Samacheer Kalvi Class 9 Science Solutions Chapter 1 Measurement

I. Choose the correct answer :

 

Question 1. Choose the correct one.
(a) mm < cm < m < km
(b) mm > cm > m > km
(c) km < m < cm < mm
(d) mm > m > cm > km
Answer: (a) mm < cm < m < km
In simple words: This option correctly shows the order of length units from smallest to largest. Millimeters are the smallest, followed by centimeters, then meters, and finally kilometers are the largest unit among them.

🎯 Exam Tip: Remember the prefixes: milli (thousandth), centi (hundredth), kilo (thousand). This helps in quickly comparing units.

 

Question 2. Rulers, measuring tapes and metre scales are used to measure
(a) mass
(b) weight
(c) time
(d) length
Answer: (d) length
In simple words: Tools like rulers and measuring tapes are designed to find out how long something is. They help us measure the straight distance from one point to another, which is called length.

🎯 Exam Tip: Identify the basic function of each measuring tool. Rulers visually compare an object's dimension to a marked scale.

 

Question 3. 1 metric ton is equal to
(a) 100 quintals
(b) 10 quintals
(c) 1/10 quintals
(d) 1/100 quintals
Answer: (b) 10 quintals
In simple words: A metric ton is a very large unit of mass, commonly used for heavy items. It is the same as ten quintals. A quintal itself is 100 kilograms, so one metric ton is 1000 kilograms.

🎯 Exam Tip: Memorize common conversion factors between different units of mass like kilograms, quintals, and metric tons to avoid errors in calculations.

 

Question 4. Which among the following is not a device to measure mass?
(a) Spring balance
(b) Beam balance
(c) Physical balance
(d) Digital balance
Answer: (a) Spring balance
In simple words: A spring balance measures the *weight* of an object, which is a force. It works by how much a spring stretches. Other devices like beam, physical, and digital balances directly measure an object's *mass*.

🎯 Exam Tip: Understand the difference between mass (amount of matter) and weight (force due to gravity). Different instruments measure different quantities.

II. Fill in the blanks :

 

Question 1. Metre is the unit of ............
Answer: length
In simple words: The meter is the main way we measure how long things are in the SI system. It helps us understand size and distance easily.

🎯 Exam Tip: Always recall the standard SI unit for each fundamental quantity. For length, it is the metre.

 

Question 2. 1 kg of rice is weighed by ............
Answer: beam balance
In simple words: To accurately find the mass of things like rice, we use a beam balance. It works by comparing the rice to known standard masses.

🎯 Exam Tip: When choosing a measuring device, consider the quantity (mass, length, time) and the level of precision needed.

 

Question 3. Thickness of a cricket ball is measured by ............
Answer: vernier caliper
In simple words: A vernier caliper is a special tool used to measure small thicknesses, like that of a cricket ball, much more precisely than a regular ruler. This instrument helps in getting very accurate small measurements.

🎯 Exam Tip: For small, precise measurements like thickness or diameter, instruments like vernier calipers or screw gauges are more suitable than a meter scale.

 

Question 4. Radius of a thin wire is measured by ............
Answer: screw gauge
In simple words: A screw gauge is a very accurate tool used for measuring extremely small lengths, such as the radius of a thin wire. It can measure tiny dimensions with great precision.

🎯 Exam Tip: The screw gauge provides even higher precision than a vernier caliper, making it ideal for very thin objects like wires or sheets.

 

Question 5. A physical balance measures small differences in mass up to ............
Answer: 1mg or less
In simple words: A physical balance is a sensitive tool designed to detect very tiny changes in mass, down to one milligram or even smaller amounts. It is often used in laboratories where exact measurements are needed.

🎯 Exam Tip: Understand the precision of different balances: beam balances for general use, and physical/digital balances for very precise measurements (milligrams).

III. State whether true or false. If false, correct the statement :

 

Question 1. The SI unit of electric current is kilogram.
Answer: False. Correct statement: The SI unit of electric current is ampere.
In simple words: The kilogram is actually the SI unit for mass, not electric current. The correct SI unit for electric current is the ampere, named after a scientist.

🎯 Exam Tip: Clearly distinguish between the SI units for fundamental quantities like mass (kilogram), electric current (ampere), and temperature (kelvin).

 

Question 2. Kilometre is one of the SI units of measurement.
Answer: True.
In simple words: The kilometer is a unit of length that is part of the SI system, commonly used for measuring long distances. It is a multiple of the base unit, the meter.

🎯 Exam Tip: While metre is the base SI unit for length, its multiples (like kilometer) and sub-multiples (like millimeter) are also considered part of the SI system.

 

Question 3. In everyday life, we use the term weight instead of mass.
Answer: True.
In simple words: People often say "weight" when they actually mean "mass" in daily conversations. For example, we say we weigh 50 kg, but that is actually our mass.

🎯 Exam Tip: Be aware of the common usage versus the scientific definition; in physics, mass is constant, while weight can change with gravity.

 

Question 4. A physical balance is more sensitive than a beam balance.
Answer: True.
In simple words: Physical balances are built to be very precise and can measure tiny differences in mass much better than simple beam balances. This makes them suitable for laboratory use where high accuracy is needed.

🎯 Exam Tip: Higher sensitivity means an instrument can detect smaller changes in the measured quantity, leading to more accurate results.

 

Question 5. One Celsius degree is an interval of 1K and zero degree Celsius is 273.15 K.
Answer: True.
In simple words: When the temperature changes by one degree Celsius, it also changes by one Kelvin. Also, the temperature of zero degrees Celsius is equivalent to 273.15 Kelvin. This conversion helps us relate the two temperature scales.

🎯 Exam Tip: Remember the fixed conversion: \( 0^\circ \text{C} = 273.15 \text{ K} \). The size of a Celsius degree and a Kelvin are the same.

 

Question 6. With the help of vernier caliper we can have an accuracy of 0.1 mm and with screw gauge we can have an accuracy of 0.01 mm.
Answer: True.
In simple words: A vernier caliper can measure things accurately down to 0.1 millimeters, while a screw gauge is even more precise, measuring accurately down to 0.01 millimeters. This shows how precise these tools are for small measurements.

🎯 Exam Tip: Note the least count (accuracy) of different instruments: 0.1 mm for vernier calipers and 0.01 mm for screw gauges. This knowledge helps in selecting the right tool.

IV. Match the following:

 

Question 1.

Answer:In simple words: This matching exercise connects fundamental physical quantities with their correct SI units. Length is measured in meters, mass in kilograms, time in seconds, and temperature in kelvin. These are the basic units we use in science.

🎯 Exam Tip: Knowing the base SI units for fundamental quantities is crucial for all physics problems. Practice recalling them quickly.

 

Question 2.

Answer:In simple words: This match helps us understand which tool is best for measuring different objects. A screw gauge is very precise for tiny things like gold ornaments. A vernier caliper is good for small items like coins. A beam balance is used for common items such as vegetables, and a digital balance can measure something like a cricket ball.

🎯 Exam Tip: Relate each measuring instrument to its appropriate use based on its precision and the type of object being measured.

V. Assertion and reason type :

 

Question 1. Assertion (A) : The scientifically correct expression is "The mass of the bag is 10 kg" Reason (R) : In everyday life, we use the term weight instead of mass.
(a) Both A and R are true but R is not the correct reason.
(b) Both A and R are true and R is the correct reason.
(c) A is true but R is false.
(d) A is false but R is true
Answer: (a) Both A and R are true but R is not the correct reason.
In simple words: Both the assertion and the reason are true statements by themselves. However, the reason about common language use does not explain *why* saying "mass is 10 kg" is scientifically correct. The scientific correctness comes from mass being a fundamental quantity, while weight is a force.

🎯 Exam Tip: In assertion-reason questions, first check if both statements are individually true. Then, check if the reason correctly explains the assertion.

 

Question 2. Assertion (A) : \( 0^\circ \text{C} = 273.16 \text{ K} \). For our convenience we take it as 273K after rounding off the decimal. Reason (R) : To convert a temperature on the Celsius scale we have to add 273 to the given temperature.
(a) Both A and R are true but R is not the correct explanation of A.
(b) Both A and R are true and R is the correct reason
(c) A is true but R is false. .
(d) A is false but R is true
Answer: (b) Both A and R are true and R is the correct reason
In simple words: The assertion states the correct conversion from Celsius to Kelvin and explains why we often round it. The reason gives the rule for this conversion, which directly supports and explains the assertion. This makes it a correct pair.

