The Electric Field in Various Circumstances: Feynman's Physics Explained
When conductors are present, charges shuffle around until the surface is all at one potential, which makes problems tricky. A clever fix is the 'method of images': to find the field of a charge near a conducting plane, pretend the plane is gone and place an imaginary mirror-image charge on the other side. The field in the real region comes out exactly right. At sharp points the field grows very strong — which is why lightning rods are pointed.
The big idea
An imaginary 'mirror charge' can solve a hard conductor problem.
Think about it
Why does charge — and electric field — pile up most at the sharp tip of an object?
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