Figure P18.40 shows several equipotential surfaces that result from a point charge at the origin. (a) If V₀ = +20 V, is this point charge positive or negative? (b) An external force moves an electron from the outermost equipotential surface drawn in Figure P18.40 to the innermost equipotential surface. If the electron starts and ends at rest, what is the work done on the electron by the external force?

Figure P18.40

 

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