PhysicsLAB AP Free Response Question
2000 B3

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Three identical resistors, each with resistance R, and a capacitor of 1.0 x 10-9 F are connected to a 30 V battery with negligible internal resistance, as shown in the circuit diagram above. Switches S1 and S2 are initially closed, and switch S3 is initially open. A voltmeter is connected as shown.
 (a) Determine the reading on the voltmeter.

 (b) Switches S1 and S2 are now opened, and then switch S3 is closed. Determine the charge Q on the capacitor after S3 has been closed for a very long time.

(c) After the capacitor is fully charged, switches S1 and S2 remain open, switch S3 remains closed, the plates are held fixed, and a conducting copper block is inserted midway between the plates, as shown below. The plates of the capacitor are separated by a distance of 1.0 mm, and the copper block has a thickness of 0.5 mm.
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 i. What is the potential difference between the plates?

 ii. What is the electric field inside the copper block?

 iii. On the diagram above, draw arrows to clearly indicate the direction of the electric field between the plates.

 iv. Determine the magnitude of the electric field in each of the spaces between the plates and the copper block.

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