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Question:

Consider the diagram shown below. A voltmeter of resistance 150Ω is connected across A and B. The potential drop across B and C measured by the voltmeter is?

29 V

27 V

30 V

31 V

Solution:

When a voltmeter of resistance 150Ω is connected across A and B, the resistance across A and B will be
Rab = (150 × 100) / (150 + 100) = 60Ω
Now the equivalent resistance of the circuit will be
Rac = Rab + Rbc = 60 + 100 = 160Ω
The current in the circuit will be
I = 50 / 160 = 0.31 A
Thus, Potential drop across B and C will be
Vbc = IRbc = (0.31)(100) = 31 V