An electron and a proton are moving under the influence of mutual forces. In calculating the change in the kinetic energy of the system during motion, one ignores the magnetic force of one on another. This is because,

Options

A. the two magnetic force are equal and opposite, so they produce no net effect.
B. the magnetic forces do no work on each particle.
C. the magnetic force do equal and opposite (but non-zero) work on each particle.
D. the magnetic forces are necessarily negligible.

Answer

B

Explanation

when electron and proton are moving under influence of their mutual forces, the magnetic force will be perpendicular to their motion hence no work is done by these forces.