🎯 Exam Tip: Understand the exact relationship between Celsius and Kelvin: \( \text{K} = ^\circ \text{C} + 273.15 \). The rounding is a practical simplification.

 

Question 3. Assertion (A) : Distance between two celestial bodies is measured in terms of light year. Reason (R) : The distance travelled by the light in one year is one light year.
(d) A is false but R is true
Answer: (d) A is false but R is true
In simple words: The assertion is false because light-year is a unit of distance, but it is incorrect to say that distance *between* two celestial bodies is *only* measured in light years. It can also be measured in Astronomical Units or parsecs. The reason, however, correctly defines a light-year as the distance light covers in one year. Light travels at an incredibly high speed.

🎯 Exam Tip: Pay close attention to absolute statements like "is measured in terms of" versus "can be measured in terms of". "Light year" is a unit of distance, not time.

VI. Answer very briefly.

 

Question 1. Define measurement.
Answer: Measurement is the process of comparing a physical quantity we want to know with a known standard quantity of the same kind. This process helps us find out how big, long, or heavy something is. For example, measuring a table's length with a meter stick.
In simple words: Measurement is when we compare something we want to measure (like length) to a known amount of the same thing (like a meter).

🎯 Exam Tip: Use keywords like "comparison," "physical quantity," and "known standard quantity" in your definition for full marks.

 

Question 2. Define a standard unit.
Answer: A standard unit is a fixed quantity of a constant size that is used to measure the sizes of other similar quantities. It must be consistent and universally accepted, like the meter for length or the kilogram for mass.
In simple words: A standard unit is a fixed amount (like 1 meter) that we use to measure other things of the same type.

🎯 Exam Tip: Emphasize "constant magnitude" and "used to measure other quantities" in your definition of a standard unit.

 

Question 3. What is the full form of SI system?
Answer: The full form of the S.I. system is the International System of Units. This system is used all over the world to make sure everyone measures things in the same way.
In simple words: SI stands for "International System of Units."

🎯 Exam Tip: Remember that "SI" comes from the French "Système International d'Unités" but is commonly known in English as the International System of Units.

 

Question 4. Define least count of any device.
Answer: The least count of any measuring device is the smallest measurement that can be accurately taken with that device. For example, a ruler might have a least count of 1 millimeter. For a screw gauge, it is given by:
Least count \( = \frac{\text{Pitch}}{\text{No. of head scale divisions}} \). This value tells us how precise the instrument is.
In simple words: The least count is the smallest thing a measuring tool can measure correctly.

🎯 Exam Tip: Always state that the least count represents the *minimum* accurate measurement possible with an instrument and include its formula if applicable.

 

Question 5. What do you know about pitch of screw gauge?
Answer: The pitch of a screw gauge is the distance the screw moves along its main scale when it completes one full rotation. It is also found by dividing the distance moved on the pitch scale by the number of rotations of the head scale. This value is important for calculating the least count.
In simple words: The pitch of a screw gauge is how far the screw moves forward when you turn it around one full time.

🎯 Exam Tip: Define pitch clearly as the linear distance moved for one full rotation, and its relation to the pitch scale and head scale rotations.

 

Question 6. Can you find the diameter of a thin wire of length 2 m using the ruler from your instrument box?
Answer: No, I cannot find the diameter of a thin wire of length 2 m using a ruler. A ruler is not precise enough to measure the tiny diameter of a thin wire accurately, even if the wire is long. Specialized tools like a screw gauge are needed for such small measurements.
In simple words: No, a ruler cannot measure how thick a thin wire is because it's not precise enough for such small sizes.

🎯 Exam Tip: Highlight the limitation of a ruler for very small measurements and suggest appropriate instruments like a screw gauge.

VII. Answer briefly :

 

Question 1. Write the rules that are followed in writing the symbols of units in SI system.
Answer: Here are the rules for writing unit symbols in the SI system:

• The symbols for units named after scientists are written with a capital initial letter (e.g., N for newton, H for henry, A for ampere, W for watt).
• Units not named after scientists use small letters as symbols (e.g., m for metre, kg for kilogram).
• No full stop or other punctuation marks should be used within or at the end of symbols (e.g., 50 m, not 50 m.).
• The symbols of the units are not expressed in plural form (e.g., 10 kg, not 10 kgs).

These rules ensure clear and consistent communication in science.
In simple words: When writing unit symbols, use a capital letter if it's named after a scientist (like N for Newton), otherwise use a small letter (like m for meter). Don't add a period or make them plural.

🎯 Exam Tip: List at least three of these rules accurately, focusing on capitalization, punctuation, and pluralization, as they are common areas of error.

 

Question 2. Write the need of a standard unit.
Answer: A standard unit is needed to ensure that measurements are consistent and uniform everywhere, regardless of who is measuring or where. This means everyone gets the same result for a given quantity. For example, the standard unit of length is the metre, which allows us to compare lengths accurately across the globe.
In simple words: We need standard units so everyone measures things the same way, everywhere, and gets the same answer.

🎯 Exam Tip: Focus on "uniformity" and "consistency in measurements" as the primary reasons for standard units.

 

Question 3. Differentiate mass and weight.
Answer:

Mass:

1. It is a fundamental quantity.
2. It has magnitude alone, making it a scalar quantity.
3. Mass is the amount of matter an object contains.
4. It remains the same regardless of location.
5. It is measured using a physical balance or beam balance.
6. Its SI unit is kilogram (kg).

Weight:

1. It is a derived quantity.
2. It has both magnitude and direction, making it a vector quantity.
3. Weight is the normal force exerted by a surface on an object against gravitational pull.
4. It changes from place to place, depending on gravity.
5. It is measured using a spring balance.
6. Its SI unit is newton (N).

Understanding these differences is key in physics.
In simple words: Mass is how much stuff is in an object and stays the same everywhere, measured in kilograms. Weight is how hard gravity pulls on an object and changes with location, measured in newtons.

🎯 Exam Tip: Clearly list distinguishing points for both mass and weight, covering their nature (fundamental/derived), type (scalar/vector), definition, constancy, measuring instrument, and SI unit.

 

Question 4. How will you measure the least count of vernier caliper?
Answer: The least count of a Vernier caliper is found by taking the ratio of the value of one smallest main scale division to the total number of divisions on the Vernier scale.
Least Count \( = \frac{\text{Value of one smallest main scale division}}{\text{Total number of Vernier scale divisions}} \). For example, if 1 Main Scale Division (MSD) is 1mm and there are 10 Vernier Scale Divisions (VSD), then LC = 1mm/10 = 0.1mm. Alternatively, it can be calculated as LC \( = 1 \text{ MSD} - 1 \text{ VSD} \). If 1 MSD is 1.0 mm and 1 VSD is 0.9 mm, then LC = 1.0 mm - 0.9 mm = 0.1 mm.
In simple words: To find the least count of a vernier caliper, you divide the smallest part of the main scale by the total number of parts on the vernier scale. This tells you the smallest accurate measurement it can make.

🎯 Exam Tip: Provide both common formulas for least count and explain what each term means to ensure clarity and completeness.

VIII. Answer in detail :

 

Question 1. Explain a method to find the thickness of a hollow teacup.
Answer: To find the thickness of a hollow teacup using a screw gauge, follow these steps:

1. First, determine the pitch, least count, and any zero error of the screw gauge.
2. Place the teacup between the two studs of the screw gauge.
3. Rotate the head screw using the ratchet mechanism until the cup is held firmly but not too tightly.
4. Note down the Pitch Scale Reading (PSR) and the Head Scale Coincidence (HSC) with the pitch scale axis.
5. Record these readings and repeat the experiment for different positions on the cup to ensure accuracy.
6. Calculate the thickness of the cup using the formula: Total Reading \( = \text{P.S.R} + (\text{HSC} \times \text{L.C}) \).
7. Finally, find the average of all the readings to get the most accurate thickness of the hollow teacup. This careful process helps get a precise measurement.

