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In a circuit, key K1 is initially open and a capacitor C is in steady state with charge q1. When K1 is closed and a new steady state is reached, the charge on C becomes q2. The ratio q1/q2 is:

1. 5/3
2. 3/5
3. 1
4. 2/3

Correct answer: 3/5

Solution

With K1 open, C charges to a voltage determined by one resistor arrangement; with K1 closed, an additional parallel path alters the effective voltage, changing the charge on C. A standard version of this circuit gives q1/q2 = 3/5.

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