@JohnRennie Hello sir, I was reading about electromagnetic theory from Feynman lectures, and I came across this equation for electric field: $$E=\frac{-q}{4\pi\epsilon}\biggl[
\frac{e_{r'}}{r'^2}+\frac{r'}{c}\,\frac{d}{dt}\biggl(
\frac{e_{r'}}{r'^2}\biggr)+\frac{1}{c^2}\,\frac{d^2}{dt^2}\,e_{r'}
\biggr]$$

Where $$e_{r'}$$ is the apparent direction of the charge from a point.

While explaining the 3rd term near eqn 28.5, He says "What this term says is: look at the charge and note the direction of the unit vector (we can project the end of it onto the surface of a unit sphere). As the charg…