First slide

voltmeter

Question

Resistances R₁ and R₂, each of $60 Ω,$ are connected in series as shown in figure. The potential difference between A and B is kept 120 volt. what will be the reading of voltmeter connected between the points C and D if resistance of voltmeter is $120 Ω ?$

Moderate

A

48 V
B

24 V
C

40 V
D

None

Solution

R₂ and R_V are in parallel, their equivalent is
${R^{'}}_{2} = \frac{R_{2} R_{V}}{R_{2} + R_{V}} = \frac{60 \times 120}{60 + 120} = 40 Ω$
Now, $I = \frac{120}{R_{1} + {R^{'}}_{2}} = \frac{120}{60 + 40} = 1 .2 A$
Reading of voltmeter
$= I {R^{'}}_{2} = 1 .2 \times 40 = 48 V$

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