (symbol °C)
Scientists use Kelvin because it starts at "absolute zero," the point where all motion stops. In everyday life, we use Celsius (centigrade) because it is conveniently based on water's properties.
Teacher's Tip: Symbols for units named after people (like Kelvin) are usually capital letters.
Exam Tip: Make sure to include both the name and the symbol when the question asks for both.

Question 19: Name the instrument used for measuring of the temperature of a person. Draw its labelled neat diagram.
Answer: The temperature is measured with a thermometer.
Thermometers use the expansion of liquids, usually mercury or alcohol, to show temperature changes on a scale. As the liquid gets warmer, it takes up more space and rises up the thin tube.
Teacher's Tip: Thermo = Heat; Meter = Measure. Heat-measurer!
Exam Tip: When drawing a diagram, clearly label parts like the "bulb," "stem," and "capillary tube."

Question 20: Write the temperature of (i) melting ice (ii) boiling water.
Answer: The temperature of 1. melting ice = 0°C and 2. boiling water = 100°C.
These two temperatures are the standard anchor points for the Celsius scale. They occur consistently as long as the water is pure and the air pressure is normal.
Teacher's Tip: Remember the "100-degree difference" between freezing and boiling.
Exam Tip: If the question doesn't specify a scale, always provide the answer in Celsius as it is the most common.

Question 21: What is a clinical thermometer? State its special feature. Draw a labelled neat diagram of a clinical thermometer showing the range of temperature marked on it.
Answer: Doctors use a special thermometer called the clinical thermometer for measuring the temperature of the patient’s body. This thermometer has the markings from 35°C to 42°C. It has a slight bend or kink in the stem just above the bulb. This kink is called the constriction. This constriction prevents the mercury from falling back all by itself. The temperature of a healthy person is 37°C. This temperature is marked by a red arrow.
The special "kink" is what makes this thermometer different from ones used in labs. It "locks" the mercury at the highest temperature reached, giving the doctor time to read it after taking it out of the patient's mouth.
Teacher's Tip: The kink is like a "One-Way Gate" for mercury.
Exam Tip: Always mention the range (35°C to 42°C) when describing a clinical thermometer.

Question 22: What is the normal temperature of the human body? How is it indicated in a clinical thermometer?
Answer: Normal temperature of a human body is 37°C or 98.6°F. To measure the temperature of a patient’s body, its bulb is kept either below the tongue or under the arm’s pit of the patient for about a minute. Then the thermometer is taken out and its reading is noted. When the temperature of patient’s body is above 37°C, he is said to suffer with fever.
A healthy body works best at this specific temperature, which is why it is used as a baseline. The thermometer often has a red mark at 37°C so the doctor can instantly see if the reading is too high.
Teacher's Tip: 37 is the "Safe Zone" for humans.
Exam Tip: If you are asked to state "fever," explain that it is any temperature *above* the healthy average of 37°C.

Question 23: Can a clinical thermometer be used to measure the temperature of the boiling water ? Give reason for your answer.
Answer: No, a clinical thermometer cannot be used to measure the temperature of boiling water. The reasons are 1. It has a very small range. 2. It can break on cooling and on excess heating.
Boiling water is 100°C, but clinical thermometers only go up to 42°C. If you put one in boiling water, the mercury would expand so much that it would likely shatter the glass tube.
Teacher's Tip: Don't put a "Small Range" tool in a "High Heat" situation!
Exam Tip: Mention the specific range (35°C-42°C) and the boiling point (100°C) to prove your answer.

Question 24: Explain the term ‘area of a surface’.
Answer: The total surface occupied by an object is called its area or surface area.
Area tells us how much "covering" space an object takes up in two dimensions. We measure this to know things like how much paint is needed for a wall or how much grass will fit in a yard.
Teacher's Tip: Area is "Length × Width".
Exam Tip: Use the term "two-dimensional" to describe area accurately in scientific answers.

Question 25: Name the S.I. unit of area and define it.
Answer: The S.I. unit of area is square metre or meter2 which in short form is written as m². One square metre is the area of a square of each side one metre.
Just like a metre measures a straight line, a square metre measures a flat box shape that is 1 metre long and 1 metre wide. It is the international standard for measuring all surfaces.
Teacher's Tip: Imagine a big square tile that is exactly 1 metre on every side.
Exam Tip: Always write the unit as m² with the 2 as a superscript.

Question 26: How are the units 1. square yard 2. hectare 3. km² 4. cm² 5. mm² related to the S.I. unit of area ?
Answer:
(i) square yard : One square yard is the area of a square of each side 0.836 metre. 1 square yard = 1 yard × 1 yard = 0.9144 m × 0.9144 m = 0.836 m² (or 0.84 m² nearly)
(ii) hectare : One hectare is the area of a square of each side 100 metre. Thus, 1 hectare = 100 metre × 100 metre = 10000 metre² (or 10⁴ m²)
(iii) km² : One square kilometre is the area of a square of each side 1 kilometre. Thus, 1 km² = 1 km × 1 km = 1000 m × 1000 m = 10⁶ m²
(iv) cm²2 : 1 cm² = (1/100 m) × (1/100 m) = 1/10000 m²= 110^-4 m²
(v) mm² : 1 mm² = 10^-6} m²
By comparing these units to the square metre, we can understand exactly how much larger or smaller they are. This system of relationships allows us to convert between field measurements (hectares) and laboratory measurements (cm²) easily.
Teacher's Tip: Hectare is used for farms, km² is for countries!
Exam Tip: Memorize the factor of 10,000 for converting between hectares and square metres.

Question 27: Explain how you will measure the area of (i) a square (b) a leaf?
Answer: The area of a square can be calculated by using the following formula – 1. Area of square of side l = side × side = l × l = L². The area of a leaf is obtained by using a graph paper. A graph paper has small squares of each side 1 mm. The area of each big square is 1 cm². Procedure: Place the leaf on graph paper. Draw its outline on the paper and remove it. Now count the number of complete squares. To this add the number of incomplete squares which are half or more than half. Ignore the squares which are less than half. Thus, Approximate area = (No. of complete squares + no. of half or more than half of incomplete squares) × area of one square.
Regular shapes like squares can be measured with a simple ruler and math formula. Irregular shapes like leaves require a "square counting" method on grid paper to get a good estimate of the surface they cover.
Teacher's Tip: Counting squares is like building a puzzle of the object's surface.
Exam Tip: For the leaf experiment, clearly state that squares less than half are ignored to avoid overestimating.

