Question

The resistance of a voltmeter is 100 $\Omega$. It is connected to a 12V-20W battery. The reading of voltmeter is (Nearly)

• A. 6V
• B. 8V
• C. 9V
• D. 11V

Answer 1

Answer: (D)

11V

$\frac{V^2}{r}=20W$

$\Rightarrow r=\frac{144}{20}=7-2\Omega$ [r is internal resistance]

$I=[r+R_{volt}]=12$

$I=\frac{12}{107.2}$

Reading of voltmeter $=R_{volt}$

$=\frac{12}{107.2}\times 100=11.19\approx 11V$