Maharashtra Board Class 7 Science Chapter 6 Measurement of Physical Quantities Solutions

1. Write Answers To The Following Questions In Your Own Words:

Question a. Why is the weight of the same object different on different planets?
Answer: The weight of the same object is different on different planets because weight depends on the gravitational force of the planet and gravitational force on every planet is different so the weight also differs from planet to planet.
In simple words: An object's weight varies across planets because weight is determined by gravitational force, and each planet has a unique gravitational pull.

🎯 Exam Tip: Focus on understanding the concept of gravitational force and its direct relationship with an object's weight for scoring well.

Question b. What precautions will you take to make accurate measurements in day-to-day affairs?
Answer: Following precautions will be taken to make accurate measurements in day to day affairs:
1. The balance should carry the stamp of standardisation by the department of weights and measures.
2. Balance should be stable and the pointer of the balance should be upright.
3. The underside of the pan should not be tampered with any other weight or layers of other metal.
4. The weight should be made of metal.
In simple words: To ensure accurate measurements, always use standardized, stable, and untampered weighing scales with proper metal weights.

🎯 Exam Tip: Remember these practical tips for precise measurement in daily life, emphasizing standardization and proper device usage.

Question c. What is the difference between mass and weight?
Answer:

In simple words: Mass is the amount of matter in an object and is constant, while weight is the force of gravity on that mass and changes with location.

🎯 Exam Tip: Clearly differentiate between mass (scalar, constant) and weight (vector, variable due to gravity) to earn full marks.

2. Who Is My Companion?

Question 1. Class 7 Science Chapter 6 Measurement Of Physical Quantities Exercise.

Answer:

In simple words: This question matches physical quantities in Column 'A' with their correct units or descriptions in Column 'B'.

🎯 Exam Tip: Carefully learn the S.I. units for various physical quantities to accurately match them in such questions.

3. Explain Giving Examples.

Question a. Scalar quantity:
Answer: A quantity that can be completely expressed by its magnitude alone is called a scalar quantity, e.g. length, breadth, area, mass, temperature, density, time, work. In all these examples a value with a unit is used to express quantities. Thus, we say that the length of a tunnel is 2 km.
In simple words: A scalar quantity is defined solely by its magnitude (size or amount), like length or mass, without needing a direction.

🎯 Exam Tip: Provide clear examples like length or mass to illustrate your understanding of scalar quantities.

Question b. Vector quantity:
Answer: The quantity that is expressed completely only.' v when magnitude and direction are both given is called a vector quantity. Displacement, velocity are vector quantities e.g. a displacement of 20 km towards north, the aeroplane flying at a velocity of 500 km/hr towards Mumbai.
In simple words: A vector quantity requires both magnitude and direction for its complete description, such as displacement or velocity.

🎯 Exam Tip: Always include both magnitude and direction in your examples to correctly define a vector quantity.

4. Explain, Giving Examples, The Errors That Occur While Making Measurements.

Question a. Explain, giving examples, the errors that occur while making measurements.
Answer: Major causes of errors in measurement are:
1. Not using the appropriate device.
2. Not using the device properly.
Example: While buying things at grocery shops and the vegetable market remember to look out for the following:
• The balance should carry the stamp of standardisation by the department of weights and measures.
• Balance should be stable. The pointer of the balance should be upright.
• No changes should be done on the underside of the pan of the balance.
• Weight should be made up of metals and it has to be standardized.
In simple words: Measurement errors arise from using incorrect devices or improper technique, like not checking for standardized or tampered weighing scales.

🎯 Exam Tip: Focus on identifying both the general causes and specific examples of measurement errors, especially practical ones like checking a balance's standardization.

5. Give Reasons:

Question a. It is not proper to measure quantities by using body parts as units.
Answer: It is not proper to measure quantities by using body parts as units because length of the body parts changes from person to person, so accurate measurement can not be found with the body parts as units.
In simple words: Measuring with body parts is inaccurate because their sizes vary among individuals, leading to inconsistent measurements.

