A2L Item 219

• Description: dentify the change in charge, voltage and stored energy when a charged isolated capacitor is connected to another in parallel.
• Goal: Reason regarding capacitors
• Source: 283-545 Adding capacitors in parallel
• Keywords: Capacitors, Electromagnetism, Energy, Voltage

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The question for students:

A capacitor having, C₁, is connected to a battery until charged, then disconnected from the battery. A second capacitor, C₂, is connected in parallel to the first capacitor. Which statements below are true?

1. Charge on C1 decreases.
2. Total charge on C1 and C2 is the same as the original Q.
3. The total energy stored in both capacitors is the same as the original U stored in C1.
4. The potential (Voltage) across C1 decreases.
5. All of the above.
6. Only 1, 2, and 3 are true.
7. Only 1, 2, and 4 are true.

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Commentary for teachers:

Answer

(7) Statement #3 is the hardest for students to reason about. This is most easily decided as incorrect if the two capacitors are taken as equal.

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