Question

The resistor in an RC circuit has a resistance of 155 Ω .

Part A

What capacitance must be used in this circuit if the time constant is to be 4.2 ms ?

Express your answer using two significant figures.

C C =		μF

Part B:

Using the capacitance determined in part (a), calculate the current in the circuit 8.4 ms after the switch is closed. Assume that the capacitor is uncharged initially and that the emf of the battery is 9.0 V.

Express your answer using two significant figures.

Answer 1

Past-A In case of Rc-Cirenit, the quantity CR = 2 has the dimension of time and is called the time constant of the elrenit. 7 CR= Q I Giron - & - 1 7= 4.2ms R = 1550 7ės = 4.2x103 155 >> C= 0.0271X103 --6 TO FINE a) c = 21.1x10 6 t. - c = 27.1 NF ~ 2T NE past-B: RR +11 mmo ve tue In the case of c- cirlint we have the expression of sate of charging or instantaneous enirent is, Given, i do other t= 8.4 ms CR=4.2005 & a v – HER = &-9.00 Raws to v 155e.4.2 > i 90 x 0 2 -1.9x103 . 9MA i = 7.9 mA