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2

There is no tangential force. Both forces due to the central charge on the circumferential charges are exactly radial. So they have no effect on moving the charges on the ring.

3

Coherent versus incoherent is a red herring here. There isn't any fundamental difference between gravitational and electromagnetic waves, either. The facts are the following: For both coherent and incoherent waves, whether electromagnetic or gravitational, the typical intensity falls off as $1/r^2$, and the typical amplitude falls off as $1/r$. For a white ...

3

It is a convention that the dipole moment of a system of one positive charge and one negative charge points in the direction from the negative one to the positive one. Instead of seeing this as being opposite to the direction of the field along the axis between them, see it as indicating the direction the field sprouting out of the “top” of the dipole, past ...

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