Question

When the key K is pressed at time t = 0, then which of the following statement about the current I in the resistor AB of the given circuit is true?

• A. I oscillates between 1 mA and 2 mA
• B. at t = 0, I = 2 mA and with time it goes to 1 mA
• C. I= 1 mA at all t
• D. I= 2 mA at all t.

Answer 1

Answer: (B)

Initially, the current will pass through the
capacitor (and not through the resistance which is
parallel to capacitor). So effective resistance in the
circuit is $R_{AB}$. Therefore the current in the resistor
is 2 mA. After some time, the capacitor will become
fully charged and will be in its steady state. Now
no current will pass through the capacitor and the
effective resistance of the circuit will be (1000 +
1000) = 2000 $\Omega$. Therefore current in the resistor
$=\frac{V}{R}=\frac{2}{2000}=1\times 10^{-3}A=1mA.$