AP · AP C:E&M · multiple choice
AP Physics C: Electricity and Magnetism · Question 3
AP Physics C: Electricity and Magnetism · Original GioPhysics question with a detailed, mark-by-mark answer guide.
- Demand
- routine
- Marks
- 1
- Topics
- 1
- Answer
- Complete
In a series RC circuit connected to a battery of e.m.f. ε at t = 0 with the capacitor initially uncharged, what are the current immediately after the switch is closed and a long time later?
- A
ε/R immediately, and zero a long time later
- B
zero immediately, and ε/R a long time later
- C
ε/R at both times
- D
zero at both times
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Answer and reasoning
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: ε/R immediately, and zero a long time later
- 2
B is the answer for an inductor rather than a capacitor. An uncharged capacitor has no potential difference across it, so at the first instant it behaves as a wire; once charged to ε it blocks any further current.
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