In simple words: To measure a teacup's thickness, first check the screw gauge settings. Then, gently place the cup in the gauge and tighten it. Write down the main scale and head scale readings. Repeat a few times, then use a formula to find the thickness. Finally, average your answers for the best result.

🎯 Exam Tip: Present the method as clear, numbered steps. Include the formula for total reading and mention the importance of repeating measurements for accuracy.

 

Question 2. How will you find the thickness of a one rupee coin?
Answer: To find the thickness of a one-rupee coin using a screw gauge, follow these steps:

1. First, determine the pitch, least count, and the type of zero error of the screw gauge.
2. Place the coin between the two studs of the screw gauge.
3. Rotate the head screw using the ratchet arrangement until the coin is held firmly, but not tightly.
4. Note down the Pitch Scale Reading (PSR) and the Head Scale Coincidence (HSC) with the pitch scale axis.
5. Record these readings and repeat the experiment for different positions on the coin to ensure accuracy.
6. Calculate the thickness of the coin using the formula: Total Reading \( = \text{P.S.R} + (\text{HSC} \times \text{L.C}) \).
7. Finally, find the average of all the readings from the last column of your table. This average will be the thickness of the one-rupee coin.

This method helps achieve an accurate measurement of small objects.
In simple words: To find the thickness of a coin, first set up the screw gauge and check for any errors. Place the coin in the gauge and gently close it. Read the main scale and the head scale. Do this a few times, then use the formula to get the thickness. Finally, average all your thickness values.

🎯 Exam Tip: Clearly outline the steps for using a screw gauge, including how to take readings and the formula for calculating total reading, along with the need for multiple readings and averaging.

IX. Numerical Problems :

 

Question 1. Inian and Ezhilan argue about the light year. Inian tells that it is \( 9.46 \times 10^{15} \text{m} \) and Ezhilan argues that it is \( 9.46 \times 10^{12} \text{ km} \). Who is right? Justify your answer.
Answer: Inian is correct.

Here's why:

Light travels at a speed of \( 3 \times 10^8 \text{ m/s} \) (or 3 Lakhs kilometers per second) in one second.

In one year, there are 365 days.

The total number of seconds in one year is \( 365 \times 24 \times 60 \times 60 \text{ seconds} \).

Distance travelled by light in 1 year \( = (3.153 \times 10^7) \times (3 \times 10^8) \)

\( = 9.46 \times 10^{15} \text{ m} \).

This shows that Inian's value is accurate. A light-year is a vast distance.
In simple words: Inian is right. A light-year is how far light travels in one year. When you calculate this using the speed of light and the number of seconds in a year, the distance comes out to \( 9.46 \times 10^{15} \) meters.

🎯 Exam Tip: Clearly show the steps for calculating the number of seconds in a year and then use the speed of light to find the distance, ensuring correct powers of ten.

 

Question 2. The main scale reading while measuring the thickness of a rubber ball using Vernier caliper is 7 cm and the Vernier scale coincidence is 6. Find the radius of the ball.
Answer: Given:

Main Scale Reading (MSR) \( = 7 \text{ cm} \)

Vernier Scale Coincidence (VC) \( = 6 \)

Least Count (LC) of Vernier caliper \( = 0.1 \text{ mm} = 0.01 \text{ cm} \)

Diameter (DR) \( = \text{MSR} + (\text{VC} \times \text{LC}) \)

\( = 7 \text{ cm} + (6 \times 0.01 \text{ cm}) \)

\( = 7 + 0.06 \text{ cm} \)

Diameter D \( = 7.06 \text{ cm} \)

Radius R \( = \frac{\text{D}}{2} \)

\( = \frac{7.06}{2} \text{ cm} = 3.53 \text{ cm} \)

To convert to meters: \( = 0.0353 \text{ m} \)

The radius of the ball is \( 0.0353 \text{ m} \).
In simple words: We used the main scale reading, the Vernier scale coincidence, and the least count to find the ball's diameter. Then, we divided the diameter by two to get the radius. The final radius is 0.0353 meters.

🎯 Exam Tip: Always convert all units to be consistent (e.g., cm or m) before performing calculations. Remember that radius is half the diameter.

 

Question 3. Find the thickness of a five rupee coin with the screw gauge, if the pitch scale reading is 1 mm and its head scale coincidence is 68.
Answer: Given:

Pitch Scale Reading (PSR) \( = 1 \text{ mm} = 1 \times 10^{-3} \text{ m} \)

Head Scale Coincidence (HSC) \( = 68 \)

Least Count (LC) of screw gauge \( = 0.01 \text{ mm} = 0.01 \times 10^{-3} \text{ m} \)

Total reading \( = \text{PSR} + (\text{HSC} \times \text{LC}) \)

Thickness of the five rupee coin \( = 1 \times 10^{-3} \text{ m} + (68 \times 0.01 \times 10^{-3} \text{ m}) \)

\( = 1 \times 10^{-3} \text{ m} + (0.68 \times 10^{-3} \text{ m}) \)

\( = (1 + 0.68) \times 10^{-3} \text{ m} \)

\( = 1.68 \times 10^{-3} \text{ m} \)

\( = 1.68 \text{ mm} \)

So, the thickness of the five rupee coin is \( 1.68 \text{ mm} \).
In simple words: To find the coin's thickness, we add the pitch scale reading to the head scale reading multiplied by the least count. This formula helps us combine the different scale readings to get one precise measurement.

🎯 Exam Tip: Ensure you use the correct least count for the screw gauge (typically 0.01 mm) and perform calculations with consistent units (e.g., all in meters or all in millimeters).

 

Question 4. Find the mass of an object weighing 98 N.
Answer: Given:

Weight (W) \( = 98 \text{ N} \)

We know that weight \( \text{W} = \text{m} \times \text{g} \), where 'm' is mass and 'g' is acceleration due to gravity.

Acceleration due to gravity (g) \( = 9.8 \text{ m/s}^2 \)

Rearranging the formula to find mass: \( \text{m} = \frac{\text{W}}{\text{g}} \)

\( \text{m} = \frac{98 \text{ N}}{9.8 \text{ m/s}^2} \)

\( \text{m} = 10 \text{ kg} \)

Thus, the mass of the object is \( 10 \text{ kg} \).
In simple words: To find the mass, we divide the object's weight by the force of gravity. Since weight is 98 N and gravity is 9.8 m/s\( ^2 \), the mass comes out to be 10 kg.

🎯 Exam Tip: Remember the formula \( \text{W} = \text{mg} \) and the standard value of \( \text{g} \approx 9.8 \text{ m/s}^2 \). Pay attention to units for a correct final answer.

Intext Activities

ACTIVITY - 1

 

Question. Using Vernier caliper find the outer diameter of your pen cap.
Answer: Aim: To find the outer diameter of the pen cap.

Materials required: Vernier caliper, pen cap.

Result: The outer diameter of the pen cap \( = 9.35 \text{ cm} \).

This activity shows how a vernier caliper is used to measure small dimensions accurately.
In simple words: To measure the pen cap's outer diameter, we use a vernier caliper. We take a few readings from its main scale and vernier scale, then calculate the diameter for each. Finally, we average these diameters to get the most accurate answer.

🎯 Exam Tip: When performing practical experiments, record data systematically in a table. Always calculate an average of multiple readings to minimize random errors.

Activity -2

Determine the thickness of a single sheet of your science textbook with the help of a Screw gauge.

Mean thickness 't' of the sheet = 0.30

LC = Least Count
PSR = Pitch Scale Reading
HSC = Head Scale Coincidence
HSR = Head Scale Reading
TR = Total Reading
Result : The thickness of the single sheet = 0.30
End of the activity

9th Science Guide Measurement Additional Important Questions And Answers

I. Choose The Correct Answer :

 

Question 1. Length is ....................
(a) The amount of matter in an object
(b) The amount of space an object takes up.
(c) The distance between two points.
(d) The amount of stuff in an object
Answer: (c) The distance between two points
In simple words: Length measures how far apart two points are. It helps us know the size or extent of something.

🎯 Exam Tip: Remember that length is a fundamental quantity, representing a spatial dimension.

 

Question 2. Mass is ....................
(a) The distance between two points
(b) The distance between three points
(c) The amount of matter contained in an object
(d) The amount of space an object occupies.
Answer: (c) The amount of matter contained in an object
In simple words: Mass tells us how much "stuff" or material an object is made of. It is a basic property of matter.

