AP · AP C:E&M · multiple choice
AP Physics C: Electricity and Magnetism · Question 1
AP Physics C: Electricity and Magnetism · Original GioPhysics question with a detailed, mark-by-mark answer guide.
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multiple choice1 mark
A solid conducting sphere of radius R carries a total charge Q distributed on its surface. What is the magnitude of the electric field at a distance r from the centre, where r < R?
- A
zero
- B
Qr/(4πε₀R³)
- C
Q/(4πε₀r²)
- D
Q/(4πε₀R²)
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Answer overviewCorrect answer: A — zero
01
1 markAnswer and reasoning
How to approach it
Predict from the governing principle before looking for a matching option. Then reject alternatives by checking direction, units, limiting behaviour or the physical meaning of each statement.
- 1
The correct choice is A: zero
- 2
B is the field inside a uniformly charged insulating sphere and is the trap: the word conducting is what decides the answer. A Gaussian surface inside a conductor in electrostatic equilibrium encloses no charge, so the field is zero.
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