ICSE Physics Class-9 chapter -1 Measurements and Experiments, Solution Ex-1A

Exercise 1(A) — Multiple Choice Type

Question 1

The condition(s) essential for a unit to be accepted internationally :

1. The unit should be of convenient size and without any ambiguity.
2. The unit should be reproducible.
3. The value of the unit should not change with space and time.
4. All of the above.

Answer

All of the above

Question 2

In mechanics, the three fundamental quantities are:

1. Length, mass, velocity
2. Mass, time, density
3. Mass, time, pressure
4. Length, mass, time

Answer

Length, mass, time

How many units are fundamental and complementary?

1. 2 fundamental, 7 complementary
2. 3 fundamental, 6 complementary
3. 7 fundamental, 2 complementary
4. 4 fundamental, 5 complementary

Answer

7 fundamental, 2 complementary

Question 4

The fundamental unit is —

1. newton
2. pascal
3. hertz
4. second

Answer

second

Question 5

Which of the following unit is not a fundamental unit:

1. metre
2. litre
3. second
4. Kilogram

Answer

Litre

Reason — Metre, second and kilogram are the fundamental units whereas litre is a derived unit.

Question 6

One millimeter is ............... part of a metre:

1. One hundredth
2. One thousandth
3. One billionth
4. One millionth

Answer

One thousandth

Question 7

One astronomical unit is equal to:

1. 1.496 x 10¹¹ metre
2. 1.596 x 10¹² metre
3. 1.498 x 10¹⁰ metre
4. 1.398 x 10¹¹ metre

Answer

1.496 x 10¹¹ metre

Question 8

The distance of stars from earth is generally measured in:

1. Kilometre
2. Light year
3. Angstrom
4. Fermi

Answer

Light year

Question 9

1 Fermi is equal to:

1. 10^-14 m
2. 10^-10 m
3. 10¹⁵ m
4. 10^-15 m

Answer

10^-15 m

Question 10

The unit of time is:

1. light year
2. parsec
3. leap year
4. angstrom

Answer

leap year

Question 11

1 Å is equal to:

1. 0.1 nm
2. 10^-10cm
3. 10^-8m
4. 10⁴µ

Answer

0.1 nm

One metric tonne is equal to :

1. 10 quintal
2. 100 quintal
3. 1000 quintal
4. 25 quintal

Answer

10 quintal

Question 13

Light-year is the unit of:

1. Time
2. Length
3. Mass
4. none of these

Answer

Length

Question 14

One solar mass is equal to :

1. 3 x 10²⁰ kg
2. 2 x 10²⁷ kg
3. 2 x 10³⁰ kg
4. 3 x 10³⁰ kg

Answer

2 x 10³⁰ kg

Question 15

One lunar cycle is nearly equal to:

1. 28.5 days
2. 29.5 days
3. 30 days
4. 30.5 days

Answer

29.5 days

Question 16

One shake is equal to:

1. 10^-9 s
2. 10^-8 s
3. 10^-10 s
4. 10⁸ s

Answer

10^-8 s

Question 17

Which of the following unit is equivalent to watt?

1. volt x ampere
2. volt/ampere
3. ampere/volt
4. Ohm

Answer

volt x ampere

Question 18

Which one of the following is a derived unit?

1. metre
2. kelvin
3. metre³
4. mole

Answer

metre³

Question 19

The S.I. unit of energy is:

1. joule
2. Kg m²
3. Kg m²s^-3
4. Kg m²s^-1

Answer

joule

Question 20

The S.I. unit of pressure is:

1. Kg m^-2s^-2
2. Kg m^-1s^-2
3. Kg m²
4. Kg ms^-2

Answer

Kg m^-1s^-2

Question 21

Which of the following is the smallest unit?

1. millimetre
2. Angstrom
3. Fermi
4. metre

Answer

Fermi

Reason — Fermi is 10^-15th part of a metre. i.e., 1 fermi = 10^-15 m, hence it is the smallest unit.

Angstrom = 10^-10th part of a metre.
Millimetre = 10^-3th part of a metre.

Exercise 1(A) — Very Short Answer Type

Question 1

What is meant by measurement?

