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

Textbook Questions and Answers

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.

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:

The balance should carry the stamp of standardisation by the department of weights and measures.
Balance should be stable and the pointer of the balance should be upright.
The underside of the pan should not be tampered with any other weight or layers of other metal.
The weight should be made of metal.

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

Mass	Weight
1. The amount of matter present in a substance is called mass.	1. The gravitational force that acts on this mass is called its weight.
2. It is a scalar quantity.	2. It is a vector quantity.
3. Mass remains same everywhere on the earth.	3. Weight changes from place to place on the ‘ earth.

2. Who is my companion?

Question 1.

Column ‘A’	Column ‘B’
1. Velocity	a. Litre
2. Area	b. Kilogram
3. Volume	c. metre/second
4. Mass	d. kilogram/cubic metre
5. Density	e. square metre

Answer:

Column ‘A’	Column ‘B’
1. Velocity	c. metre/second
2. Area	e. square metre
3. Volume	a. Litre
4. Mass	b. Kilogram
5. Density	d. kilogram/cubic metre

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.

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.

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:

Not using the appropriate device.
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.

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.

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.

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:

Measurement of substances that are precious or of great importance and used in very small quantities is done meticulously and accurately.
Due to advancements in technology, devices that measure very small magnitudes of quantities like distance, mass, time and temperature are available now.
e.g. distance and time in connection with very important sports competitions, mass of gold, body temperature etc.
Devices to be used for this are thermometer, digital balance (Analytical balance) etc.

Project:

Question 1.
Collect information about various physical quantities used in day-to-day life and the devices used for their measurement.

Important Questions and Answers

Fill in the blanks:

Question 1.
The amount of matter present in a substance is called ………………. .
Answer:
mass

Question 2.
…………. is the qualitative measure of the inertia of an object.
Answer:
mass

Question 3.
The larger the mass, the ……………. is the inertia.
Answer:
greater

Question 4.
Mass is a …………… quantity.
Answer:
scalar

Question 5.
…………… does not change from place to place anywhere in the world.
Answer:
mass

Question 6.
The gravitational force that acts on a mass is called its ……………. .
Answer:
weight

Question 7.
Wright is a …………… quantity.
Answer:
vector

Question 8.
System International (SI) is also called ………….. .
Answer:
metric system

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

Question 10.
Gold was weighed in a unit called …………… .
Answer:
gun

Who is my companion?

Question 1.

Column ‘A’	Column ‘B’
1. Gold	a. Hour glass
2. Time	b. Vector
3. Distance	c. Gunj
4. Weight	d. Cubit

Answer

Column ‘A’	Column ‘B’
1. Gold	c. Gunj
2. Time	a. Hour glass
3. Distance	d. Cubit
4. Weight	b. Vector

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

Question 2.
Matter has a natural tendency to resist a change in its state, which is called inertia.
Answer:
True

Question 3.
Weight and mass are both equal quantities.
Answer:
False. Weight and mass are both different quantities

Question 4.
Work is a vector quantity.
Answer:
False. Work is a scalar quantity

Question 5.
Velocity is a scalar quantity.
Answer:
False. Velocity is a vector quantity

Question 6.
Unit of time in both the systems is second.
Answer:
True

Question 7.
Unit of mass in C.G.S. system is kilogram
Answer:
False. Unit of mass in C.G.S. system is gram

Question 8.
Symbol of unit of second is sec.
Answer:
False. Symbol of unit of second is ‘s’

Question 9.
1 cubic foot means 28.317 ml
Answer:
False. 1 cubic foot means 28.317 litres.

Question 10.
Vector quantity requires magnitude only.
Answer:
False. Vector quantity required magnitude and direction both.

Give scientific reasons:

Question 1.
Weight of our body on the moon is less than that on the earth.
Answer:

Gravitational power of moon is less than the earth.
Weight depends on the gravitational power of that place.
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.

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.

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.

Distinguish between the following:

Question 1.
Scalar quantity and Vector quantity
Answer:

Scalar quantity	Vector quantity
1. A quantity that can be completely expressed by its magnitude alone is called a scalar quantity.	1. The quantity that is expressed completely only when magnitude and direction are both given is called a vector quantity.
2. e.g. mass, length, area, breadth, density, time, work etc.	2. e.g. velocity displacement

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

M.K.S. system	C.G.S. system
1. In this system distance is measured in metres, mass in kilograms and time in seconds.	1. In this system distance is measured in centimetres, mass in grams and time in seconds.
2. e.g. Unit of velocity is m/sec, Unit of area is square metre.	2. e.g. Unit of velocity is cm/sec, Unit of area is square centimetre.

Define the following:

Mass: The amount of matter present in a substance is called mass.
Inertia: Matter has a natural tendency to resist a change in its state, which is called Inertia.
Weight: The gravitational force that acts on the mass is called its weight.
Physical Quantities: The quantities in day to day life which can be measured are called physical quantities.
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.

Answer the following questions:

Question 1.
Why would the weight of an object be; maximum at the poles and minimum at the equator?
Answer:

The gravitational force that acts on the mass is called the weight.
The earth is not exactly spherical, it flattens at the poles.
As the distance increases the gravitational force decreases.
Therefore due to reduced distance at the poles compared to the equator, the weight is maximum at the poles than equator.

Question 2.
Why is the weight of an object at a high altitude less than its weight at the sea-level?
Answer:

The gravitational force that acts on the mass is called the weight.
The gravitational force is always inversely proportional to the distance.
So as the distance increases between the earth and the object, the gravitational force decreases.
The gravitational force by which the earth attracts an object towards its centre is called weight.
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.