Ncert Exercises & Solutions

Consider a simple circuit shown in the figure. $R'$ stands for variable resistance. $R'$ can vary from $R_0$ to infinity. $r$ is the internal resistance of the battery $(r<<R<<R_0)$ .

(a)	Potential drop across $AB$ is nearly constant as $R'$ is varied.
(b)	Current through $R'$ is nearly constant as $R'$ is varied.
(c)	Current $I$ depends sensitively on $R'$ .
(d)	$I \geq { \dfrac V {r+R}}$ always.

Which among the following statements is correct?

1.	(a, c)	2.	(a, d)
3.	(b, d)	4.	(c, d)

(2) Hint: The resistance in AB and R' are in parallel combination.

Here, the potential drop is taking place across AB and r. Since the equivalent resistance of the parallel combination of R' and r is always less than R, therefore,

I \geq \frac{V}{r + R}

$I \geq \frac{V}{r + R}$ always.

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