# Circuit with a switch

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1. Feb 24, 2016

### Gillian

For the circuit shown in the figure, the switch S is suddenly closed with the capacitor uncharged. After one time constant, the charge on the capacitor is closest to:

a) 2.0 mC
b) 0.74 mC
c) 1.0 mC
d) 1.3 mC
e) 0.00 mC

Relevant Formulas
q = Q⋅(1-e-τ/R⋅C)
τ = RC

My Attempt
q = Q(1-e-τ/T)
q = (10⋅10-6)(1-e-1)
q = (10⋅10-6)(1-.36788)
q = (10⋅10-6)(0.632)
q = 6.32⋅10-6 C = 0.00632 mC

I am not sure how else I would approach this problem. Any suggestions?

2. Feb 24, 2016

### Orodruin

Staff Emeritus
Q is not $10^{-5}$ C.