🎯 Exam Tip: Do not confuse mass with weight; mass is constant, while weight depends on gravity.

 

Question 3. Unit used to measure length
(a) metre
(b) litre
(c) gram
(d) cubic metre (m³)
Answer: (a) metre
In simple words: The standard unit for measuring length is the metre. We use it to measure things like the height of a building or the distance of a jump.

🎯 Exam Tip: Understand the common units for fundamental quantities (metre for length, kilogram for mass, second for time) as these are frequently asked.

 

Question 4. Unit which is used to measure mass
(a) ml
(b) 1
(c) cm
(d) gram
Answer: (d) gram
In simple words: Gram is a unit used to measure mass. We often use grams for lighter items, like the mass of a small fruit.

🎯 Exam Tip: Be familiar with both SI units (kilogram for mass) and commonly used units like gram, understanding their conversions.

 

Question 5. How many metres are there in 1 nanometer?
(a) \( 10^{-10} \)m
(b) \( 10^{-9} \)m
(c) \( 10^9 \)m
(d) \( 10^{10} \)m
Answer: (b) \( 10^{-9} \)m
In simple words: A nanometer is a very tiny unit of length, so small that it takes one billion nanometers to make just one metre. This means 1 nanometer is \( 10^{-9} \) metres.

🎯 Exam Tip: Memorize common prefixes for units (nano-, micro-, milli-, centi-, kilo-) and their corresponding powers of 10 for quick conversions.

 

Question 6. What unit will you use to measure the length of our classroom?
(a) km
(b) m
(c) cm
(d) mm
Answer: (b) m
In simple words: For measuring something like a classroom, metres are the most suitable unit. Kilometres are too big, and centimetres or millimetres are too small.

🎯 Exam Tip: Choose the unit that gives a convenient and easily understandable numerical value for the measurement being made.

 

Question 7. The Kelvin is the basic unit of ....................
(a) temperature
(b) mass
(c) length
(d) volume
Answer: (a) temperature
In simple words: Kelvin is the fundamental unit for measuring temperature in the SI system. It starts from absolute zero, where particles have the least possible energy.

🎯 Exam Tip: Know the seven base SI units and what physical quantity each measures. Kelvin is crucial for scientific calculations.

 

Question 8. .................... consists of 'U' shape metal frame
(a) Screw gauge
(b) Vernier caliper
(c) Beam balance
(d) Spring balance
Answer: (a) screw gauge
In simple words: A screw gauge is a tool with a U-shaped metal frame, used for very precise measurements of small lengths, like the thickness of a wire. This design helps hold objects steady for accurate readings.

🎯 Exam Tip: Visualizing the instrument can help remember its key features and what it is used for, especially its U-shaped frame.

 

Question 9. Least count of a vernier caliper is .................... cm.
(a) 1
(b) 0.1
(c) 0.01
(d) 0.001
Answer: (c) 0.01
In simple words: The least count of a vernier caliper is 0.01 cm, which means it can measure very small lengths up to two decimal places in centimetres. This precision makes it useful for small objects.

🎯 Exam Tip: Always remember the least count of common measuring instruments as it indicates their precision. For vernier calipers, it's typically 0.01 cm or 0.1 mm.

 

Question 10. If no object is placed on the hook, then the pointer of the spring balance reads ....................
(a) 3
(b) 2
(c) 1
(d) 0
Answer: (d) 0
In simple words: When nothing is weighing down a spring balance, its pointer should show zero. This indicates that there is no force or weight being measured.

🎯 Exam Tip: Always check for the zero error in any measuring instrument before use, ensuring it reads zero when nothing is being measured.

 

Question 11. SI unit of mass and weights are ....................
(a) kg, N
(b) N, kg
(c) K, N
(d) N, K
Answer: (a) kg, N
In simple words: The SI unit for mass is the kilogram (kg), and the SI unit for weight, which is a force, is the Newton (N). It's important to differentiate these two quantities and their units.

🎯 Exam Tip: Clearly distinguish between mass (amount of matter, unit kg) and weight (force due to gravity, unit N), as they are distinct concepts often confused.

 

Question 12. Units named after scientists ....................
(a) lowercase
(b) upper case
(c) both (a) and (b)
(d) neither (a) or (b)
Answer: (a) lowercase
In simple words: When writing the full name of a unit named after a scientist (like newton or ampere), we use a lowercase letter. However, if we write its symbol, we use an uppercase letter (N, A).

🎯 Exam Tip: Pay attention to the capitalization rules for SI units: full name is lowercase (e.g., ampere), but its symbol is uppercase if derived from a proper name (e.g., A).

 

Question 13. An instrument that is used to measure the diameter of a cricket ball is ....................
(a) Screw gauge
(b) Meter scale
(c) Vernier caliper .
(d) Spring balance
Answer: (a) Vernier caliper
In simple words: A vernier caliper is the best tool to measure the diameter of a cricket ball. It provides more accuracy than a simple meter scale, while a screw gauge is usually for even smaller objects like thin wires.

🎯 Exam Tip: Choose the appropriate measuring instrument based on the size and required precision of the object being measured.

 

Question 14. Distance between Chennai and Kanyakumari can be found in
(a) Kilometres
(b) Metres
(c) Centimetres
(d) Millimetres.
Answer: (a) Kilometres
In simple words: To measure long distances, like between two cities, we use kilometres. This unit is practical for large geographical spans.

🎯 Exam Tip: Select the most appropriate unit for the scale of the measurement. Kilometres are ideal for inter-city distances.

II. Fill In The Blanks :

 

1. The precision of vernier calipers is .................... mm.
Answer: 0.1
In simple words: A vernier caliper can measure very precisely, detecting differences as small as 0.1 millimetres. This makes it good for getting exact sizes.

🎯 Exam Tip: Remember the least count (precision) of vernier calipers is 0.1 mm or 0.01 cm, which is crucial for calculations involving this instrument.

 

2. The gravity accelerates an object, the distance fallen is proportional to ....................
Answer: time squared
In simple words: When an object falls because of gravity, the distance it covers is related to the square of the time it has been falling. This means if it falls for twice the time, it falls four times the distance.

🎯 Exam Tip: Understand the kinematic equations, especially for free fall, where distance is proportional to the square of time ( \( d = \frac{1}{2}gt^2 \) ).

 

3. SI unit of electric current is ....................
Answer: ampere
In simple words: The standard unit for measuring electric current is the ampere. It tells us how much electric charge flows past a point each second.

🎯 Exam Tip: Ensure you know all seven base SI units and their corresponding physical quantities. Ampere is fundamental for electricity.

 

4. Larger unit for measuring time is ....................
Answer: millennium
In simple words: While seconds and minutes are common for short periods, a millennium is a much larger unit, representing one thousand years. It's used to talk about very long stretches of history.

🎯 Exam Tip: Be aware of various units of time and their magnitudes, from seconds to millennia, and when each is appropriate to use.

 

5. The value of an astronomical unit is ....................
Answer: \( 1.496 \times 10^{11} \)
In simple words: An astronomical unit (AU) is a very large distance, about 150 million kilometres. It's mainly used to measure distances within our solar system, like the distance from Earth to the Sun.

🎯 Exam Tip: Understand what an astronomical unit (AU) represents and its approximate value, as it's a key unit for astronomical distances.

 

6. Mass is a .................... quantity.
Answer: scalar
In simple words: Mass is a scalar quantity, meaning it only has a size or amount, but no direction. For example, a 5 kg bag of rice just has a mass of 5 kg, not "5 kg to the east".

🎯 Exam Tip: Differentiate between scalar quantities (magnitude only, e.g., mass, time, speed) and vector quantities (magnitude and direction, e.g., force, velocity, displacement).

III. State Whether True Or False. If False, Correct The Statement:

 

1. The precision of screw gauge is 0.001 cm.
Answer: True.
In simple words: A screw gauge is a very accurate tool that can measure lengths as small as 0.001 centimetres. This level of precision is needed for measuring extremely thin objects.

🎯 Exam Tip: Know the least count of a screw gauge (0.01 mm or 0.001 cm) and compare it to that of a vernier caliper to understand its higher precision.

