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Question

In the given circuit the internal resistance of the 18 V cell is negligible. If R1=400 Ω,R3=100 Ω and R4=500 Ω and the reading on an ideal voltmeter across R4 is 5 V, then the value of R2 will be


A
230 Ω
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B
300 Ω
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C
450 Ω
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D
550 Ω
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Solution

The correct option is B 300 Ω


Reading of voltameter across R4,
V4=5 V
So, current throgh R4,
i1=V4R4=0.01 A
Voltage across R3,
V3=i1R3=0.01×100=1 V
Total voltage
V3+V4=6 V=V2
From circuit, we can write-
V1+V3+V4=18 V
V1=12 V
i=V1R1=0.03 A
Using KCL,

i=i1+i2i2=ii1=0.030.01 A=0.02 A
R2=V2i2=60.02=300 Ω

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