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Question: Answered & Verified by Expert
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
PhysicsWork Power Energy
Options:
  • A the two magnetic forces are equal and opposite, so they produce no net effect
  • B the magnetic forces do not work on each particle
  • C the magnetic forces do equal and opposite (but nonzero) work on each particle
  • D the magnetic forces are necessarily negligible
Solution:
2724 Upvotes Verified Answer
The correct answer is: the magnetic forces do not work on each particle
When electron and proton are moving under influence of their mutual forces, then according to the flemings left hand rule, the direction of force acting on a charge particle is perpendicular to the direction of motion.
In magnetic field, work-done $=F_{.} s . \cos \theta$
$$
=F \text {. s. } \cos 90^{\circ}=0 \text {. }
$$
So magnetic forces do not work on moving charge particle.

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