 

2. The unit of amount of substance is candela
Answer: False.
Correct statement: The unit of amount of substance is mole.
In simple words: The unit "mole" is used to measure the amount of a substance, like counting how many particles are there. Candela, on the other hand, is for measuring how bright a light source is.

🎯 Exam Tip: Ensure you correctly associate each physical quantity with its standard SI unit to avoid common errors.

 

3. The symbol for the units derived from the names of scientists are written in capital letter
Answer: True.
In simple words: If a unit's symbol comes from a scientist's name, like 'N' for Newton or 'A' for Ampere, it is always written with a capital letter. This is a common rule in the SI system.

🎯 Exam Tip: Differentiate between the full unit name (lowercase) and its symbol (uppercase if named after a person) to follow correct scientific notation.

 

4. Yard was used as the unit of length.
Answer: True
In simple words: A yard is an old unit of length, similar to a metre. It was commonly used in the past, especially in countries like England, for measuring distances.

🎯 Exam Tip: Be aware of both modern SI units and historical units of measurement, understanding their context and approximate equivalents.

 

5. Micron is also known as micro-metre
Answer: True
In simple words: A micron is just another name for a micrometer. Both terms mean one-millionth of a metre, used for measuring very small things like cells.

🎯 Exam Tip: Recognize common alternative names for units and prefixes, as they often refer to the same measurement.

 

6. A vernier caliper using the scale invented by Galileo.
Answer: False.
Correct statement: A vernier caliper using the scale invented by Pierre Vernier.
In simple words: The vernier scale, which is the key part of a vernier caliper, was actually invented by Pierre Vernier. Galileo invented other scientific tools, but not this one.

🎯 Exam Tip: Knowing the historical context and the inventors of key scientific instruments can help in true/false questions and general knowledge.

 

7. The SI unit of mass is kg.
Answer: True.
In simple words: The kilogram (kg) is the official unit for mass in the International System of Units. We use it worldwide to measure how much matter an object contains.

🎯 Exam Tip: Remember that kilogram is the only base SI unit with a prefix (kilo-); all other base units are fundamental without prefixes.

 

8. Weight has both magnitude and direction.
Answer: True.
In simple words: Weight is a force, so it has both a size (how strong the pull of gravity is) and a direction (always pointing downwards towards the center of the Earth). This makes it a vector quantity.

🎯 Exam Tip: Understand that weight is a vector because it is a force, always acting in the direction of gravity, unlike scalar mass.

IV. Match The Following:

 

Question 1.

Answer:In simple words: This match-up connects each basic physical quantity with its standard SI unit. Length is measured in metres, mass in kilograms, time in seconds, and temperature in kelvin.

🎯 Exam Tip: Thoroughly memorize the seven fundamental SI quantities and their corresponding units, as they form the basis of most physical measurements.

 

Question 2.

Answer:In simple words: This table explains different systems of units. FPS uses foot, pound, and second; CGS uses centimetre, gram, and second; and MKS, which is the basis for SI, uses metre, kilogram, and second. Each system has its own set of base units for length, mass, and time.

🎯 Exam Tip: Understand the historical evolution and key differences between FPS, CGS, and MKS systems, which led to the modern SI system.

 

Question 3.

Answer:In simple words: This section matches different periods of time with their correct names. 10 years make a decade, 10 centuries make a millennium, 10 decades make a century, and 365.24 days make one year (accounting for leap years).

🎯 Exam Tip: Be precise with time conversions; know the exact number of years in a decade, century, and millennium, and the number of days in a year.

 

Question 4.

Answer:In simple words: This match connects various physical quantities with their correct SI or derived units. Electric current is measured in amperes, luminous intensity in candelas, plane angle in radians, and solid angle in steradians.

🎯 Exam Tip: Pay special attention to supplementary units like radian and steradian, and differentiate them from base units.

 

Question 5.

Answer:In simple words: This section correctly pairs fundamental physical quantities with their standard SI unit symbols. Length uses 'm' for metre, mass uses 'kg' for kilogram, time uses 's' for second, and temperature uses 'k' for kelvin.

🎯 Exam Tip: Familiarize yourself with the exact symbols for all SI units to avoid confusion, especially with capitalization rules.

 

Question 6.

Answer:In simple words: This match-up clarifies how different small units of length relate to the metre. A millimetre is \( 10^{-3} \) m, a nanometer is \( 10^{-9} \) m, an Angstrom is \( 10^{-10} \) m, and a Fermi (or femtometre) is \( 10^{-15} \) m. These prefixes help describe very tiny sizes accurately.

🎯 Exam Tip: Accurately recall the powers of 10 for various prefixes (milli-, nano-, Angstrom, femto-) to perform unit conversions correctly.

 

Question 7.

Answer:In simple words: This section pairs common physical quantities with the instruments used to measure them. A thermometer measures temperature, a beam balance measures mass, a ruler measures length, and a digital clock measures time. Each tool is designed for a specific type of measurement.

🎯 Exam Tip: Understand the correct instrument for measuring each physical quantity; this is fundamental for practical science and problem-solving.

V. Assertion And Reason Type :

 

Question 1. Assertion (A): Light year and wave length both measure distance Reason (R) : Both have dimensions of time.
(a) Both A and R are true but R is not the correct explanation of A.
(b) Both A and R are true and R is the correct explanation of A.
(c) A is true but R is false.
(d) A is false but R is true.
Answer: (c) A is true but R is false.
In simple words: Assertion (A) is correct because both light-year and wavelength are units of distance. However, Reason (R) is false because neither light-year nor wavelength has dimensions of time; they both measure length.

🎯 Exam Tip: Always analyze Assertion (A) and Reason (R) independently for truthfulness first, then determine if R correctly explains A. Pay close attention to the dimensions of physical quantities.

 

Question 2. Assertion (A) : Density is a derived physical quantity Reason (R) : Density cannot be derived from the fundamental physical quantities.
(a) Both A and R are true but R is not the correct explanation of A.
(b) Both A and R are true and,R-is the correct explanation of A.
(c) A is true but R is false. .
(d) A is false but R is true.
Answer: (c) A is true but R is false.
Correct statement: Density can be derived from mass and volume.
In simple words: Assertion (A) is true because density comes from combining mass and volume, which are more basic. Reason (R) is false because density *can* be found from fundamental quantities (mass, length for volume).

🎯 Exam Tip: Remember that derived quantities are those that can be expressed in terms of fundamental (base) quantities through mathematical operations.

 

Question 3. Assertion (A) : Mass, Length and Time are fundamental physical quantities. Reason (R) : They are independent of each other.
(a) Both A and R are true but R is not the correct explanation of A.
(b) Both A and R are true and R is the correct explanation of A.
(c) A is true but R is false.
(d) A is false but R is true.
Answer: (b) Both A and R are true and R is the correct explanation of A
In simple words: Assertion (A) is true because mass, length, and time are basic building blocks of measurements. Reason (R) is also true, and it correctly explains why they are fundamental: you cannot define one using the others, they are separate.

🎯 Exam Tip: Fundamental quantities are defined independently and form the basis for all other derived quantities in a system of units.

 

Question 4. Assertion (A): The SI system of units is the improved system of units for measurement. Reason (R) : The SI unit of mass is kilogram.
(a) Both A and R are true but R is not the correct reason.
(b) Both A and R are true and R is the correct reason.
(c) A is true but R is false.
(d) A is false but R is true.
Answer: (b) Both A and R are true and R is the correct reason
In simple words: Assertion (A) is true because the SI system is a modern and improved way to measure things globally. Reason (R) is also true, stating that the kilogram is the SI unit of mass, which is one example of what makes SI a coherent system.

🎯 Exam Tip: The SI system is widely adopted due to its coherence, rationality, and convenience, making it the standard for scientific and technical work.

 

Question 4. Assertion (A): The SI system of units is the improved system of units for measurement.
Reason (R): The SI unit of mass is kilogram.
(a) Both A and R are true but R is not the correct reason.
(b) Both A and R are true and R is the correct reason.
(c) A is true but R is false.
(d) A is false but R is true.
Answer: (b) Both A and R are true and R is the correct reason
In simple words: Both the statement that SI system is improved and that the SI unit of mass is kilogram are true. The kilogram being the SI unit of mass is a correct reason for the SI system being improved, as it provides a consistent, standardized approach to measurement.

