A 50 microFarad capacitor is fed with a current of 25 milliAmpere. How long will it take to charge it to 100Volts?
- 1 second.
- 0.2 seconds.
- 12 minutes.
Explanation
Find the circuit resistance from the given current: R = V / I = 100 V / 0.025 A = 4000 ohms. Time constant TC = R x C = 4000 ohms x 50 uF = 0.2 s. A capacitor is treated as fully charged after 5 time constants, so the charge time = 5 x TC = 5 x 0.2 s = 1 second. Note: 0.2 s is only one time constant (and also what Q = I x t gives) - that is the common distractor, not the answer.
vilkas90 asking:
How to find it?
Community Comments (1)
D
dimky Posts: 514 27.11.2016 / 14:31
Work out the resistance in the circuit first: R=V/I=100/0.025=4000 ohms
Then work out the time constant: TC=R*C=4000*0.00005=0.2
Time to charge = 5RC = 5 * 0.2 = 1
Then work out the time constant: TC=R*C=4000*0.00005=0.2
Time to charge = 5RC = 5 * 0.2 = 1
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