Q. In the circuit shown, the voltage drop across the $15\, \Omega$ resistor is $30 \,V$ having the polarity as indicated. The ratio of potential difference across $5\, \Omega$ resistor and resistance $R$ is :

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A

$2 / 7$

B

$0.4$

C

$5 / 7$

D

$1$

Solution:

In the circuit shown below all the currents are indicated which can be obtained by $KCl$ at all junctions.

Writing KVL equation in closed loop we have
$+100-30-35-2 R =0$
$\Rightarrow 2 R =35 V =V_{ R } $
$\Rightarrow V_{5 \Omega} =7 \times 5=35 V$
$\Rightarrow \frac{V_{5 \Omega}}{V_{R}} =1$

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