A voltmeter of resistance $150 \Omega$ is connected across A and B in the given circuit. The reading of voltmeter will be:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → 15 V
As 100 Ω and $R_v$ are in parallel,
$\frac{1}{R_{total}}=\frac{1}{100}+\frac{1}{R_v}$ [$R_v$ = Resistance of voltmeter]
$R_{total}=\frac{100 \times 150}{100 + 150} = \frac{15000}{250} = 60Ω$
$R_{AC}=R_{total}+100$
$=160V$
Using Ohm's law,
$I=\frac{V}{R_{AC}}$
$=\frac{40}{160}=\frac{1}{4}A$
Resistance Across galvanometer is,
$∴V_{AB}=60×\frac{1}{4}=15V$