Answer

Measurement is the process of comparison of the given quantity with the known standard quantity of the same nature.

Question 2

What do you understand by the term unit?

Answer

Unit is the quantity of a constant magnitude which is used to measure the magnitudes of other quantities of the same nature.

Question 3

How is a physical quantity expressed?

Answer

A physical quantity is expressed in terms of the following parameters:

1. The unit in which the quantity is being measured, and
2. The numerical value which expresses, how many times the above selected unit is contained in the given quantity.

Thus, the magnitude of physical quantity is expressed as : Physical quantity = (numerical value) x (unit)

Question 4

Name the three fundamental quantities.

Answer

The three fundamental quantities are —

1. Mass
2. Length
3. Time

Question 5

What is the S.I. unit of Luminous intensity?

Answer

The S.I. unit of Luminous intensity is candela (cd).

Question 6

Define one parsec.

Answer

One parsec is the distance from where the semi major axis of orbit of earth (1 A.U.) subtends an angle of one second.

Question 7

Define a fundamental unit.

Answer

A fundamental unit is that which is independent of any other unit or which can neither be changed nor can be related to any other fundamental unit.

Example – Units of mass, length, time, temperature, current etc.

Question 8

Define a derived unit.

Answer

Derived units are those which depend on the fundamental units or which can be expressed in terms of fundamental units.

Example: For the measurement of area, we need to measure length and breadth in the unit of length and then express area in a unit which is length x length or (length)²

Question 9

Define standard metre.

Answer

The standard metre is defined in terms of speed of light, according to which, one metre is the distance travelled by light in 1/299,792,458 of a second in air (or vacuum).

Question 10

How is nanometer related to Angstrom ?

Answer

Relation between nanometer (nm) and Angstrom (Å) is expressed as:
    1 nanometer = 10 Å

Question 11

Complete the following —

1. 1 light year = ________ m
2. 1 m = ________ Å
3. 1 m = ________ µ
4. 1 micron = ________ Å
5. 1 fermi = ________ m

Answer

1. 1 light year = 9.46 x 10¹⁵ m
2. 1 m = 10¹⁰ Å
3. 1 m = 10⁶ µ
4. 1 micron = 10⁴ Å
5. 1 fermi = 10^-15 m

Question 12

Complete the following —

1. 1g = ______kg
2. 1mg = ________kg
3. 1 quintal = ________kg
4. 1 a.m.u (or u) = ________kg

Answer

1. 1 g = 10^-3 kg
2. 1 mg = 10^-6 kg
3. 1 quintal = 100 kg
4. 1 a.m.u (or u) = 1.66 x 10^-27 kg

Question 13

What is a leap year?

Answer

A leap year is the year in which the month of February is of 29 days.

1 Leap year = 366 days

Every fourth year (i.e., the year divisible by 4) has one day extra in the month of february (i.e., February has 29 days) and so it is the leap year.

Question 14

'The year 2024 will have February of 29 days'. Is this statement true?

Answer

Yes the statement is true.

We know that, if any year is divisible by 4, then it is a leap year and in a leap year, February has 29 days. As, the year 2024 is divisible by 4, so it will have 29 days in February.

Question 15

What is a lunar month?

Answer

A lunar month is the time of one lunar cycle, i.e., it is the amount of time it takes for the Moon to complete one orbit around the Earth and it is nearly equal to 29.5 days.

Question 16

Complete the following —

1. 1 nano second = ________s
2. 1 µs = _______s
3. 1 mean solar day = ________s
4. 1 year = ________s

Answer

1. 1 nano second = 10^-9 s
2. 1 µs = 10^-6 s
3. 1 mean solar day = 86400 s
4. 1 year = 3.15 x 10⁷ s

Question 17

Name the physical quantities which are measured in the following units —

1. u
2. ly
3. ns
4. nm

Answer

Physical quantity related to the unit are as follows —

  

Unit	Physical quantity
u	Mass
ly	Distance
ns	Time
nm	Length

Question 18

Write the derived units of the following —

1. Speed
2. Force
3. Work
4. Pressure

Answer

The derived units of the following quantities are as follows —

Quanity	Derived unit
Speed	m/s
Force	kg m /s²
Work	kg m²/s²
Pressure	kg/ ms²

Question 19

How are the following derived units related to the fundamental units?