🎯 Exam Tip: Emphasize the lack of uniformity in body part measurements as the key reason for their unsuitability as standard units.

Question b. It is necessary to get the weights and measures standardized at regular intervals.
Answer: It is necessary to get the weights and measures standardized at regular intervals because of that accurate weight and measurement can be taken. Errors will be avoided.
In simple words: Regular standardization of weights and measures is crucial to ensure accuracy and prevent errors in measurements over time.

🎯 Exam Tip: Highlight accuracy and error prevention as the primary benefits of periodic standardization of measuring instruments.

6. Explain The Need For Accurate Measurement And The Devices To Be Used For That.

Question a. Explain the need for accurate measurement and the devices to be used for that.
Answer:
1. Measurement of substances that are precious or of great importance and used in very small quantities is done meticulously and accurately.
2. Due to advancements in technology, devices that measure very small magnitudes of quantities like distance, mass, time and temperature are available now.
3. e.g. distance and time in connection with very important sports competitions, mass of gold, body temperature etc.
4. Devices to be used for this are thermometer, digital balance (Analytical balance) etc.
In simple words: Accurate measurement is vital for precious items and technological precision, using advanced tools like thermometers and digital balances for precise readings.

🎯 Exam Tip: Illustrate the need for accuracy with examples of high-value or critical measurements, linking them to specific, appropriate measuring devices.

Fill In The Blanks:

Question 1. Std 7 Science Chapter 6 Measurement Of Physical Quantities. The amount of matter present in a substance is called ..........
Answer: mass
In simple words: The total amount of material an object contains is known as its mass.

🎯 Exam Tip: Remember that mass refers to the quantity of matter in an object.

Question 2. Measurement Of Physical Quantities Class 7 Exercise. .......... is the qualitative measure of the inertia of an object.
Answer: mass
In simple words: Mass is the fundamental property that indicates how much an object resists changes to its state of motion or rest.

🎯 Exam Tip: Connect mass directly to inertia, recognizing it as the measure of an object's resistance to change in motion.

Question 3. 6. Measurement Of Physical Quantities. The larger the mass, the .......... is the inertia.
Answer: greater
In simple words: Objects with more mass exhibit a stronger tendency to resist changes in their motion.

🎯 Exam Tip: Understand the direct proportionality between mass and inertia; more mass means more inertia.

Question 4. 6.Measurement Of Physical Quantities. Mass is a .............quantity.
Answer: scalar
In simple words: Mass is a scalar quantity, meaning it is described only by its magnitude, not direction.

🎯 Exam Tip: Recall that scalar quantities, like mass, have only magnitude and no direction.

Question 5. Physical Quantities And Measurement Class 7. .......... does not change from place to place anywhere in the world.
Answer: mass
In simple words: Mass is an intrinsic property of an object that remains constant regardless of its location.

🎯 Exam Tip: Recognize mass as a constant quantity that is unaffected by gravitational changes or location.

Question 6. Measurement Of Physical Quantities Class 7. The gravitational force that acts on a mass is called its ..........
Answer: weight
In simple words: The force exerted on an object due to gravity is defined as its weight.

🎯 Exam Tip: Differentiate mass from weight by remembering that weight is the force of gravity on mass.

Question 7. 6 Measurement Of Physical Quantities. Wright is a ............... quantity.
Answer: vector
In simple words: Weight is a vector quantity, possessing both magnitude (how heavy) and direction (towards the center of gravity).

🎯 Exam Tip: Understand that weight is a force, and forces are always vector quantities, having both magnitude and direction.

Question 8. System International (SI) is also called ..........
Answer: metric system
In simple words: The International System of Units (SI) is also commonly known as the metric system.

🎯 Exam Tip: Remember that SI system is synonymous with the metric system, essential for standardized measurements.

Question 9. In Egypt in ancient times, the distance from a man's elbow to the tip of his middle finger was called a ..............
Answer: cubit
In simple words: An ancient unit of length, the cubit, was based on the measurement from the elbow to the middle fingertip.

🎯 Exam Tip: Be familiar with historical units of measurement like the cubit, as they demonstrate early attempts at standardization.

