Q1 of 48 Page 38

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,

From work energy theorem, we know that change in kinetic energy of the system is equal to work done by net force acting on the system. According to the question, the magnetic forces due to motion of an electron and a proton act in perpendicular direction to the direction of motion which results in the centripetal force for the particle and hence particle performs uniform circular motion (i.e.; speed of the particle remains constant)


∴ no work is done by the forces and so no change in K.E. of the particle.


Hence, magnetic forces do no work on each particle.


Option (b) is correct.

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