# 2 electromagnetic loops, with light-speed constraints: Is Newton's Third Law violated?

I'm a retired Physics Professor, but I admit I'm puzzled by this...

Consider two loops of wire, 2 small dipoles B and C , with a common axis z (facing each other) and (say) 30 cm apart B to C. At the speed of light, information (including a change in magnetic field) will require about 1 nanosecond to travel from C to B.

1. Have the current on in coil B for some period of time at the start, so the B-fields at C is established in the +z-direction.
2. Turn loop B off rapidly (fall time < 0.3 ns, say) at the same time that a current in loop C is turned ON (rapidly, rise time <0.3ns, and current in opposite sense with respect to the previous current in loop B).

3. In this way, as the current is turned on in loop C, it is immersed in the field from loop B and therefore it receives an impulse to the right, in the +z-direction.

However, loop B will be "off" (and open so no effective eddy currents) when the "return" field from loop C arrives.

Thus, loop C (which is free to move) will experience a force giving it momentum in the +z direction (to the right), whereas loop B will not experience a force to the left. It seems that Newton's Third Law is violated.
(The question can also be posed in momentum terms, but I chose to consider forces and the Third Law. )

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