First slide

CIrcuit questions

Question

In the arrangement shown, reading of the ammeter just after the switch S is closed is 2 Amp and a long time after S is closed, the reading is 0.5 A. Then the value of R is

Moderate

A

$50 Ω$
B

$150 Ω$
C

$100 Ω$
D

$200 Ω$

Solution

(2)
Just after S is closed, no current flows through R and full current flows through the capacitor.
$∴ \frac{E}{50} = 2 ..... (1)$
A long time after S is closed, capacitor becomes fully charged, it does not allow any current to pass through it and full current flows through R.
$∴ \frac{E}{50 + R} = 0.5 ..... (2)$
$(1) \div (2) \Rightarrow \frac{50 + R}{50} = \frac{2}{0.5} \Rightarrow R = 150 Ω$

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