Question

Of the following quantities, which one has dimensions different from the remaining three?

A. Energy per unit volume
B. Force per unit area
C. Product of voltage and charge per unit volume
D. Angular momentum  
Answer :   Angular momentum
Solution :
$$\eqalign{ & {\text{Dimensions of energy per unit volume}} \cr & = \frac{{{\text{Dimensions of energy}}}}{{{\text{Dimensions of volume}}}} = \frac{{\left[ {M{L^2}{T^{ - 2}}} \right]}}{{\left[ {{L^3}} \right]}} = \left[ {M{L^{ - 1}}{T^{ - 2}}} \right] \cr & {\text{Dimensions of force per unit area}} \cr & = \frac{{{\text{Dimensions of force}}}}{{{\text{Dimensions of area}}}} = \frac{{\left[ {ML{T^{ - 2}}} \right]}}{{\left[ {{L^2}} \right]}} = \left[ {M{L^{ - 1}}{T^{ - 2}}} \right] \cr & {\text{Voltage}} \times \frac{{{\text{Charge}}}}{{{\text{Volume}}}} = \frac{{\left( {\frac{W}{q}} \right) \times \left( {it} \right)}}{{{l^3}}} \cr & = \frac{{\left( W \right)}}{{\left( {{l^3}} \right)}} = \frac{{\left[ {M{L^2}{T^{ - 2}}} \right]}}{{\left[ {{L^3}} \right]}} = \left[ {M{L^{ - 1}}{T^{ - 2}}} \right] \cr & {\text{Angular momentum}} \cr & = \left( r \right)\left( p \right) = \left( r \right)\left( {mv} \right) = \left[ L \right]\left[ M \right]\left[ {L{T^{ - 1}}} \right] = \left[ {M{L^2}{T^{ - 1}}} \right] \cr} $$
So, dimensions of angular momentum is different from other three.

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. $${M^{ - 1}}{L^1}{T^2}$$

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