Capacitor Question Watch

smileycat
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Report Thread starter 7 years ago
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Hi

Im stuck on a question , any help would be appreciated


A 10 F capacitor is charges to 5v and then discharged through a 5kohm resistor

Calculate how long it takes for the pd across the capacitor to fall to 4.0V?

Thanks xx
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A123W
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V=Vo(e^(-t/RC))
V/Vo=e^(-t/RC)
ln(V/Vo)=-t/RC
ln(V/Vo)*RC=-t
t=-ln(V/Vo)*RC

V=4V Vo=5V RC (time constant)=5000*10=50000

Put in the values and it should give you an answer of 11157s

Same equation applies if you need to find current or charge at a certain time, just change V and Vo to Q and Qo or I and Io. Hope this has made sense to you.
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smileycat
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Report Thread starter 7 years ago
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Thank you so much
yes that makes sense xx
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