ADDITIONAL QUESTIONS

CHECK YOUR PROGRESS 1

A. State if the following statements are true or false. Correct the statement if it is false.

1. In ancient times, a cubit was used to measure the mass of an object.
Answer: False. In ancient times, a cubit was used to measure the length of an object.
A cubit was the distance from the elbow to the tip of the middle finger. It was a very common unit of length before standardized rulers were invented.
Teacher's Tip: Think of your arm; that's your personal "cubit" ruler!
Exam Tip: Always provide the corrected statement for "False" answers to get full marks.

2. There are seven base units in the SI system.
Answer: True
These seven units (length, mass, time, temperature, current, intensity, and substance amount) are the foundation of all other scientific measurements. Every other unit in physics is built by combining these seven.
Teacher's Tip: They are like the seven "Primary Colors" of the measurement world.
Exam Tip: You only need to know the first four for this chapter (length, mass, time, temperature).

3. Second is considered as the fundamental unit of time in both CGS and MKS systems.
Answer: True
Even though mass and length units change between these systems, the "second" remains the same. It is the most universal unit across almost all scientific measurement frameworks.
Teacher's Tip: "Time" waits for no system - it's always seconds!
Exam Tip: Remember that CGS stands for Centimetre-Gram-Second and MKS stands for Metre-Kilogram-Second.

4. Centi mean ‘a hundredth part’.
Answer: True
The prefix "centi-" comes from the Latin word "centum," meaning hundred. It tells us that we have divided a unit into 100 equal pieces.
Teacher's Tip: Think of a "century" having 100 years or a "cent" being 1/100 of a dollar.
Exam Tip: Use this to remember that 100 cm = 1 metre.

5. The symbol used for a unit is always written in capital letters.
Answer: False. The symbol used for a unit is normally written in small letters.
Most symbols, like 'm' for metre or 's' for second, are lowercase. Capital letters are only used when a unit is named after a specific scientist, like 'K' for Kelvin.
Teacher's Tip: Lowercase is for the units; Uppercase is for the "Scientists".
Exam Tip: Be very careful with 'kg'—both letters must be lowercase!

B. Answer the following in short.

Question 1: What do you understand by the term ‘measurement’?
Answer: Determining the exact value of an unknown quantity by comparing it with a known fixed quantity is called as measurement.
Measurement helps us turn our observations into precise numbers that everyone can understand. It is the difference between saying something is "big" and saying it is "5 metres long."
Teacher's Tip: Measurement is just "Comparing stuff to a standard."
Exam Tip: Include the phrase "known fixed quantity" to define the unit correctly.

Question 2: What are derived physical quantities? Give any two examples of derived physical quantities.
Answer: Physical quantities that are derived from one or more fundamental physical quantities are called derived physical quantities. Examples: area, volume, speed, density, etc.
Derived quantities are "made" by doing math with the fundamental units. For example, area is length × length, so it is derived from the fundamental unit of length.
Teacher's Tip: Fundamental units are the "ingredients," and derived units are the "recipe".
Exam Tip: Area (m²) is the best example to use because it clearly shows two lengths combined.

Question 3: What are the characteristics of a standard unit?
Answer: 1. It should be accepted universally. 2. It should be accurate. 3. It should be neither too small nor too big and easy to use.
A standard unit acts as a reliable reference point that doesn't change over time or from person to person. Without these traits, a measurement taken in India might not mean the same thing in America.
Teacher's Tip: A standard unit must be "Global," "Correct," and "Convenient."
Exam Tip: Listing these three points as numbered items will ensure you get full marks for this question.

Question 4: Mention any two advantages of the metric system over traditional units.
Answer: 1. The metric units are accurate whereas the traditional units were not uniform. 2. The metric system is accepted globally whereas the traditional units had different values at different places.
The metric system fixed the problem of people using their own body parts (like feet or hands) to measure things. It replaced local guesswork with precise, international standards that stay the same everywhere.
Teacher's Tip: Metric is "The Same for Everyone," everywhere.
Exam Tip: Use the word "Uniformity" to describe how metric units stay the same.

Question 5: Which institution in the world maintain the guidelines for using the SI units correctly ?
Answer: General Conference of Weights and Measures.
This international organization meets regularly to ensure the definitions of our units remain perfectly accurate as technology improves. They are the "bosses" of the measurement world.
Teacher's Tip: It's like the "United Nations" of Rulers and Scales!
Exam Tip: Memorize the full name: General Conference of Weights and Measures.

C. Answer the following in detail.

Question 1: What are fundamental physical quantities? Name any three fundamental physical quantities.
Answer: Basic physical quantities that do not depend upon other quantities are called fundamental physical quantities. There are seven fundamental quantities – length, mass, temperature, time, electric current, luminous intensity and amount of substance.
Fundamental quantities are the simplest things we can measure. You don't need a math formula to find them; you just use a basic tool like a ruler for length or a clock for time.
Teacher's Tip: They are the "Originals"—everything else is built from them.
Exam Tip: If asked for three, always choose Length, Mass, and Time as they are the easiest to remember.

