# Measurements and Experimentation Exe-1A Short Answer Physics Class-9 ICSE Selina Publishers

Measurements and Experimentation Exe-1A System of Unit Short Answer Type for Class-9 ICSE Concise Physics. There is the solutions of short Answer type Questions of your latest textbook which is applicable in 2023-24 academic session. Visit official Website CISCE for detail information about ICSE Board Class-9.

## Measurements and Experimentation Exe-1 A System of Unit Short Answer

(ICSE Class – 9 Physics Concise Selina Publishers)

 Board ICSE Class 9 Subject Physics Writer / Publication Concise selina Publishers Chapter-1 Measurements and Experimentation Exe – 1 A System of Unit Topics Solution of Exe-1(A) Short Answer Type Academic Session 2023-2024

A system of units are the complete set of units, both fundamental and derived, for all kinds of physical quantities.  In the system of units, the first three systems of units (CGS, SI, MKS systems) are the metric systems of units. FPS is not a metric system of units: it is a British system of units.

### Exe-1 A System of Unit Short Answer Type

Ch-1 Measurements and Experimentation Physics Class-9 ICSE Concise

Page 11

#### 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

(i) It should be possible to define the unit without ambiguity.

(ii) The unit should be reproducible.

(iii) The value of units should not change with space and time.

#### Question 2. What are the fundamental units in S.I. system? Name them along with their symbols.

Answer : Fundamental quantities, units and symbols in S.I. system are

 Quantity Unit Symbol Length metre m Mass kilogramme 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 a derived unit with the help of one example

Answer : The units of quantities other than those measured in fundamental units can be obtained in terms of the fundamental units, and thus the units so obtained are called derived units.

Example:

Speed = Distance/time

Hence, the unit of speed = fundamental unit of distance/fundamental unit of time

Or, the unit of speed = metre/second or ms-1.

As the unit of speed is derived from the fundamental units of distance and time, it is a derived unit.

#### Answer : Astronomical unit (A.U.) and kilometer (km) are units of length which are bigger than a metre.

1 km = 1000 m

1 A.U. = 1.496 × 1011 m

#### Answer : Three convenient units of length and their relation with the S.I. unit of length:

(i) 1 Angstrom (Å) = 10-10 m

(ii) 1 kilometre (km) = 103 m

(iii) 1 light year (ly) = 9.46 × 1015 m

#### Answer :  S.I. unit of mass is ‘kilogramme’.

In 1889, one kilogramme was defined as the mass of a cylindrical piece of a platinum-iridium alloy kept at the 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 kilogramme?

The units ‘gramme’ (g) and ‘milligramme’ (mg) are two units of mass smaller than ‘kilogramme’.

1 g = 10-3 kg

1 mg = 10-6 kg

#### Question 8. State two units of mass bigger than a kilogram. Give their relationship with the unit kilogramme.

The units ‘quintal’ and ‘metric tonne’ are two units of mass bigger than ‘kilogramme’.

1 quintal = 100 kg

1 metric tonne = 1000 kg

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

A second is defined as 1/86400th part of a mean solar day, i.e.

1 s = 1/86400 × one mean solar day

#### Answer :  Minute and  hours two units of time bigger than a second

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

—  : End of Measurements and Experimentation Exe-1 A System of Unit Short Answer Type  Solutions :–

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