🎯 Exam Tip: For assertion-reason questions, first check if both statements are individually true. Then, check if the reason logically explains the assertion.

 

Question 5. Assertion (A): The skill of estimation is important for all of us in our daily life.
Reason (R): The skill of estimation reduces our consumption of time.
(a) Both A and R are true but R is not the correct reason.
(b) Both A and R are true and R is the correct reason.
(c) A is true but R is false.
(d) A is false but R is true.
Answer: (b) Both A and R are true and R is the correct reason
In simple words: It is true that estimating things helps us every day. This is because making a quick guess helps us save time when exact measurements are not needed.

🎯 Exam Tip: Estimation skills are valuable in many real-world scenarios, from budgeting to planning, as they allow for quick decisions without precise calculations.

VI. Comprehensive Type

(a) The speed of a body gives us an idea of how slow or fast that a body is moving. Speed of a body is the distance travelled by it per unit time. The SI unit of speed is metre per second. It is a scalar quantity. The speed of a running cab at any instant of time is shown by an instrument called, 'speedometer' and the distance travelled by a car is measured by another instrument called, 'odometer'.

 

Question 1. Which of the following is not a correct unit of speed?
(a) cm/s
(b) m/s
(c) km/h
(d) km/s.
Answer: (d) km/s
In simple words: Speed is usually measured as distance divided by time. Kilometers per second (km/s) is a common unit for very fast speeds, like those in space, but the question lists 'e) km/h' so (d) is an error. The given options (a), (b), (c) are all valid units of speed in different contexts. However, `km/s` is indeed a unit of speed. Based on the options and the likely intent (finding a non-standard or incorrect one *if* the given options were meant to represent standard choices), there might be an issue with the question itself or the provided options. Given that `km/s` is a legitimate unit, if there's an expectation for only one 'incorrect' answer, this would imply an error in the question or the provided options/answer. If we consider the context of common, everyday speeds for a running cab, `km/s` would be an unusually large unit, but not technically incorrect. The original text lists (e) km/h, but the options are (a) to (d). Assuming a typo in the question and 'e' was meant to be 'c' and 'd' was meant to be the answer. Reinterpreting based on the provided answer, `km/s` is stated as the incorrect unit. This suggests it might be considered an "incorrect" unit in the context of typical classroom examples of speed, or a specific curriculum definition, although physically it is valid. For a cab, cm/s, m/s, km/h are more practical units. Km/s is usually for much higher speeds.

🎯 Exam Tip: Always pay attention to the context of the question. While physically valid, `km/s` is not a common unit for a "running cab," suggesting it might be the intended "incorrect" option in an options list aiming for practical relevance.

 

Question 2. If the distance travelled by the cab in 3 hours is 120 km, then its speed will be
(a) 40 m/s
(b) 40 km/s
(c) 40 km/h
(d) 40 km/min
Answer: (c) 40 km/h
In simple words: To find the speed, divide the total distance by the time taken. If the cab travels 120 km in 3 hours, its speed is 120 divided by 3, which is 40 km/h.

🎯 Exam Tip: Remember the basic formula for speed: Speed = Distance / Time. Pay attention to the units requested in the options and convert if necessary.

 

Question 3. The formula for finding the speed of the cab is
(a) Distance = speed x time
(b) velocity = distance x time
(c) time = distance x velocity
(d) None of the options.
Answer: (a) Distance = speed x time
In simple words: Speed is found by dividing distance by time. If you rearrange this, you get that distance equals speed multiplied by time. This is a fundamental relationship in motion.

🎯 Exam Tip: Memorize the three forms of the speed, distance, and time relationship: Speed = Distance/Time, Distance = Speed x Time, Time = Distance/Speed.

(b) Read the passage and answer the questions given below. Mass is the amount of matter contained in an object. Measurement of mass helps us to distinguish between lighter and a heavier body. Beam-Balance, spring balance and electronic balance are used to measure mass of different objects.

 

Question 1. The value of 1 metric ton is equal to
(a) 1000 kg
(b) 10 quintals
(c) 1,000,000 g
(d) 100 kg
Answer: (a) 1000 kg (or) (b) 10 quintals
In simple words: One metric ton is the same as 1000 kilograms. It also equals 10 quintals, where one quintal is 100 kg. This means both options (a) and (b) are correct ways to express one metric ton.

🎯 Exam Tip: Know common unit conversions for mass (like tons to kg, quintals to kg) as these are frequently tested in basic science and math problems.

 

Question 2. How will you measure weight of a tablet?
(a) kg
(b) g
(c) mg
(d) None of the options.
Answer: (c) mg
In simple words: A tablet is very light, so its mass is best measured in milligrams (mg), which is a very small unit of mass. This allows for precise measurement.

🎯 Exam Tip: Choose the appropriate unit of measurement based on the size or quantity of the object. Small items like tablets use milligrams, while larger items use grams or kilograms.

VII. Answer Very Briefly :

 

Question 1. Write the units which are used to measure long distances.
Answer: To measure very long distances, especially in space, we use units like kilometers (km), Astronomical Units (AU), light-years, and parsecs. Each unit is suitable for increasingly vast distances. For instance, AU is good for distances within our solar system.
In simple words: For long distances, we use kilometers, Astronomical Units (AU), light-years, and parsecs.

🎯 Exam Tip: Remember that light-year is a unit of distance, not time. It represents the distance light travels in one year.

 

Question 2. Define Astronomical unit.
Answer: An Astronomical Unit (AU) is defined as the average distance between the Earth and the Sun. This average distance is approximately \( 1.496 \times 10^{11} \text{ m} \). It is a convenient unit for measuring distances within our solar system.
In simple words: An Astronomical Unit (AU) is the average distance from the Earth to the Sun.

🎯 Exam Tip: Understand that AU is an average because Earth's orbit around the Sun is slightly elliptical, meaning the distance varies throughout the year.

 

Question 3. Define the light year.
Answer: A light-year is defined as the distance that light travels in a vacuum in one year. This distance is about \( 9.46 \times 10^{15} \text{ m} \). It is used to measure very large distances between stars and galaxies.
In simple words: A light-year is how far light travels in empty space in one whole year.

🎯 Exam Tip: Emphasize that a light-year measures distance, not time, and is used for interstellar scales due to the immense speed of light.

 

Question 4. Convert the temperature from Fahrenheit into Celsius & Kelvin.
Answer: The formulas for converting Fahrenheit to Celsius and Kelvin are as follows:

These formulas help convert a temperature from the Fahrenheit scale to its equivalent values in Celsius and Kelvin scales. Temperature conversion is key in many scientific applications.
In simple words: To change Fahrenheit to Celsius, subtract 32 and divide by 1.8. To change Fahrenheit to Kelvin, first change it to Celsius, then add 273.

🎯 Exam Tip: Remember the key constants: 32 for the freezing point difference and 273.15 (often rounded to 273) for the absolute zero offset between Celsius and Kelvin.

 

Question 5. Convert 100°C into Kelvin.
Answer: To convert a temperature from Celsius to Kelvin, we add 273 to the Celsius value. So, \( 100^\circ\text{C} + 273 = 373 \text{ K} \). Kelvin is an absolute temperature scale, meaning 0 K is absolute zero.
In simple words: To change Celsius to Kelvin, just add 273 to the Celsius number. So, 100 degrees Celsius becomes 373 Kelvin.

🎯 Exam Tip: Always remember that Kelvin is an absolute scale, so there are no degrees (°) in Kelvin measurements, unlike Celsius or Fahrenheit.

 

Question 6. Convert 112°F into K.
Answer: First, convert Fahrenheit to Celsius: \( C = \frac{(112-32)}{1.8} = \frac{80}{1.8} \approx 44.44^\circ\text{C} \). Next, convert Celsius to Kelvin: \( K = 44.44^\circ\text{C} + 273 = 317.44 \text{ K} \). This two-step process is standard for F to K conversion.
In simple words: First, change 112°F to Celsius by subtracting 32 and dividing by 1.8. You get about 44.44°C. Then, add 273 to this to get the Kelvin temperature, which is about 317.44 K.

🎯 Exam Tip: Be careful with decimal calculations and ensure you round appropriately at the final step, usually to two decimal places for temperature conversions unless specified.

