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What is the ratio of the electrostatic force between two charges held a fixed distance apart in vacuum to the force between the same charges at the same separation inside a medium of permittivity epsilon?

1. epsilon: epsilon0
2. epsilon0: epsilon
3. 1: epsilon
4. epsilon: 1

Correct answer: epsilon: epsilon0

Solution

Force F = q1*q2 / (4*pi*permittivity*r²). With charges and distance fixed, F is inversely proportional to the permittivity, so the ratio of forces is the inverse ratio of permittivities.

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