A point charge +Q is placed inside a thin, uncharged metallic spherical shell but not at its center. What is the electric force experienced by the charge +Q?

Zero
directed in rightward direction
directed in leftward direction
direction can't be determined

Correct answer: directed in rightward direction

Solution

An off-center charge inside a metallic shell induces non-uniform negative charges on the inner surface. The net electrostatic force on +Q due to these induced charges is directed toward the nearest wall of the shell (attractive image force). The force is not zero and not undetermined; it depends on the displacement shown in the figure. For a figure showing Q displaced rightward, the force is directed rightward.

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