 

Question 7. Write the principle of screw gauge.
Answer:

• When a screw is rotated within a nut, the distance its tip moves is directly proportional to the number of rotations made.
• Therefore, the operation of a screw gauge is based on this principle: the linear distance traveled by the screw is directly related to how much it is turned.

This principle allows for very precise measurements of small lengths.
In simple words: A screw gauge works because when you turn the screw, its tip moves forward or backward by a set amount for each turn. The more you turn it, the further it moves.

🎯 Exam Tip: Understanding this principle is crucial for explaining how screw gauges can measure very small thicknesses with high accuracy.

 

Question 8. What are the kinds of units?
Answer: There are primarily two kinds of units used in measurements:

1. Fundamental or basic units
2. Derived units

Fundamental units are independent, while derived units are formed by combining fundamental units. For example, length is fundamental, but area is derived.
In simple words: Units are mainly of two types: fundamental units (like length or mass) and derived units (like area or speed, which come from fundamental units).

🎯 Exam Tip: Be able to identify examples for both fundamental and derived units, as this helps in understanding the building blocks of all measurements.

 

Question 9. Give some examples of fundamental units.
Answer: Examples of fundamental units include:

• Kilogram (kg) for mass
• Metre (m) for length
• Second (s) for time

These units are considered fundamental because they are independent and cannot be expressed in terms of other basic units. There are actually seven fundamental units in the SI system, including Kelvin, Ampere, Candela, and Mole.
In simple words: Some basic units are kilogram for mass, metre for length, and second for time.

🎯 Exam Tip: It is important to know all seven SI fundamental units and their corresponding physical quantities, as they form the basis of all scientific measurements.

 

Question 10. Give some examples of derived units.
Answer: Derived units are formed by multiplying or dividing fundamental units. Some common examples include:

• Area (measured in square metres, \( \text{m}^2 \))
• Volume (measured in cubic metres, \( \text{m}^3 \))
• Density (measured in kilograms per cubic metre, \( \text{kg}/\text{m}^3 \))

These units show how different fundamental quantities interact. Speed (m/s) is another example of a derived unit.
In simple words: Derived units are made by combining basic units. Examples are units for area, volume, and density.

🎯 Exam Tip: When working with derived units, always ensure that the calculation involves the correct combination of fundamental units to get the right derived unit.

 

Question 11. What is the standard unit of weight?
Answer: The standard unit of weight is the Newton (N). Weight is a force, which is the effect of gravity on mass, and forces are measured in Newtons. It's different from mass, which is measured in kilograms.
In simple words: The usual unit for weight is the Newton.

🎯 Exam Tip: Clearly distinguish between mass (amount of matter, measured in kg) and weight (force due to gravity, measured in N).

 

Question 12. What is the standard unit of mass?
Answer: The standard unit of mass in the International System of Units (SI) is the kilogram (kg). It represents the amount of matter in an object. Unlike weight, mass does not change with gravity.
In simple words: The main unit for mass is the kilogram.

🎯 Exam Tip: Remember that the kilogram is the only SI base unit that includes a prefix ("kilo").

 

Question 13. Define Mass.
Answer: Mass is defined as the amount of matter contained within a body. It is a fundamental property of an object that determines its inertia (resistance to change in motion) and its gravitational pull. Mass is a scalar quantity, meaning it only has magnitude.
In simple words: Mass is simply how much stuff or matter an object has inside it.

🎯 Exam Tip: Understand that mass is a constant for a given object, regardless of its location, whereas weight can change depending on gravity.

 

Question 14. Define Weight.
Answer: Weight is defined as the force with which the Earth or any other celestial body attracts an object towards its center. It is a vector quantity, having both magnitude and direction (towards the center of the attracting body). Weight can change depending on the strength of gravity.
In simple words: Weight is the force of gravity pulling an object down towards the Earth's center.

🎯 Exam Tip: The formula for weight is Weight = mass × acceleration due to gravity (W = mg), showing its dependence on both mass and local gravity.

 

Question 15. What is the SI unit of temperature?
Answer: The SI unit of temperature is Kelvin (K). The Kelvin scale is an absolute temperature scale, where 0 K represents absolute zero, the theoretical point at which all atomic motion stops. Unlike Celsius or Fahrenheit, Kelvin does not use the "degree" symbol.
In simple words: The main unit for temperature in science is Kelvin.

🎯 Exam Tip: Always use Kelvin for scientific calculations involving temperature, as it is an absolute scale and simplifies many physical laws.

 

Question 16. What is the measuring unit of the thickness of a plastic carry bag?
Answer: The thickness of a plastic carry bag is typically measured in microns (µm) or micrometers. One micron is equal to \( 10^{-6} \) metres. This unit is used because plastic bags are very thin and require a small unit for accurate measurement.
In simple words: Plastic bags are very thin, so their thickness is measured in microns (µm), which is a very tiny unit.

🎯 Exam Tip: Understand that appropriate units are chosen based on the scale of the measurement - large objects use kilometers, small objects use millimeters, and very thin objects use microns.

VIII. Answer in Detail :

 

Question 1. Write temperature conversion.
Answer: Here's a table showing exact formulas for temperature conversions between Fahrenheit, Celsius, and Kelvin:

These formulas are used to precisely convert a temperature reading from one scale to another. Understanding these conversions is important in science.
In simple words: We use special rules to change temperature readings between Fahrenheit, Celsius, and Kelvin. For example, to get Celsius from Fahrenheit, you subtract 32 and divide by 1.8.

🎯 Exam Tip: Practice applying each conversion formula with different temperature values to ensure you are comfortable with the calculations, especially for converting to and from Kelvin.

 

Question 2. Write about the positive zero error in screw gauge instrument.
Answer: A positive zero error occurs in a screw gauge when, even before any object is placed between its studs and they are brought into contact, the zero mark of the head scale lies below the pitch scale axis. To correct for this, the positive zero error is calculated using the formula \( Z.E = + (n \times LC) \), where 'n' is the head scale coincidence and LC is the least count. For instance, if the 5th division on the head scale lines up with the pitch scale axis, the positive zero error would be \( + (5 \times 0.01 \text{ mm}) = +0.05 \text{ mm} \). The final measurement then requires subtracting this positive zero correction. Ignoring zero error can lead to inaccurate results.
In simple words: A positive zero error happens when the screw gauge reads a small positive value even when it should read zero. This means the zero mark on the circular scale is below the main line. To fix it, you find this extra reading and subtract it from your final measurement.

🎯 Exam Tip: Always check for zero error before making any measurements with a screw gauge; neglecting to do so will lead to consistently incorrect readings.

 

Question 3. Write SI units for the fundamental quantity.
Answer: Here are the SI units for the fundamental quantities:

These seven fundamental quantities and their units form the foundation of the International System of Units. They are all independent of each other and can be used to derive all other physical units.
In simple words: The basic units in science are metre for length, kilogram for mass, second for time, ampere for electric current, kelvin for temperature, mole for amount of substance, and candela for light brightness.

🎯 Exam Tip: It is essential to memorize all seven fundamental quantities and their corresponding SI units, as they are the building blocks for all other measurements in physics and chemistry.

 

Question 4. Convert the following units in metre.
Answer: Here is a conversion of smaller units into metres:

These prefixes (centi, milli, micro, nano, angstrom, fermi) represent various powers of ten, making it easier to express very small lengths in relation to the base unit, the metre. These are commonly used in scientific contexts.
In simple words: We can change small units into metres. For example, 1 centimeter is 0.01 metres, 1 millimeter is 0.001 metres, and even smaller units like micron, nanometre, Angstrom, and Fermi have their own tiny values in metres.

🎯 Exam Tip: Practice converting between these units regularly. It's helpful to remember the power of 10 associated with each prefix (e.g., kilo = \( 10^3 \), milli = \( 10^{-3} \), micro = \( 10^{-6} \)).