Question 2: Explain by giving two examples why the measurement of a physical quantity is expressed as a combination of a numeral and a unit.
Answer: To measure a physical quantity, we need to compare it with a known fixed physical quantity of the same kind, i.e., a unit. Hence, the measurement of a physical quantity is always written as a combination of a numeral along with the unit. The numeral specifies the number of times the unit is repeated. Example:
1. Using a centimetre scale, the length of pencil box is found to be 20 centimeters (cm). 20 cm simply means that the length is 20 times a centimetre. (The centimetre forms the unit of length in a centimetre scale.) Here, the number 20 is the numeral (magnitude) and cm is the unit.
2. Using a weighing (kilogram) scale, the weight of the box is found to be 2 kilograms (kg) 2 kg simply means that the mass of the box is 2 times a kilogram. (The kilogram forms the unit of mass in a kilogram scale). Here, the number 2 is the numeral (magnitude) and kg is the unit.
A number alone doesn't tell us "what" was measured, and a unit alone doesn't tell us "how much." By combining them, we create a complete picture that precisely describes the object's magnitude.
Teacher's Tip: Number = Magnitude; Unit = Standard. You need both to tell the whole story!
Exam Tip: Use the pencil box example (20 cm) as it is easy to draw and explain in a few lines.

Question 3: Explain in detail why there was a need to standardize units.
Answer: The traditional units were not uniform as the length of a cubit, foot and handspan varied from person to person according to their body size. Similarly, there was no certainty that all grains were exactly the same weight. So these units could not be used for scientific measurements where accuracy was a prime concern. The development of a large number of systems of measurement also made it very difficult to conduct trade and commerce between different socities. Therefore, people felt the need to have standard units which could be used for accurate measurement and were accepted universally.
Imagine buying cloth using a merchant's "foot" when their feet are smaller than yours! Standardization ensures fairness in trade and precision in science so that a "metre" is the same length for everyone on Earth.
Teacher's Tip: Different body sizes meant different measurements—it was a mess!
Exam Tip: Mention "Trade and Commerce" as a key reason why universal units were necessary.

Question 4: Why are multiples and submultiples of SI units required?
Answer: Sometimes, the size of the SI unit is either too small or too big to measure a certain quantity. For example, a metre is too small a unit to measure the distance between two cities and too big a unit to measure the thickness of a wire. Hence, multiples and submultiples of units are required. Multiples are factors used to create larger forms whereas submultiples are factors used to create smaller forms of the SI units. For example, a centimetre is a submultiple and kilometre is a multiple of a metre.
Using the right scale makes numbers easier to work with and understand. We wouldn't want to say the distance to the moon is millions of millimeters; using kilometers instead makes much more sense.
Teacher's Tip: It's like having a giant ruler for mountains and a tiny ruler for ants.
Exam Tip: Use the example of km vs mm to explain why we need multiple sizes of the same unit.

Question 5: State some common rules to write SI units correctly.
Answer: Guidelines for capitalization:
1. If a unit is derived from the name of a person, its name is always written in small letters. Example: newton (not Newton).
2. A unit not named after persons is written in small letters. Example: metre (not Metre).
3. The symbol used for a unit is normally written in small letters. Example: metre : m.
4. If the symbol of unit is derived from the name of a person, it is written in capital letters. Example: newton : N.
5. If a unit is represented by more than one letters, the first letter of the symbol is capitalized. Example: pascal : Pa.
Guidelines for Plurals:
The plural form is used only when the unit is written in full. Symbols of units are never written in plural. Example: 10 metres : 10 m (not 10 ms).
Guidelines for punctuation:
A full stop is never put at the end of a unit symbol unless it occurs at the end of a sentence. Example: “It is 50 cm long.” but not “It is 50 cm. long.”
Following these rules ensures that scientific data is uniform and professional. Little details like avoiding plural symbols (kgs) or misplaced periods prevent mistakes in technical drawings and research papers.
Teacher's Tip: Full names are lowercase, but symbols are Uppercase ONLY if it's a person's name!
Exam Tip: This is a high-mark question. Listing the capitalization and plural rules separately will show great organization.

Check Your progress

A. Tick the most appropriate answer.

1. The SI unit of mass is
1. gram 2. milligram 3. kilogram 4. pound
Answer: 3. kilogram
While all of these are used to measure mass, the Kilogram is the official standard for the International System (S.I.). One kilogram is approximately the mass of a liter of water.
Teacher's Tip: "Kilo" is the King of mass units!
Exam Tip: Don't pick "gram" just because it's common; always look for the "S.I." keyword.

2. To measure the volume of an irregular shaped body, we use a
1. graph paper 2. beam balance 3. measuring cylinder 4. ruler
Answer: 3. measuring cylinder
By dropping an irregular object into water, we can see how much the water level rises. This "displacement" tells us the exact volume of the object, which we couldn't find with a ruler.
Teacher's Tip: Think of Archimedes in the bathtub! Water displacement is the trick.
Exam Tip: Remember that graph paper is for area, but cylinders are for volume.

3. Which of the following weighing devices has a very high accuracy and sensitivity ?
1. Beam balance 2. Grocer’s balance 3. Physical balance 4. Spring balance.
Answer: 3. Physical balance
A physical balance is designed for scientific laboratories where even the weight of a piece of hair might matter. It has very fine parts that detect tiny differences in mass.
Teacher's Tip: "Physical" here means it's used in Physics labs for super-precise work.
Exam Tip: This is the best tool for measuring very light or expensive substances like gold or chemicals.

B. State if the following statements are true or false. Correct the statement if it is false.

1. Area of an object is a fundamental physical quantity.
Answer: False. Area of an object is a derived physical quantity.
Area is not measured by itself; it is calculated by multiplying two lengths together. Because it depends on another unit (length), it is considered "derived."
Teacher's Tip: If you need a math formula (like L × W), it's derived!
Exam Tip: Memorize the seven fundamental quantities so you can easily spot the derived ones.

2. The error in reading a scale due to the wrong positioning of the eye is called human error.
Answer: False. The error in reading a scale due to the wrong positioning of the eye is called parallax error.
Human error is too general; the specific scientific name for looking at a scale from an angle is parallax. To fix it, you must always look perfectly perpendicular to the scale.
Teacher's Tip: Look straight at it, or it will be a "Parallax" mistake!
Exam Tip: Use the term "parallax error" specifically whenever eye positioning is mentioned.

3. The region enclosed within the boundaries of a two-dimensional figure is called its area.
Answer: True.
Area measures how much surface a flat shape takes up. This is different from volume, which measures three-dimensional space inside a container.
Teacher's Tip: Area is the "Face" of a shape.
Exam Tip: If a question says "enclosed boundaries" in 2D, the answer is always area.