1. newton
2. watt
3. joule
4. pascal

Answer

Derived unit	Fundamental unit
newton	kg m /s²
watt	kg m2/s³
joule	kg m²/s²
pascal	kg /m¹s²

Question 20

Name the physical quantities related to the following units —

1. km²
2. newton
3. joule
4. pascal
5. watt

Answer

The physical quantities related to the following units are —

Unit	Physical quantity
km2	area
newton	force
joule	energy
pascal	pressure
watt	power

Exercise 1(A) — Short Answer Type

Question 1

What are the three requirements for selecting a unit of a physical quantity?

Answer

The three requirements for selecting a unit of a physical quantity are —

1. The unit should be of convenient size.
2. It should be possible to define the unit without any ambiguity.
3. The unit should be reproducible.
4. The value of unit should not change with space and time. (i.e. it must always remain same everywhere).

Question 2

What are the fundamental units in S.I. system? Name them along with their symbols.

Answer

The fundamental units in S.I. system along with their symbols are as follows —

Quantity	Unit	Symbol
Length	metre	m
Mass	kilogram	kg
Time	second	s
Temperature	kelvin	K
Luminous intensity	candela	cd
Electric current	ampere	A
Amount of substance	mole	mol
Angle	radian	rd
Solid angle	steradian	st-rd

Question 3

Explain the meaning of derived unit with the help of one example.

Answer

The units of quantities other than those measured in fundamental units, can be expressed in terms of the fundamental units and they are called derived units.

Thus, derived units are those which depend on the fundamental units or which can be expressed in terms of the fundamental units.

Example – For the measurement of area, we need to measure length and breadth in the unit of length and then express area in a unit which is:

length x length or (length)².

Question 4

Name two units of length which are bigger than a metre. How are they related to the metre?

Answer

The units of length which are bigger than a metre are —

1. Astronomical Unit (A.U.) — One astronomical unit is equal to the mean distance between the earth and the sun. Relation between metre and astronomical unit is expressed as:
       A.U. = 1.496 x 10¹¹m
2. Light year (ly) — A light year is the distance travelled by light in vacuum, in one year. Relation between metre and light year is expressed as:
       1 light year = 9.46 x 10¹⁵m

Question 5

Name the three convenient units used to measure length ranging from very short to very long value. How are they related to the S.I. unit ?

Answer

The 3 convenient units used to measure length ranging from very short to very long value are —

1. centimetre (cm)
2. metre (m)
3. kilometer (km)

S.I. unit of length is meter (m). Relation between meter (m) and centimetre is —

    1 m = 100 cm

Relation between metre (m) and kilometre is —

    1 km = 1000 m

Question 6

Name the S.I. unit of mass and define it.

Answer

The S.I. unit of mass is kilogram (Kg).

One kilogram is defined as the mass of a cylindrical piece of platinum-iridium alloy kept at International Bureau of Weights and Measures at Serves near Paris.

Question 7

State two units of mass smaller than a kilogram. How are they related to kilogram ?

Answer

The two units of mass smaller than a kilogram (kg) are:

1. gram (g) — Relation between gram and kilogram is:
       1 g = 10^-3 kg
2. milligram (mg) — Relation between miligram and kilogram is:
       1 mg = 10^-6 kg

Question 8

State two units of mass bigger than a kilogram. Give their relationship with the kilogram.

Answer

The two units of mass bigger than a kilogram (kg) are:

1. quintal — It is one hundred times a kilogram. Relation between quintal and kilogram is:
       1 quintal = 100 kg
2. metric tonne — It is one thousand times a kilogram. Relation between metric tonne and kilogram is:
       1 metric tonne = 1000 kg

Question 9

Name the S.I. unit of time and define it.

Answer

The S.I. unit of time is second (s).

A second can be defined as 1/86400th part of a mean solar day.

Question 10

Name two units of time bigger than a second. How are they related to second?

