Question

In the circuit shown in figure, the ammeter shows $5A$ current, voltmeter shows $250V$ and the internal resistance of the voltmeter is $2500\Omega$, then the value of $R$ is:

• A. $150\Omega$
• B. $0.51\Omega$
• C. $510\Omega$
• D. $51\Omega$

Answer 1

The correct option is D $51\Omega$

Equivalent resistance as $R$ and $r$(internal resistance of voltmeter) connected parallel will be :

$R_{eq}=\frac{2500R}{2500+R}$

Hence, from Ohm's law, $V=250=5\left(\frac{2500R}{2500+R}\right)$

$R=\frac{2500}{49}\Omega \approx 51\Omega$