4. The length of an irregular object can be found with the help of a graph paper.
Answer: False. The area of an irregular object can be found with the help of a graph paper.
A graph paper allows you to count squares to estimate the surface space of things like leaves or handprints. Length of an irregular line is better measured with a string and a ruler.
Teacher's Tip: Graphs are for counting "Squares" (Area), not lines.
Exam Tip: If the question is about "irregular objects," differentiate between using a string (for length) and graph paper (for area).

C. Match the following.

Column A
1. Length
2. Mass
3. Area
4. Volume

Column B
a. kilogram
b. cubic metre
c. metre
d. square metre
Answer:
1. Length - c. metre
2. Mass - a. kilogram
3. Area - d. square metre
4. Volume - b. cubic metre
1-c, 2-a, 3-d, 4-b
Matching these quantities to their units is the first step in scientific literacy. Notice how area and volume are built directly from the base unit for length (metre).
Teacher's Tip: One dimension = m; Two = m²; Three = m³.
Exam Tip: For volume, remember the term "cubic" always goes with the number 3 or m³.

D. Answer the following in short.

Question 1: Which unit will you use to find the length of your notebook and why ?
Answer: Centimetre. Because a notebook has a length for which metre would be too large a unit to measure and millimetre would be too small.
Choosing the right unit makes your measurement easy to read and understand. For small objects like books or pencils, the centimetre is the most "convenient size."
Teacher's Tip: Always pick the "Goldilocks" unit—not too big, not too small!
Exam Tip: Mention the word "convenient" to show you understand the purpose of choosing specific units.

Question 2: What do you understand by the term ‘mass’ ? Name any one instrument used for weighing.
Answer: The amount of matter present in an object is called its mass. Instruments used to measure mass are beam balance, spring balance, physical balance, electronic weighing machines, etc.
Mass doesn't change based on where you are; it's just the total count of the particles in your body. We use scales and balances to compare an object's pull of gravity or its inertia to find its mass.
Teacher's Tip: Mass = Total amount of "Stuff."
Exam Tip: "Electronic weighing machine" is a great modern example to give alongside the traditional beam balance.

Question 3: Explain the working of a beam balance.
Answer: A beam balance is the simplest instrument to measure mass (weight). In a beam balance, the mass of an object is measured by comparing it with standard masses called standard weights. A simple beam balance consists of a straight beam of a metal (generally iron), supported at its centre with the help of an iron loop. A pointer is fixed at the centre of the iron loop. Two identical pans are suspended at equal distances from the centre, at the two ends of the beam. Working : The object whose mass has to be measured is placed on one of the pans (generally the right pan). Standard weights are placed on the other pan until the metallic beam becomes horizontal and the pointer becomes vertical. The sum total of all weights used gives the mass of the object.
This tool works on the principle of moments, where a balance is achieved when both sides are equal. By using fixed weights that everyone agrees upon, we can accurately calculate the mass of any mystery object.
Teacher's Tip: It's all about making that center pointer stay perfectly straight!
Exam Tip: Clearly explain the role of the "pans" and the "standard weights" for a complete description.

E. Find the area of these leaves, where 1 square on the graph paper represents 1 cm².
Answer:
1. Area of leaf 1 = 1 × (Number of complete squares) cm² + 1/2 × (Number of half or more than half squares) cm² = 1 × 3 cm² + 1/2 × 5 cm² = 3 cm² + 2.5 cm² = 5.5 cm²
2. Area of leaf 2 = 1 × 3 cm² + 1/2 × 5 cm² = 3 cm² + 2.5 cm² = 5.5 cm²
3. Area of leaf 3 = 1 × 7 cm² + 1/2 × 9 cm² = 7 cm² + 4.5 cm² = 11.5 cm²
4. Area of leaf 4 = 1 × 6 cm² + 1/2 × 8 cm² = 6 cm² + 4 cm² = 10 cm²
5. Area of leaf 5 = 1 × 6 cm² + 1/2 × 9 cm² = 6 cm² + 4.5 cm² = 10.5 cm²
This method turns an irregular object into a set of "countable" squares. By combining full and partial squares, we get a very close estimate of the leaf's total surface area.
Teacher's Tip: It's like counting tiles on a floor that a rug is covering.
Exam Tip: Always show your addition (6 + 4.5) clearly to avoid points lost for calculation errors.

Exercises

A. Tick the most appropriate answer.

1. Which of the foliowing is a fundamental physical quantity?
1. Speed
2. Area
3. Volume
4. Time
Answer: Time
Time is a base quantity that doesn't need other measurements to define it. Speed, Area, and Volume are all derived because they require mathematical formulas involving length and time.
Teacher's Tip: Fundamental quantities are the "building blocks" of physics.
Exam Tip: Memorize the "Big Four" fundamentals for this grade: Length, Mass, Time, and Temperature.

2. The system of measurement based on centimetre-gram- second is known as
1. SI system
2. FPS system
3. MKS system
4. CGS system
Answer: CGS system
The name "CGS" is literally made from the first letters of its base units: Centimetre, Gram, and Second. It was a very common system before the SI system was fully adopted.
Teacher's Tip: Just look at the first letters: C-G-S.
Exam Tip: Be careful not to confuse it with MKS (Metre-Kilogram-Second).

3. The region enclosed within the boundaries of a closed figure is known as its
1. length
2. area
3. volume
4. temperature
Answer: area
This is the standard definition of a flat surface's size. Length only covers one direction, and volume covers three; area is the "sweet spot" for 2D shapes.
Teacher's Tip: Area is "How much paint would cover this?"
Exam Tip: Whenever you see "region enclosed," think of the surface area.

4. Which of the following devices is used to measure mass?
1. Ruler
2. Measuring cylinder
3. Beam balance
4. Stopwatch
Answer: Beam balance
A beam balance compares the gravitational pull on an unknown object against known weights. Rulers measure length, cylinders measure volume, and stopwatches measure time.
Teacher's Tip: Use a balance to find the "Balance" between two masses!
Exam Tip: Make sure you can name at least one tool for every fundamental quantity.