Question 10. Gold was weighed in a unit called ..........
Answer: gun
In simple words: In some historical contexts, gold was weighed using a unit known as 'gun' (as per the provided text).

🎯 Exam Tip: Note the specific historical units used for precious metals like gold to understand diverse measurement practices.

Who Is My Companion?

Question 1.

Answer:

In simple words: This matching question connects various items in Column 'A' with their relevant characteristics or historical units from Column 'B'.

🎯 Exam Tip: Practice associating physical concepts with their historical or scientific contexts to master matching questions.

Say Whether True Or False. Correct And Rewrite The False Statements:

Question 1. The standards of the six fundamental units are kept in the National Physical Laboratory at New Delhi.
Answer: True
In simple words: The official standards for the six fundamental units are indeed maintained at the National Physical Laboratory in New Delhi.

🎯 Exam Tip: Know the location where official measurement standards are preserved for general knowledge and exam accuracy.

Question 2. Matter has a natural tendency to resist a change in its state, which is called inertia.
Answer: True
In simple words: Inertia is the inherent property of matter that causes it to resist any alteration to its current state of rest or motion.

🎯 Exam Tip: Clearly define inertia as the property of matter resisting changes in its state of motion or rest.

Question 3. Weight and mass are both equal quantities.
Answer: False. Weight and mass are both different quantities
In simple words: Weight and mass are distinct physical quantities; mass is the amount of matter, while weight is the gravitational force on that mass.

🎯 Exam Tip: Emphasize that mass is a measure of matter, while weight is a force, thus making them different quantities.

Question 4. Work is a vector quantity.
Answer: False. Work is a scalar quantity
In simple words: Work is a scalar quantity because it is defined by its magnitude (energy transferred) without a specific direction.

🎯 Exam Tip: Remember that work, being a form of energy transfer, is a scalar quantity, not a vector.

Question 5. Velocity is a scalar quantity.
Answer: False. Velocity is a vector quantity
In simple words: Velocity is a vector quantity because it describes both the speed and direction of an object's motion.

🎯 Exam Tip: Clearly state that velocity is a vector quantity, always comprising both magnitude (speed) and direction.

Question 6. Unit of time in both the systems is second.
Answer: True
In simple words: The second is universally adopted as the standard unit for time measurement across both MKS and CGS systems.

🎯 Exam Tip: Recognize 'second' as the consistent unit for time in both the CGS and MKS systems for accuracy.

Question 7. Unit of mass in C.G.S. system is kilogram
Answer: False. Unit of mass in C.G.S. system is gram
In simple words: In the CGS system, the unit for mass is gram, whereas kilogram is the unit in the MKS/SI system.

🎯 Exam Tip: Distinguish between the CGS system's unit for mass (gram) and the MKS system's unit (kilogram).

Question 8. Symbol of unit of second is sec.
Answer: False. Symbol of unit of second is 's'
In simple words: The correct and standardized symbol for the unit of second is 's', not 'sec'.

🎯 Exam Tip: Use the standard 's' as the symbol for seconds to ensure scientific correctness.

Question 9. 1 cubic foot means 28.317 ml
Answer: False. 1 cubic foot means 28.317 litres.
In simple words: One cubic foot is equivalent to 28.317 litres, not milliliters, indicating a much larger volume.

🎯 Exam Tip: Be precise with unit conversions; a cubic foot is equivalent to litres, not milliliters.

Question 10. Vector quantity requires magnitude only.
Answer: False. Vector quantity required magnitude and direction both.
In simple words: A vector quantity is fully defined only when both its magnitude (size) and its direction are specified.

🎯 Exam Tip: Always remember that vector quantities are characterized by both magnitude and a specific direction.

Give Scientific Reasons:

Question 1. Weight of our body on the moon is less than that on the earth.
Answer:
1. Gravitational power of moon is less than the earth.
2. Weight depends on the gravitational power of that place.
3. Since the gravitational power of the moon is less than that of the earth, the weight on moon is less than that on the earth.
In simple words: Your body weighs less on the Moon because the Moon's gravitational pull is weaker than Earth's, and weight is a direct measure of gravitational force.