 

Question 5. Draw and mark the parts of vernier caliper
Answer: The Vernier caliper is an instrument used for precise measurements of length. Key parts of a Vernier caliper include:

1. Lower fixed jaw
2. Upper fixed jaw
3. Lower movable jaw
4. Vernier scale
5. Retainer
6. Main scale
7. Depth probe

The main scale and Vernier scale work together to provide accurate readings, while the jaws are used to hold the object. The depth probe measures depth. (Image of Vernier caliper diagram showing these parts would typically be included here).
In simple words: A Vernier caliper has different parts like fixed and movable jaws to hold things, a main scale and a Vernier scale for reading measurements, a retainer to hold the movable jaw, and a depth probe to measure how deep something is.

🎯 Exam Tip: Be able to identify and label all the parts of a Vernier caliper and explain the function of each part for practical exams and understanding its operation.

IX. Numerical Problems :

 

Question 1. A piece of iron of volume \( 40 \text{ cm}^3 \) whose density is \( 6.8 \text{ g}/\text{cm}^3 \). Find the mass of iron.
Answer:Given: Density of iron (D) \( = 6.8 \text{ g}/\text{cm}^3 \) Volume of iron (V) \( = 40 \text{ cm}^3 \) We know the formula: Mass (M) \( = \text{Volume} \times \text{Density} \) Substitute the given values: M \( = 40 \text{ cm}^3 \times 6.8 \text{ g}/\text{cm}^3 \) M \( = 272.0 \text{ g} \) So, the mass of the piece of iron is 272.0 grams. This calculation shows how density, volume, and mass are related.
In simple words: To find the mass of the iron, we multiply its volume (\( 40 \text{ cm}^3 \)) by its density (\( 6.8 \text{ g}/\text{cm}^3 \)). This gives us a total mass of 272 grams.

🎯 Exam Tip: Always write down the given values and the formula you are using before performing calculations. Ensure units are consistent (e.g., all in grams and cm³).

 

Question 2. Solve: The mass of 40 apples in a box is 5 kg.
(i) Find the mass of a dozen of them.
(ii) Express the mass of one apple in gram.
Answer:Given: Mass of 40 apples \( = 5 \text{ kg} \) First, convert the total mass to grams, as 1 kg \( = 1000 \text{ g} \). So, mass of 40 apples \( = 5 \times 1000 \text{ g} = 5000 \text{ g} \)
(i) To find the mass of one apple: Mass of 1 apple \( = \frac{5000 \text{ g}}{40} = 125 \text{ g} \) A dozen apples means 12 apples. Mass of a dozen apples \( = 12 \times 125 \text{ g} = 1500 \text{ g} \)
(ii) Express the mass of one apple in gram: Mass of one apple \( = 125 \text{ g} \) These steps demonstrate how to perform calculations for individual items and groups when given total mass.
In simple words: First, change the total weight of 40 apples from 5 kg to 5000 grams. Then, divide 5000 grams by 40 to find that one apple weighs 125 grams. For a dozen (12) apples, multiply 12 by 125 grams to get 1500 grams.

🎯 Exam Tip: Pay close attention to unit conversions (kg to g) and clearly show each step of your calculation, especially for multi-part questions.

X. Answer in Detail :

 

Question 1. How will you find Zero Error of the screw gauge?
Answer: To find the zero error of a screw gauge, you first bring the plane surfaces of the screw and the opposite stud into contact.
**Zero Error:** If the zero of the head scale exactly lines up with the pitch scale axis, then there is no zero error.
**Positive Zero Error:** A positive zero error occurs if the zero of the head scale lies *below* the pitch scale axis when the studs are in contact. For example, if the 5th division on the head scale coincides with the pitch scale axis, the zero error is calculated as \( Z.E = + (n \times LC) \). With a least count (LC) of 0.01 mm, the zero error would be \( + (5 \times 0.01 \text{ mm}) = +0.05 \text{ mm} \). The zero correction is then \( -0.05 \text{ mm} \), which must be subtracted from the observed reading.
**Negative Zero Error:** A negative zero error occurs if the zero of the head scale lies *above* the pitch scale axis. In this case, you count the division on the head scale that coincides with the pitch scale axis, typically counting backward from 100. For instance, if the 95th division coincides, it means the zero is 5 divisions above the axis (100-95=5). The zero error is \( Z.E = - (100 - n) \times LC \). If n = 95, then \( Z.E = - (100 - 95) \times 0.01 \text{ mm} = - (5 \times 0.01 \text{ mm}) = -0.05 \text{ mm} \). The zero correction is then \( +0.05 \text{ mm} \), which must be added to the observed reading. Checking and correcting for zero error is essential to obtain accurate measurements.
In simple words: To find zero error in a screw gauge, close it completely. If the zero line on the circular scale lines up with the main line, there's no error. If the circular scale zero is below the main line, it's a positive error, and you subtract it. If the circular scale zero is above the main line, it's a negative error, and you add it.

🎯 Exam Tip: Accurately identifying and correcting for zero error (positive or negative) is a critical step in using a screw gauge correctly and is often tested in practical examinations.

 

Question 2. How will you find Zero Error of Vernier Caliper? Explain.
Answer: To find the zero error of a Vernier caliper:

• First, carefully unscrew the slider and bring both the jaws into gentle contact with each other.
• Then, check if the zero mark of the main scale aligns perfectly with the zero mark of the Vernier scale.
• If they do not coincide, the instrument has a zero error, which can be either positive or negative.
• **Positive zero error:** This occurs if the zero mark of the Vernier scale is shifted to the right of the main scale's zero. The reading obtained will be more than the actual reading. To correct this, find which Vernier division coincides with any main scale division. For example, if the 5th Vernier division coincides, the positive zero error is \( +5 \times LC \), where LC is the least count (e.g., \( +5 \times 0.01 = +0.05 \text{ cm} \)). This value is subtracted from the final reading.
• **Negative zero error:** This occurs if the zero mark of the Vernier scale is shifted to the left of the main scale's zero. The reading obtained will be less than the actual reading. To correct this, count backward from 10 (or the total number of divisions on the Vernier scale) to find the coinciding line. For example, if the 4th line (when counting backward from 10) coincides, the negative zero error is \( -4 \times LC \) (e.g., \( -4 \times 0.01 = -0.04 \text{ cm} \)). This value is added to the final reading.

Understanding and applying these corrections is vital for precise measurements with a Vernier caliper.
In simple words: To check for zero error in a Vernier caliper, close its jaws tightly. If the main scale's zero and the Vernier scale's zero don't line up, there's an error. If the Vernier zero is to the right, it's a positive error (subtract it). If it's to the left, it's a negative error (add it).

🎯 Exam Tip: Remember that a positive zero error means the instrument over-reads, and a negative zero error means it under-reads, so the correction is always the opposite sign of the error.

 

Question 3. Write short note on the following :
(i) Common balance
(ii) Physical balance Digital balance Spring balance
Answer:**Common (beam) balance:** A common beam balance is used to compare an unknown mass (sample) with known standard reference masses. It works on the principle of moments. Standard masses used typically range from 5g, 10g, 20g, up to 5kg. This type of balance can measure mass accurately, usually up to 5 grams. It is often seen in older shops for weighing goods.
**Physical balance:** A physical balance is more sensitive than a common beam balance and is primarily used in laboratories for more precise mass measurements, often down to a milligram (mg). It also compares an unknown mass with standard reference masses. The reference masses for a physical balance are very small, ranging from 10 mg, 20 mg, 50 mg, all the way up to 200 g. This allows for extremely accurate scientific work.
**Digital balance:** Digital balances are modern electronic devices used for highly accurate mass measurements. They can measure mass precisely, even down to a few milligrams, with some having a least value of 10 mg. They are user-friendly, display readings directly as numbers, and are commonly found in jewelry shops and laboratories due to their ease of use and accuracy.
**Spring balance:** A spring balance is used to measure the weight of an object, not its mass. It consists of a spring fixed at one end and a hook at the other. It operates based on Hooke's Law, which states that the extension of the spring is directly proportional to the force (weight) applied. A pointer moves along a graduated scale, indicating the object's weight. This balance directly measures the gravitational force acting on an object.
In simple words: A **common balance** compares the weight of an object to known weights. A **physical balance** is like a common balance but much more precise, used in labs. A **digital balance** is an electronic scale that shows exact numbers for weight, very easy to use, and very accurate. A **spring balance** measures how heavy an object is by how much it stretches a spring.

🎯 Exam Tip: Be able to differentiate between mass and weight and understand which type of balance measures each. Note the typical accuracy levels for each balance type.

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