5. Which of the following is not a common unit for measuring time ?
1. Hour
2. Mean solar day
3. Year
4. Sundial
Answer: Sundial
A sundial is an instrument used to tell time, not a unit of measurement. Units are the names of the "standard parts" of time, like hours or years.
Teacher's Tip: Units are the "last names" of numbers; tools are the objects you hold.
Exam Tip: Don't confuse the *tool* (thermometer, sundial) with the *unit* (°C, hour).

6. A train departs from Delhi railway station at 21:50 hours every day. The time shown in you analogue watch at the departure will be
1. 2:50 a.m
2. 9:50 p.m.
3. 9:50 a.m.
4. 11:50 p.m.
Answer: 9:50 p.m.
In the 24-hour clock, any number above 12 is in the afternoon (P.M.). To find the regular time, you subtract 12 from the hours: 21 - 12 = 9.
Teacher's Tip: If the hour is > 12, subtract 12 and add "P.M."!
Exam Tip: Practice converting between 12-hour and 24-hour formats to avoid errors in time problems.

7. The total number of divisions in the Celsius scale is
1. 90
2. 100
3. 180
4. 360
Answer: 100
The scale is designed to go from 0°C (freezing) to 100°C (boiling), which means there are exactly 100 equal steps in between. This makes it a very easy decimal-based system to use.
Teacher's Tip: "Centigrade" literally means "hundred steps."
Exam Tip: If you forget, just subtract the freezing point from the boiling point (100 - 0 = 100).

8. The maximum and minium thermometer is commonly used by a
1. doctor
2. student
3. meteorologist
4. goldsmith
Answer: meteorologist
Meteorologists need to know the highest and lowest temperatures of the whole day to track weather patterns. This special thermometer records both extremes automatically so they don't have to watch it all day.
Teacher's Tip: "Meteorologist" is just a fancy word for a weather scientist.
Exam Tip: Match the thermometer type to the job: Clinical for Doctors, Max/Min for Weather.

B. Fill in the blanks.

1. There are seven fundamental physical quantities.
Answer: seven.
These seven quantities form the "DNA" of every other measurement in science. While we only focus on a few now, they include electricity, light, and chemical amounts too.
Teacher's Tip: Think of them as the 7 "Rainbow Colors" of measurement.
Exam Tip: If you list them, always include Length, Mass, and Time as the most important ones.

2. In the CGS system, length is measured in centimeters.
Answer: centimeters.
The 'C' in CGS stands for Centimeter, which is a smaller unit used for measuring things like the length of a desk or a book. It is exactly 1/100 of a metre.
Teacher's Tip: "C" is for Centimeters!
Exam Tip: Be careful with spelling; both "centimetre" and "centimeter" are acceptable, but stay consistent.

3. 1 kilometre is equal to 1000 metres.
Answer: 1000.
"Kilo" is a prefix that always means 1000. So, whether it's kilometers or kilograms, it always represents a thousand of the base unit.
Teacher's Tip: Kilo = 1000. Memorize this "secret code" prefix!
Exam Tip: Use this conversion whenever you are calculating distances between cities.

4. The amount of matter contained in a body is known as its mass.
Answer: mass.
Mass measures the physical substance inside an object and stays the same even if you go to the moon. It is different from weight, which depends on gravity.
Teacher's Tip: Mass is the amount of "Stuff" inside you.
Exam Tip: This is a textbook definition; writing it verbatim will guarantee full marks.

5. The first two digits in a 24 hour time fomiat represent the number of hours.
Answer: hours.
In the format "HH:MM", the first part shows the elapsed hours since midnight. For example, in 14:30, the "14" tells us it is 2 o'clock in the afternoon.
Teacher's Tip: 24-hour time is like a "Lap Counter" for a whole day.
Exam Tip: Remember that the digits *after* the colon always represent the minutes.

6. If the departure time of a train on a railway ticket is printed as 20:35, then it will depart at 8.35 p.m.
Answer: 8.35 p.m.
By subtracting 12 from 20, we get 8. Since it was more than 12, we know it is in the post-meridian (P.M.) part of the day.
Teacher's Tip: Take away 12 and add the P.M. tag!
Exam Tip: Always include the "p.m." or "a.m." when converting back to the 12-hour clock.

7. The lower fixed point in a laboratory thermometer is the same as that of -10°C.
Answer: -10°C. (Note: While some are 0°C, the text specifies a broader range for lab thermometers).
Laboratory thermometers need to measure colder things than just freezing water, so they often start as low as -10°C. This allows scientists to track temperatures of cooling mixtures.
Teacher's Tip: Lab thermometers are for "Hard Work" and have bigger ranges.
Exam Tip: Contrast this with the clinical thermometer, which starts at 35°C.

8. The temperature at which water freezes is known as ice point.
Answer: ice point.
The "ice point" is a fixed reference used to calibrate instruments. For pure water at sea level, this is exactly 0°C.
Teacher's Tip: Ice Point = Freezing Point.
Exam Tip: Be ready to define the "Steam Point" as the boiling point of water (100°C).

C. State if the following statements are true or false. Correct the statement if it is false.

1. The average of a group of observations is calculated by adding all the observations and dividing the sum by the number of observations.
Answer: True
Finding an average helps cancel out small mistakes in individual readings to give a more reliable result. It is a common mathematical tool used in almost all scientific experiments.
Teacher's Tip: Average = Sum / Count.
Exam Tip: Always show your addition and division steps when asked to calculate an average.

2. A laboratory thermometer has a kink in its capillary tube.
Answer: False. A clinical thermometer has a kink in its capillary tube.
Laboratory thermometers must respond instantly to temperature changes, so they don't have a kink. Only clinical ones have it so the mercury stays put for a doctor to read.
Teacher's Tip: The "Kink" is only for "Clinic" use!
Exam Tip: This is a classic trick question—remember that lab thermometers are straight tubes.

