The time constant of a capacitor is 5sec. If the capacitance is C=100nF and it is charged from zero by a cell of EMF 10V through a resistor. What is the charge on it after 3 seconds?
A
4×10−7C
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B
4.5×10−7C
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C
5×10−7C
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D
5.5×10−7C
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Solution
The correct option is B4.5×10−7C Use the equation, q=CE(1−e−tRC) We know that time constant, τ=RC=5s So, At t=3, q=100×10−9×10(1−e−35) q=10−6(0.451) q=4.51×10−7C