Q) In the figure shown, the switch is closed at t=0. Find potential difference accross the resistance R=20ohm , 1millisecond after closing the switch

 

 

in a RC circiut if PD after a specified time is given . we shld apply KVL thru the loop and formulate a differential quation of q (charge of the capacitor at any time t) and then differentiate that equation to get the current in terms of time t. thus we can find the PD across the resistance
i think

applying KVL in that loop containg the 20ohm resistance and 40microF capacitor and battery we get

q/C + 30i = 20

i= dq/dt

thus in solving the differential equation we get
q= EC(1- e^(-t/RC))

E=20V

C= 40micro F

R=30 ohm

on differentiating this equation wrt t we get

i = Ee^(-t/RC) /R

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