3. Water is the most commonly used thermometric substance.
Answer: False. Mercury is the most commonly used thermometric substance.
Water is a poor choice because it freezes at 0°C and doesn't expand uniformly. Mercury expands predictably and doesn't stick to glass, making it ideal for thermometers.
Teacher's Tip: Water would "Freeze" in a winter thermometer—that's why we use Mercury!
Exam Tip: Identify "Mercury" as the correct thermometric substance for full marks.

4. Mercury does not stick to the surface of glass.
Answer: True
Because mercury doesn't stick, it can move up and down the thin tube smoothly and leave no droplets behind. This ensures the reading is perfectly clear and accurate every time.
Teacher's Tip: Mercury is "Slippery"—it won't leave a mess on the glass.
Exam Tip: This non-stick property is one of the main reasons mercury is used in precision thermometers.

5. 1 m = 10,000 cm²
Answer: False. 1 m² = 10,000 cm².
The original statement tried to equate a length (1 m) with an area (10,000 cm²), which is scientifically impossible. When squaring the length to find area, 100 cm × 100 cm equals 10,000 cm².
Teacher's Tip: You can't compare "Lines" to "Squares"!
Exam Tip: Always check the units (m vs m²) before agreeing with a math statement.

6. A ruler with a damaged end can be used to measure a length accurately.
Answer: True
Even without the zero mark, you can start your measurement at a clear point like 1 cm or 2 cm. You then just subtract that starting number from your final reading to get the real length.
Teacher's Tip: Just start at "1" and subtract 1 from your answer!
Exam Tip: Describe the "subtraction method" if you are asked to explain why this is true.

D. Answer the following in a word or two or in a sentence.

Question 1: Name the unit which is commonly in both the MKS and CGS systems.
Answer: Second (unit of time)
Time is the most consistent dimension in all metric-style measurement systems. While mass and length units are adjusted for scale, the second remains the universal base for time.
Teacher's Tip: Second stays second—it never changes systems!
Exam Tip: This is a very common one-word answer question; learn it well.

Question 2: Name an instrument generally used to find the time interval between two events accurately.
Answer: Stop watch.
A stop watch is designed specifically to be started and stopped by the user to measure duration. It is much more accurate for timing races or reactions than a standard clock.
Teacher's Tip: It "Stops" on command so you can see the interval.
Exam Tip: Do not just say "clock"; use the word "stopwatch" for accuracy-based questions.

Question 3: If the alarm of a digital clock is set at 05:50, at wdiat time will the alarm ring during the day ?
Answer: 5.50 a.m.
In the 24-hour format, "05:50" represents the early morning because it is before 12:00. This is the time when most people would be waking up for school or work.
Teacher's Tip: 05 means 5 o'clock in the morning.
Exam Tip: Always include "a.m." for times before noon and "p.m." for times after.

Question 4: At what temperature is the upper fixed point of a clinical thermometer kept?
Answer: 42°C Cor 108°F.
Clinical thermometers have a very limited range because the human body can only survive within a narrow set of temperatures. If a person reached 42°C, they would be extremely ill, so there is no need for higher markings.
Teacher's Tip: Clinical thermometers are "Specialists" for body heat only.
Exam Tip: Memorize both 42°C and 108°F as the upper limits.

Question 5: Write the formula for finding the average of a given set of observation.
Answer: Average = sum of all observations / number of observations
This formula allows us to find the central value for a group of measurements. It is the best way to handle scientific data when you have taken the same measurement multiple times.
Teacher's Tip: Average is the "Middle Ground" of your data.
Exam Tip: Write the formula clearly in words like "Sum" and "Number" for full marks.

E. Answer the following in short.

Question 1: What is parallax error ?
Answer: The error that can arise due to the wrong positioning of the eye while reading a scale is called parallax error.
If you look at a mark from the left or right, it will appear to line up with a different number on the scale. This is a common mistake that can easily be fixed by looking directly from above.
Teacher's Tip: Use your finger to point straight down at the line to stay accurate!
Exam Tip: Mention "perpendicular view" as the solution to prevent parallax error.

Question 2: Explain the working of an extension spring balance.
Answer: When a body to be weighed is attached to the hook, the coil is stretched downwards. The distance through which the spring gets stretched is measured by a pointer and a graduated scale attached to the spring. The reading on the scale gives the weight of the object.
This device works on the principle that the more force (weight) you apply, the more a spring will stretch. By measuring that stretch on a pre-marked scale, we can quickly determine the mass of any hanging object.
Teacher's Tip: The harder you pull, the longer the spring gets!
Exam Tip: Use the terms "hook," "stretch," and "graduated scale" in your explanation.

Question 3: What do you mean by a mean solar day ?
Answer: Mean solar day is the time taken by the earth to make one complete rotation about its own axis.
This rotation is what gives us the cycle of day and night. We divide this full rotation into 24 hours to help organize our daily schedules.
Teacher's Tip: A solar day is just one full "Spin" of the Earth.
Exam Tip: If asked about seconds, remember that one mean solar day is exactly 86,400 seconds.

Question 4: Why is there a slight bend in the capillary tube of a clinical thermometer near the bulb ?
Answer: A slight bend or kink in the capillary tube of the clinical thermometer near the bulb ensures that the mercury does not move back into the bulb when the thermometer is taken out of a person’s mouth for reading.
This kink acts as a "freeze-frame" for the temperature. It allows the doctor to take the thermometer to a light and read it carefully without the mercury dropping as it cools in the air.
Teacher's Tip: The bend is like a "One-Way Road" for mercury.
Exam Tip: Use the words "constriction" or "kink" to describe this special bend.

Question 5: What is the function of the bulb in a thermometer ?
Answer: The bulb in a thermometer is filled with mercury. When the bulb is heated, mercury in the bulb expands and rises up in the capillary tube. The height of the mercury gives the reading of temperature.
The bulb is the "sensor" that touches the hot or cold object. Its job is to hold the liquid that will expand and move up the tube to show us the temperature.
Teacher's Tip: The bulb is where all the "Mercury Action" starts!
Exam Tip: Mention "expansion on heating" to explain why the mercury moves out of the bulb.

