Question

In given circuit when voltmeter is connected across $2\Omega$ gives reading 5V. When same voltmeter is connected across $3\Omega$ the reading will be

• A. 5V
• B. 7.5V
• C. 2.5V
• D. 4V

Answer 1

The correct option is B 7.5V


Let resitance of voltmeter be $R_V$.
Potential difference across $3\Omega$ is 15V.
So $I=\frac{15}{3}=5A$
By $v=iR\Rightarrow 5=i\times 2\Rightarrow i=2.5A$
$R_V=2\Omega$

$R_{eq}=\frac{6}{5}+2=\frac{16}{5}\Omega$
$\therefore I=\frac{20\times 5}{16}$
$\therefore$ potential diference across $2\Omega$ is $=\frac{20\times 5}{16}\times 2=\frac{20\times 5}{8}$
So voltmeter reading is $20-\frac{20\times 5}{8}=7.5V$