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PRACTICE / Electrostatic conductors

Move within an empty conducting shell

An isolated spherical conducting shell of radius 0.30 m carries +9 nC. Its cavity contains no charge before a negligibly small test probe is introduced. External fields are absent.

In the test-charge limit, what is the source potential at the centre?

Organize the givens & assumptions
  • Shell radius: 0.30 m
  • Shell charge: +9 nC

Fixed point sources in vacuum; k = 9.0×10⁹ N m²/C². Ignore the probe’s effect on the sources. Zero potential at infinity. Electrostatic equilibrium. The test probe does not measurably rearrange the shell charge.

  1. A270 V270\ \mathrm V
  2. B0 V0\ \mathrm V
  3. C900 V900\ \mathrm V
  4. D27 V27\ \mathrm V

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