Question

The ratio of the dimensions of Planck’s constant and that of the moment of inertia is the dimension of

A. frequency  
B. velocity
C. angular momentum
D. time
Answer :   frequency
Solution :
$$\eqalign{ & {\text{Energy carried by photon is given by }}E = hv \cr & \Rightarrow h = {\text{Planc's constant}} = \frac{E}{v} \cr & \therefore \left[ h \right] = \frac{{\left[ {M{L^2}\;{T^{ - 2}}} \right]}}{{\left[ {{T^{ - 1}}} \right]}} = \left[ {M{L^2}\;{T^{ - 1}}} \right] \cr & {\text{and}}\,I = {\text{moment of inertia }} = M{R^2} \cr & \Rightarrow \left[ I \right] = \left[ {M{L^2}} \right] \cr & {\text{Hence,}}\,\frac{{\left[ h \right]}}{{\left[ I \right]}} = \frac{{\left[ {M{L^2}\;{T^{ - 1}}} \right]}}{{\left[ {M{L^2}} \right]}} = \left[ {{T^{ - 1}}} \right] \cr & = \frac{1}{{[\;T]}} = {\text{dimension of frequency}} \cr} $$
Alternative
$$\eqalign{ & \frac{h}{I} = \frac{{\frac{E}{v}}}{I} \cr & = \frac{{E \times T}}{I} = \frac{{\left( {\frac{{kg - {m^2}}}{{{s^2}}}} \right) \times s}}{{\left( {kg - {m^2}} \right)}} \cr & = \frac{1}{{\;s}} = \frac{1}{{{\text{ time }}}} = {\text{frequency}} \cr} $$
Thus, dimensions of $$\frac{h}{I}$$ is same as that of frequency.

Releted MCQ Question on
Basic Physics >> Unit and Measurement

Releted Question 1

The dimension of $$\left( {\frac{1}{2}} \right){\varepsilon _0}{E^2}$$  ($${\varepsilon _0}$$ : permittivity of free space, $$E$$ electric field)

A. $$ML{T^{ - 1}}$$
B. $$M{L^2}{T^{ - 2}}$$
C. $$M{L^{ - 1}}{T^{ - 2}}$$
D. $$M{L^2}{T^{ - 1}}$$
Releted Question 2

A quantity $$X$$ is given by $${\varepsilon _0}L\frac{{\Delta V}}{{\Delta t}}$$   where $${ \in _0}$$ is the permittivity of the free space, $$L$$ is a length, $$\Delta V$$ is a potential difference and $$\Delta t$$ is a time interval. The dimensional formula for $$X$$ is the same as that of-

A. resistance
B. charge
C. voltage
D. current
Releted Question 3

A cube has a side of length $$1.2 \times {10^{ - 2}}m$$  . Calculate its volume.

A. $$1.7 \times {10^{ - 6}}{m^3}$$
B. $$1.73 \times {10^{ - 6}}{m^3}$$
C. $$1.70 \times {10^{ - 6}}{m^3}$$
D. $$1.732 \times {10^{ - 6}}{m^3}$$
Releted Question 4

Pressure depends on distance as, $$P = \frac{\alpha }{\beta }exp\left( { - \frac{{\alpha z}}{{k\theta }}} \right),$$     where $$\alpha ,$$ $$\beta $$ are constants, $$z$$ is distance, $$k$$ is Boltzman’s constant and $$\theta $$ is temperature. The dimension of $$\beta $$ are-

A. $${M^0}{L^0}{T^0}$$
B. $${M^{ - 1}}{L^{ - 1}}{T^{ - 1}}$$
C. $${M^0}{L^2}{T^0}$$
D. $${M^{ - 1}}{L^1}{T^2}$$

Practice More Releted MCQ Question on
Unit and Measurement


Practice More MCQ Question on Physics Section