Question

Consider the diagram shown below. A voltmeter of resistance $150 \,\Omega$ . is connected across $A$ and $B$. The potential drop across and $C$ measured by voltmeter is

• A. 29 V
• B. 27 V
• C. 31 V
• D. 30 V

Answer 1

Answer: (C)

31 V

Answer 2

When voltmeter is connected across $A$ and $B$, the equivalent resistance of the circuit is $R_{e q} =100+\frac{150 \times 100}{100+150}$ $=100+\frac{15000}{250}$ $=100+60=160\, \Omega$ $\therefore$ Current, $i =\frac{50}{160}=\frac{5}{16} A$ . Therefore, potential drop across $B$ and $C$ is $V_{B C} =i R_{B C}$ $=\frac{5}{16} \times 100$ $=\frac{500}{16}=31.25 \,V$