My professor taught us in a theory lecture on electromagnetism , that if two charges are 1 light year apart and the charge on the left moves towards the charge on the right. The force felt on the right charge will "instantaneously" change however the force felt on the left will take 1 light year to change. Why are both forces on both charges not changed by the same amount since the radius is lower for both charges hence both forces should experience increase in force according to coulombs law? Thank you
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Each charge feels a force due to the electric field of the other charge. Changes in this electric field propagate outward at the speed of light.
When you move one charge toward the other, the electric field that the moved charge sees from the stationary charge is different because the moved charge is now at a different distance from the stationary charge. Therefore, the magnitude of the force on the moved charge is different instantaneously, as the field of the stationary charge was always there.
On the other hand, the stationary charge will only feel a different force once the change in the moved charge's electric field propagates to its location. As such, it will experience a change in force later than the moved charge.
probably_someone
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Thank you for an amazing explanation , this now makes complete sense !! :) – HMMAXI Apr 06 '18 at 22:24
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Cool! If that's the case, you should accept this answer. – probably_someone Apr 06 '18 at 22:41
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1Sorry I am a bit new to stack exchange , I have accepted your answer. Thx – HMMAXI Apr 06 '18 at 22:46