Question 6: Describe any two means by which the actual capacity’ of a measuring container can be made less than the correct value by a dishonest trader.
Answer: 1. The base of the measuring container can be bend inwards by hammering which reduces the capacity of liquid it can hold. 2. Some lead can be poured into the measuring container.
These tricks change the "inside room" of a container without changing its outside appearance. This means the buyer thinks they are getting a full liter, but the container actually holds less.
Teacher's Tip: Dishonest people try to "Steal Space" from the container.
Exam Tip: Understanding these tricks helps you realize why standardizing and checking units is so important for fair trade.

F. Answer the following in detail.

Question 1: What do you understand by the terms volume and capacity ? which is the most suitable unit for measuring the volume of a/an (a) glass filled with water (b) swimming pool (c) air inside an inflated balloon (d) cylinder of a car engine
Answer: The total space occupied by an object is called its volume. The maximum volume of a liquid that a container can hold is known as its capacity. Capacity and volume have same units – litres (L) and millilitres (mL). (a) millilitre(mL) (b) cubic metre (m³) . (c) millilitre (mL) (d) cubic centimetre (cc) or cm³.
Volume is how much space an object *takes up*, while capacity is how much a container *can hold*. Even though they measure the same 3D space, we use these different terms to distinguish between objects and containers.
Teacher's Tip: Volume = Space Taken; Capacity = Space Available.
Exam Tip: Use "cubic metre" for very large volumes like pools and "mL" for small daily items like glasses.

Question 2: Explain in detail why railways and airlines use the 24-hour clock format.
Answer: Railways and airlines use the 24-hour clock format as they operate round the clock (24 hour). The main features of 24-hour clock system are: 1. a.m. and p.m. are not used in order to avoid confusion. 2. Time is shown by 4 digits. The first two digits indicate the number of hours, and the next two digits indicate the number of minutes. 3. Time is expressed continuously from 00.00 (midnight) to 24:00.
In a global transport system, mixing up 8:00 A.M. and 8:00 P.M. could cause huge disasters. Using a continuous 24-hour scale ensures there is only one way to interpret a departure time, making travel much safer and more organized.
Teacher's Tip: It's the "No Confusion" clock!
Exam Tip: Mention that it operates "round the clock" as a primary reason for its use in travel.

Question 3: What do you understand by the term temperature? Distinguish betw een laboratory and clinical thermometers.
Answer: The degree of hotness or coldness of an object is called its temperature.
Laboratory thermometer: (i) It is used to measure temperatures for scientific purposes in a laboratory. (ii) The kink is not present. (iii) The lower fixed point is -10°C and upper fixed point is 110°C.
Clinical thermometer: (i) It is used to measure temperature of the human body. (ii) A slight bend or kink is present near the bulb. (iii) The lower fixed point is 35°C or 95°F and the upper fixed point is 42°C or 108°F.
Lab thermometers are for general science and need a wide range to measure boiling or freezing chemicals. Clinical ones are specialized "medical" tools that only care about the narrow range of human health.
Teacher's Tip: Lab = Large range; Clinic = Close range (plus a kink!).
Exam Tip: Creating a table is the best way to present this comparison for maximum marks.

Question 4: When are approximations necessary in daily life and when should they be avoided ?
Answer: An approximation or estimation is a reasonable guess about the measure of a physical quantity. For example, we use approximation in adding salt to food while cooking. We use approximation when we try to figure out the time it would take to reach a certain place by car. In our daily life, we use approximations in many situations. They are useful as they save time. But, since they are not accurate in measurements, they should be avoided in scientific studies and experimentation.
Approximation is great when a small mistake won't hurt anything, like guessing how much milk to put in tea. However, in science or construction, being "close enough" isn't enough; you need exact numbers to make sure things work correctly or stay safe.
Teacher's Tip: Approximation is a "Shortcut," but science requires the "Whole Path."
Exam Tip: Use "cooking" and "scientific experiments" as your two main examples of when to use and when to avoid estimation.

G. Give reasons for the following.

Question 1: Body parts should not be used for correct measurements of an object.
Answer: Body parts have different sizes from person to person and hence the value varies. Since, there is no uniformity or accuracy in the reading, body parts should not be used for correct measurement of an object.
If you use your "foot" to measure a room, and your tall father uses his "foot," you will get two different answers. This lack of consistency makes it impossible to build things or trade fairly without standard tools like rulers.
Teacher's Tip: Everybody is different, so body rulers are always "Wrong"!
Exam Tip: Use the word "Uniformity" to explain why standardized tools are better than body parts.

Question 2: Measurements are very important for life.
Answer: We need to measure the quantities of most of the things around us to be able to take correct decisions regarding their utility. To find the exactness of an unknown quantity, we need its measurement.
Measurements allow us to bake perfect cakes, build strong houses, and take the right amount of medicine. Without them, our world would be full of dangerous guesswork.
Teacher's Tip: Measurement is the "Secret Language" that keeps the world running smoothly.
Exam Tip: Mention "exactness" as the goal of any measurement.

Question 3: Measuring units are standardized.
Answer: Measuring units are standardized so that accurate measurement can be done and are accepted universally.
Standardization means everyone on the planet agrees on what a "metre" or "kilogram" is. This agreement is the only way we can share scientific discoveries and do business across different countries without fighting over the "size" of things.
Teacher's Tip: Standardized means "Agreed upon by everyone."
Exam Tip: Connect "Standardization" to "Universal Acceptance" for a high-scoring answer.

H. Solve the following numerical problems.

Question 1: Express : (a) 2.25 m in cm (b) 6 L in mL (c) 8000 g in kg
Answer:
a. 2.25 m = 2.25 × 100 cm = 225 cm [As 1 m = 100 cm]
b. 6 L = 6 × 1000 mL = 6000 mL [As 1 L = 1000 mL]
c. 8000 g = 8000 / 1000 kg = 8 kg [As 1000 g = 1 kg]
To solve these, you just need to know the basic conversion factors (100 or 1000) and decide whether to multiply or divide. Going from a larger unit to a smaller one (like m to cm) always requires multiplication.
Teacher's Tip: "Litre to Milli" is just adding three zeros!
Exam Tip: Always write the bracketed reason (e.g., [As 1 m = 100 cm]) to show you know the rule.