🎯 Exam Tip: Explain the direct relationship between weight and gravitational force, using the Moon's weaker gravity as a prime example.

Question 2. Mass is a scalar quantity
Answer: Mass is a scalar quantity because it can be completely expressed by its magnitude alone, so it is scalar quantity.
In simple words: Mass is a scalar quantity because it is fully described by its numerical value (magnitude) without needing any directional information.

🎯 Exam Tip: Define scalar quantity and then apply it to mass, stating that only magnitude is needed for its complete description.

Question 3. Weight is a vector quantity.
Answer: Weight can be expressed completely only when magnitude and direction are both given so weight is a vector quantity.
In simple words: Weight is a vector quantity because it has both a magnitude (how heavy an object is) and a direction (downwards, towards the center of gravity).

🎯 Exam Tip: Emphasize that weight is a force, and forces are always vectors, requiring both magnitude and direction.

Distinguish Between The Following:

Question 1. Scalar quantity and Vector quantity
Answer:

In simple words: Scalar quantities only have magnitude, like mass or time, while vector quantities have both magnitude and direction, such as velocity or displacement.

🎯 Exam Tip: Clearly state the defining characteristic (magnitude vs. magnitude + direction) and provide distinct examples for each to earn full marks.

Question 2. M.K.S. system and C.G.S. system
Answer:

In simple words: The MKS system uses meters, kilograms, and seconds, while the CGS system uses centimeters, grams, and seconds as its fundamental units.

🎯 Exam Tip: Remember the base units for length, mass, and time for both MKS (meter, kilogram, second) and CGS (centimeter, gram, second) systems.

Define The Following:

1. Mass: The amount of matter present in a substance is called mass.

2. Inertia: Matter has a natural tendency to resist a change in its state, which is called Inertia.

3. Weight: The gravitational force that acts on the mass is called its weight.

4. Physical Quantities: The quantities in day to day life which can be measured are called physical quantities.

5. Standardization: The process of checking things against a standard measure from time to time is called standardization.

Write Answers To The Following Questions In Your Own Words.

Question 1. What is an atomic clock?
Answer: An extremely accurate type of clock which is regulated by the vibrations of an atomic or molecular system such as caesium atom or ammonia is called atomic clock. It is used to maintain standard times of countries accurately.
In simple words: An atomic clock is a highly precise timekeeping device that uses the natural oscillations of atoms to maintain extremely accurate time standards.

🎯 Exam Tip: Highlight the precision and the use of atomic vibrations (e.g., caesium) as key features when defining an atomic clock.

Answer The Following Questions:

Question 1. Why would the weight of an object be; maximum at the poles and minimum at the equator?
Answer:
1. The gravitational force that acts on the mass is called the weight.
2. The earth is not exactly spherical, it flattens at the poles.
3. As the distance increases the gravitational force decreases.
4. Therefore due to reduced distance at the poles compared to the equator, the weight is maximum at the poles than equator.
In simple words: An object's weight is highest at the poles and lowest at the equator because Earth is flattened at the poles, meaning you are closer to the center of gravity there, resulting in a stronger gravitational pull.

🎯 Exam Tip: Explain that Earth's oblate spheroid shape causes varying distances from its center, directly impacting gravitational force and thus weight at different latitudes.

Question 2. Why is the weight of an object at a high altitude less than its weight at the sea-level?
Answer:
1. The gravitational force that acts on the mass is called the weight.
2. The gravitational force is always inversely proportional to the distance.
3. So as the distance increases between the earth and the object, the gravitational force decreases.
4. The gravitational force by which the earth attracts an object towards its centre is called weight.
5. The weight at the sea-level is higher than at higher altitude, as the object is at a greater distance at higher altitudes compared to sea-level.
In simple words: Weight decreases with altitude because the gravitational force weakens as an object moves farther away from the Earth's center.

🎯 Exam Tip: Explain the inverse relationship between gravitational force and distance from Earth's center to clarify why weight decreases with increasing altitude.