Tag: measurements and units

Questions Related to measurements and units

Light year is a measurement of 

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

  1. Speed of aeroplanes

  2. Speed of light

  3. Stellar distances

  4. Speed of rockets

Show answer
Correct Option: C
Explanation:

Light year is the unit of astronomical distance. It is a distance that light travels in one year. 

So, $1$ light year $=(3\times 10^8)\times (365\times 24\times 3600)=9.46\times 10^{15} m$

Write S.I. unit of charge

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

  1. C

  2. A

  3. N m$^2$

  4. None of the above

Show answer
Correct Option: A
Explanation:

SI unit of charge is Coulomb which is represented by the symbol $C$.

The quantity represented by the product of "Resistance and inductance" is

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

  1. mass

  2. length

  3. time

  4. none

Show answer
Correct Option: D
Explanation:

The product of resistance and inductance is not represented by any quantity given above.

SI unit of moment of couple is ____.

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

  1. $N m$

  2. $dyne \ cm$


  3. $N m^{-2}$

  4. none of the above

Show answer
Correct Option: A
Explanation:
Moment of couple is torque which is equal to the product of force applied to the distance.
Moment of couple   $\tau = rF$
SI unit of moment of couple is $Nm$

The dimensions of ratio of magnetic flux $(\phi)$ and permeability $(u)$ are:

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

  1. $[M^0 L^1 A^1 T^0]$

  2. $[M^0 L^{-3} T^0 A^1]$

  3. $[M^0 L^{-1} T^1 A^{-1}]$

  4. $[M^0 L^2 T^0 A^1]$

Show answer
Correct Option: A
Explanation:

Magnetic flux $= B.A.$
Permatibility $= \dfrac{B}{H} = \dfrac{J}{A.M}$

$= \dfrac{BA}{B/H}$

$= \dfrac{BAH}{B} = AH$

$= [L^2] [AC^{-1}]$

$= [M^o LAT^o]$

The solid angle subtended at any point inside the surface due to small area ds is given by 

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

  1. $r^2ds \cos \theta$

  2. $\dfrac{ds \cos \theta }{r^2}$

  3. $\dfrac{ds\cos \theta }{r}$

  4. $\dfrac{r^2}{ds \cos \theta}$

Show answer
Correct Option: B
Explanation:

The solid angle $\Omega=\dfrac{A}{r^2}$

where, $A=$ area
When solid angle subtended at any point inside the surface due to small area $ds$
$A=ds$ $cos\theta$
Solid angle $\Omega=\dfrac{dscos\theta}{r^2}$
The correct option is B.

Unit of density and relative density are same.

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

  1. True

  2. False

Show answer
Correct Option: B
Explanation:

Unit of density is $g/cm^3$ whereas relative density is unitless. Thus the given statement is false.

Hertz is the unit of

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

  1. wavelength

  2. amplitude

  3. frequency

  4. None of these

Show answer
Correct Option: C
Explanation:

Hertz is the fundamental unit of frequency.

The SI unit of electron mobility is  :

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

  1. ${M^2}{S^{ - 1}}V - 1$

  2. $=m^2 s^{-1}V^{-1}$

  3. $m{s^{ - 1}}V$

  4. ${m^2}{s^{ - 2}}V$

Show answer
Correct Option: B
Explanation:

Electron mobility:- It is the ratio of velocity to electric field.

$\mu=\dfrac{v _e}{E}$. . . . . . .(1)
SI unit of velocity, $v _e$ $=m/s$
SI unit of electric field, $E$ $=V/m$
From equation (1),
SI unit of electron mobility is $=\dfrac{m/s}{V/m}$
$=m^2/Vs$
$=m^2 s^{-1}V^{-1}$

The dimensional formula of a physical quantity is $\displaystyle { M }^{ 1 }{ L }^{ 2 }{ T }^{ 3 }{ I }^{ -1 }$ .What is its SI unit?

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

  1. $\displaystyle { kg\quad m }^{ 2 }{ s }^{ 3 }{ A }^{ -1 }$

  2. $\displaystyle { kg\quad m }^{ 2 }{ s }^{ 2 }{ A }$

  3. $\displaystyle { kg\quad ms }^{ -3 }{ A }^{ 2 }$

  4. $\displaystyle { kg}^{2}{ m }^{ 2 }{ s }^{ 3}{ A }^{ -1 }$

Show answer
Correct Option: A
Explanation:

SI unit of $M$ is $kg$, that of $L$ is $m$, $T$ is $s$ and $I$ is $A$.
So, SI unit of $[M^1L^2T^{3}I^{-1}]$ is  $kg \ m^2s^{3}A^{-1}$.