Tag: measurements and units

Questions Related to measurements and units

Consider the following two statements A and B and identify the correct answer.
A) The size ($u$) of the unit of physical quantity and its numerical magnitude ($n$) are related to each other by the relation nu $=$ constant
B) The choice of mass, length and time as fundamental quantities is not unique.

physics measurements and units summary of si units fundamental quantities system of units

  1. A is true but B is false

  2. B is true but A is false

  3. Both A and B are true

  4. Both A and B are false

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Correct Option: C
Explanation:

A: eg. $10$ seconds, where $n=10, u=$seconds. This is constant.
B: We can choose any quantity as fundamental and derive other quantities with respect to that

Which of the following is / are not unit(s) of time ?
a) Parsec                   b) Light-year 

c) Micron                  d) Second

physics measurements and units summary of si units fundamental quantities system of units

  1. a and c

  2. a and b

  3. a, b and c

  4. all a, b, c and d

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Correct Option: C
Explanation:

Parsec, light year and micron are all units of length. 

Only second is the unit of time.

Debye is a unit of

physics measurements and units summary of si units fundamental quantities system of units

  1. rms velocity

  2. force

  3. specific gravity

  4. electric dipole moment

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Correct Option: D
Explanation:

The correct option is D.

The Debye, represented as D, is a CGS unit of electric dipole moment. This name was given in the honor of the physicist Peter J. W. Debye. Its value is defined as $1 \times { 10 } ^{ -18 }$ statcoulomb-centimetre.

The SI unit of luminous intensity is

physics measurements and units summary of si units fundamental quantities system of units

  1. Ampere

  2. Candela

  3. Mole

  4. None of these

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Correct Option: B
Explanation:

The SI unit of luminous intensity is Candela

The amount of substance in the SI system of units is represented by 

physics measurements and units summary of si units fundamental quantities system of units

  1. Candela

  2. Mole

  3. Weight

  4. Kilogram

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Correct Option: B
Explanation:

Mole represents the amount of substance in the SI system of units.

The SI unit of temperature is

physics measurements and units summary of si units fundamental quantities system of units

  1. Kelvin

  2. Second

  3. Mole

  4. Candela

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Correct Option: A
Explanation:

SI unit of temperature is Kelvin denoted by  $K$.

$\displaystyle N{ kg }^{ -1 }$ is the unit of 

physics measurements and units summary of si units fundamental quantities system of units

  1. Retardation

  2. Acceleration

  3. Rate of change of velocity

  4. All of these

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Correct Option: D
Explanation:
Acceleration is measured as   $a = \dfrac{Force}{mass}$

Thus, $N kg^{-1}$ is the unit of acceleration.

Retardation is the acceleration in the opposite direction.

Also, acceleration is defined as rate of change of velocity of the body.
Thus option D is correct.

Unit for the rate of change of velocity is 

physics measurements and units summary of si units fundamental quantities system of units

  1. $\displaystyle m/s$

  2. $\displaystyle { m }/{ { s }^{ 2 } }$

  3. $\displaystyle Ns$

  4. $\displaystyle N/s$

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Correct Option: B
Explanation:
Rate of change of velocity is known as acceleration.
Unit of acceleration is  $m/s^2$

Kilowatt hour $\left(kWh\right)$ represents the unit of

physics measurements and units summary of si units fundamental quantities system of units

  1. Power

  2. Impulse

  3. Momentum

  4. Energy

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Correct Option: D
Explanation:
Kilowatt hour $(kWh)$ is the unit of energy.
$1 \ kWh = 3.6\times 10^6 \ J$

Which of the following physical quantities has no unit?

physics measurements and units summary of si units fundamental quantities system of units

  1. Relative density

  2. Density

  3. Pressure

  4. Thrust

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Correct Option: A
Explanation:
Relative density is defined as the ratio of density of a given substance to the density of water.
Thus relative density has no unit.