Question 2: 20 one - rupee coins are placed one above the other. If their total height is 32 mm, find the thickness of one coin.
Answer: Number of coins 20; Total height of coins = 32 mm. Thickness of one coin = Height of all coins / Number of coins = 32 / 20 = 1.6 mm.
By measuring many objects together and then dividing, we can find the size of a single tiny object very accurately. This is a common scientific trick for items that are too small to measure clearly with a ruler on their own.
Teacher's Tip: This is the "Stack and Divide" trick for tiny things.
Exam Tip: Make sure your division is correct; 32 divided by 20 is 1.6.

Question 3: A piece of wire is wound around a pencil 60 times. If the total width of all the turns is 4 cm, find the diameter of the wire.
Answer: Number of turns of wire = 60; Total width of turns of wire 4 cm. Diameter of the wire = Total width of turns of wire / Number of turns of wire = 4 / 60 = 0.066 cm.
This is another example of using a group measurement to find a tiny individual size. Winding the wire tightly ensures that there are no gaps, so the total width is truly just the sum of the wire's diameters.
Teacher's Tip: Winding it up makes it "Thick" enough to measure easily.
Exam Tip: Round your final decimal to at least two or three places (0.066) for better precision.

Question 4: Amit dipped a stone tied with a string in a measuring cylinder filled with water. If the initial level of water was 56 mL and after dipping the stone the final level of water was 78 mL, find the volume of the stone.
Answer: Initial level of water = 56 mL; Final level of water = 78 mL. Volume of the stone = Final reading - Initial reading = 78 mL - 56 mL = 22 mL.
This is the displacement method, which works because two things cannot occupy the same space at the same time. The stone "pushes" the water up by exactly its own volume, which we can then read on the cylinder's scale.
Teacher's Tip: The "Rise" in water IS the volume of the stone.
Exam Tip: Always write the unit "mL" or "cm³" (remember 1 mL = 1 cm³) after your final number.

Question 5: Grass is to be laid a rectangular field of dimensions 55 m × 45 m. Calculate the area of the field.
Answer: Length of field = 55 m; Breadth of field = 45 m. Area of rectangular field = length × breadth = 55 × 45 m² = 2,475 m².
To find the area of any rectangle, you simply multiply the two side lengths together. This gives you the total number of "square metres" that make up the field's surface.
Teacher's Tip: Think of it as 45 rows with 55 square tiles in each row!
Exam Tip: Double-check your multiplication and don't forget the "²" in your area unit (m²).

Question 6: A lawn is in the shape of a square. Find the area covered by the lawn if each of its sides is 50 m.
Answer: Length of each side = 50 m. Area of square lawn = side × side = 50 × 50 m²= 2500 m².
A square is just a rectangle where all sides are equal, so the formula is simply the side length squared. 50 × 50 gives us a surface area of exactly 2500 square metres.
Teacher's Tip: Squaring a number ending in zero is easy: 5 × 5 is 25, then add two zeros!
Exam Tip: For squares, you only need one side measurement to find the area.

Question 7: An aeroplane leaves Bengaluru at 23:50 hours and reaches Chennal at 00.40 hours. Rewrite the statement using a 12- hour time format. Also find the duration of the flight.
Answer: Aeroplane leaves Bengaluru at 11:50 p.m. and reaches Chennai at 12:40 a.m. Duration of the flight = 50 minutes.
23:50 is just ten minutes before midnight (11:50 P.M.), and 00:40 is 40 minutes after midnight (12:40 A.M.). By adding the 10 minutes before and 40 minutes after midnight, we find the total flight time is 50 minutes.
Teacher's Tip: Crossing "Midnight" is like starting the clock over at zero.
Exam Tip: Break the time into two parts (before and after midnight) to make the subtraction easier.

Question 8: The body temperature of a patient on Monday was 102 °F and on Tuesday it was 104°F. What was the rise in temperature during these two days?
Answer: Body temperature on Monday = 102°F; Body temperature on Tuesday = 104°F. Rise in temperature = 104 - 102°F = 2°F.
To find a "rise" or "difference," you always take the higher value and subtract the lower one. In this case, the patient's fever increased by two degrees Fahrenheit between the two days.
Teacher's Tip: "Rise" just means the difference between the two numbers.
Exam Tip: Always include the degree symbol and the scale (°F) in your final subtraction result.

Question 9: The masses of five marbles are 50 g, 55 g, 60 g, 65 g and 70 g. Find their average mass.
Answer: The sum of masses of all marbles = 50 g + 55 g + 60 g + 65 g + 70 g = 300 g. Number of marbles = 5. Average mass of a marble = sum of mass / no. of marbles = 300 / 5 g = 60 g.
Average mass gives us a single number that represents the whole group. Notice that 60 g is right in the middle of our five values, which is exactly what an average should be.
Teacher's Tip: The average should always be somewhere between your smallest and biggest numbers.
Exam Tip: Check your addition twice; if the "Sum" is wrong, the "Average" will be too.

Question 10: The rainfall in a city on each day of a week is recorded below. Find the average rainfall for the week.
Answer: The sum of recorded rain fall = 1.2 mm + 10.3 mm + 5.5 mm + 13.5 mm + 7 mm + 1 mm = 38.5 mm. Number of days = 7. Average rainfall of the week = sum of all observations / number of days = 38.5 / 7 mm = 5.5 mm.
This calculation helps meteorologists describe a rainy week with one simple number. It shows that on average, 5.5 mm of rain fell each day, even though some days were much wetter than others.
Teacher's Tip: Dividing 38.5 by 7 is easy if you remember your 7-times tables (7 × 5 = 35).
Exam Tip: Make sure you use the total "7 days" for a week when calculating the average.