First slide

CIrcuit questions

Question

In the diagram shown, reading of the ammeter just after closing the switch S is 12 A and a long time after S is closed is 4 A. Then value of ‘R’ is

Moderate

A

4 $Ω$
B

1 $Ω$
C

6 $Ω$
D

2 $Ω$

Solution

Just after S is closed, charge on the capacitor is zero. So equivalent resistance $= (\frac{2 R}{2 + R}) Ω$
$∴ \frac{E}{2 R / (2 + R)} = 12 \Rightarrow (2 + R) E = 24 R ..... (1)$
A long time after S is closed, the capacitor becomes fully charged. There fore $\frac{E}{2} = 4 \Rightarrow E = 8 volt ...... (2)$
$∴ (2 + R) 8 = 24 R \Rightarrow R = 1 Ω$

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