Answer

The two units of time bigger than a second (s) are:

1. minute (min) — One minute is the duration of 60 seconds. Relation between minute and second is:
       1 min = 60s
2. hour (h) — One hour is the duration of 60m minutes. Relation between hour and second is:
       1 h = 3600s

Exercise 1(A) — Numericals

Question 1

The wavelength of light of a particular colour is 5800 Å.

Express it in —

(a) nanometer and

(b) metre

Answer

As we know, 1nm = 10 Å

Given,

The wavelength of light = 5800 Å

Substituting the value of wavelength in the relation 

  10 Å = 1nm

1Å = 0.1nm

5800 Å = 5800 x 0.1nm

Hence, wavelength of 5800 Å in nm = 580 nm.

(b) As we know,
1m = 10¹⁰ Å

Given,

The wavelength of light = 5800 Å

Substituting the value of wavelength in the relation above, we get,

1m = 10¹⁰ Å

 10¹⁰ Å = 1 m

 1 Å = 1 x 10 ^-10 m

5800 Å = 5800 x 10 ^-10 m

Hence, wavelength of 5800 Å in m = 5.8 x 10 ^-7m.

Question 2

The size of a bacteria is 1 µ. Find the number of bacteria in 1m length.

Answer

Given,

Size of a bacteria = 1 µ

Total length = 1m

​

As we know, 1 µ = 10^-6m, substituting the value in the relation above we get:

Number of bacteria in 1m length = 10⁶ µ

Hence,
number of bacteria in 1m length = 10⁶ bacteria.

Question 3

The distance of a galaxy from the earth is 5.6 x 10²⁵m. Assuming the speed of light to be 3 x 10⁸ m/s . Find the time taken by light to travel this distance.

​

Answer

Given,

Time taken=distance/ speed​

distance = 5.6 x 10²⁵m

speed = 3 x 10⁸ m/s

Substituting the values in the formula above we get,

Time taken= 5.6 x 10²⁵m ÷ 3 x 10⁸ m/s

∴, time taken by light = 1.87 x 10¹⁷s.

Question 4

The wavelength of light is 589nm. What is its wavelength in Å?

Answer

As we know, 1nm = 10 Å

Given,

The wavelength of light = 589nm

Substituting the value of wavelength in the relation above, we get,

1nm = 10 Å

589 nm =589 x 10 Å

Hence, the wavelength of light in Å is 5890 Å.

Question 5

The distance of the nearest star, Proxima Centauri, from the Earth is 4.0 x 10¹³ km. Express it in light year.

Answer

1 Light year = 9.46 x 10¹² km

or 9.46 x 10¹² km = 1light year

 1 km = (1  ÷ 9.46 x 10¹²) light year

 4.0 x 10¹³  km =( 4.0 x 10¹³   ÷ 9.46 x 10¹²) light year

= 4.2 light years.

Hence, distance of the nearest star from earth = 4.2 light years.

Question 6

It takes time 8 min for light to reach from the sun to the earth surface. If speed of light is taken to be 3 x 10⁸m/s, find the distance from the sun to the earth in km.

Answer

As we know, Distance = speed x time

Given,

Speed = 3 x 10⁸m/s

Time = 8 min = 8 x 60s = 480s

Substituting the values in the formula above we get,

Distance = 3 x 10⁸ x 480 = 1440 x 10⁸ m.

Converting the distance to km:

Distance = 1.44 x 10⁸ km

∴,
the distance from the sun to the earth is 1.44 x 10⁸ km.

Question 7

'The distance of a star from the earth is 8.33 light minutes'. What do you mean by this statement? Express the distance in metre.

Answer

'The distance of a star from the earth is 8.33 light minutes' implies, it takes 8.33 minutes for light to reach the earth from the star.

As we know,
Distance = speed x time

Given,

Speed = 3 x 10⁸ms^-1

Time = 8.33 min
= 8.33 x 60s
= 499.8s
≈ 500s

Substituting the values in the formula above we get,

Distance = 3 x 10⁸ x 500
= 1500 x 10⁸
= 1.5 x 10¹¹

∴, the distance from the star to the earth is 1.5 x 10¹¹ m.

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