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In the circuit shown below, the reading of the voltmeter V is
A.12V
B.8V
C.20V
D.16V
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Answer
VerifiedVerified
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Hint: As we can see, the two resistors which are connected to the voltmeter are connected in parallel. So, first find the potential difference along the path where the 4Ω resistor is connected. Then, find the potential difference along the path where the 16Ω resistor is connected. Subtract these two potential differences and find the reading on the voltmeter V. To find the potential across the resistor use Ohm’s law.

Complete answer:
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Let the potential at point A be VA
Potential difference across points A and C is given by,
VAC=VAVC …(1)
From Ohm’s law we know,
V=IR
Therefore, potential across 4Ω resistance is.
VC=1×4
VC=4V
Substituting this value in the equation. (1) we get,
VAC=VA4 …(2)
Similarly, potential difference across points A and D is given by,
VAD=VAVD …(3)
Potential across 16Ω resistance is.
VD=1×16
VC=16V
Substituting this value in the equation. (1) we get,
VAD=VA16 …(4)
Thus, potential difference across points C and D is given by,
VCD=VACVAD
Substituting equation. (2) and (4) in above equation we get,
VCD=VA4VA+16
VCD=164
VCD=12V
Hence, the reading of the voltmeter V is 12V.

So, the correct answer is option A i.e. 12V.

Note:
When the resistors are connected in series, there is only one path for the current to flow. Thus, equal current flows through each resistor. But, the potential drop across all the resistors in series may not be the same.
When the resistors are connected in parallel, there are many paths for the current to flow. The current may not be the same through each path in the circuit. But, the potential drop across all the resistors connected in parallel is the same.
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