In the adjoining circuit diagram, the readings of ammeter and voltmeter are $2\, A$ and $120 \,V$, respectively. If the value of $R$ is $75\, \Omega$, then the voltmeter resistance will be $\Omega$
AIIMS 2018, Medium
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$\because V_{A B}=\left(I-I_{g}\right) R=I_{g} \cdot G$
Where, $G=$ voltmeter (resistance)
Given, $V_{A B}=120 V , I=2 A, R=75 \Omega$
$\Rightarrow 120=\left(2-I_{g}\right) 75 \Rightarrow I_{g}=0.4 A$
Now, $V_{A B}=I_{g} G \Rightarrow G=\frac{120}{0.4}=300 \Omega$
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