Question

Assertion :A resistance $R$ is connected between the two ends of the parallel smooth conducting rails. A conducting rod lies on these fixed horizontal rails and a uniform constant magnetic field $B$ exists perpendicular to the plane of the rails as shown in figure. If the rod is given a velocity $v$ and released as shown in figure, it will stop after some time. The total work done by magnetic field is negative. Reason: If force acts opposite to direction of velocity, its work done is negative.

• A. Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
• B. Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion
• C. Assertion is correct but Reason is incorrect
• D. Assertion is incorrect but Reason is correct

Answer 1

The correct option is D Assertion is incorrect but Reason is correct

Work done by magnetic field is always zero.
The magnetic force $q(\overrightarrow{v}\times \overrightarrow{B})$ is normal to $\overrightarrow{v}$ and work done by it is zero.
Hence Statement 1 is false.