Question

In the question given below, a statement of Assertion (A) is given followed by a corresponding statement of Reason (R) just below it. Of the statements mark the correct answer.

Assertion (A): Power of a magnetic force on a charged particle is always zero.

Reason (R): Power of electric force on charged particle cannot be zero.

• A. Both 'A' and 'R' are true and 'R' is the correct explanation of 'A'.
• B. Both 'A' and 'R' are true and 'R' is not the correct explanation of 'A'
• C. 'A' is true and 'R' is false
• D. 'A' is false and 'R' is true

Answer 1

The correct option is C 'A' is true and 'R' is false

Power of a magnetic force , $P_b=\overrightarrow{F_b}\cdot \overrightarrow{v}$

Since, a charged particle moving in the presence of a magnetic field , moves in a circular path $\overrightarrow{F_b}\perp \overrightarrow{v}\Rightarrow P_b=0$

$\therefore$ Power of magnetic force is always zero.

But ,

Electric force ,$\overrightarrow{F_e}=q\overrightarrow{E}$

If $\overrightarrow{F_e}$ is also perpendicular to $\overrightarrow{v}$ , then its power is also zero else it is non zero.