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CBSE Class 12 Physics 2016 Outside Delhi Set 1 Paper

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Question : 10 of 26
Marks: +1, -0
A battery of emf 12 V12\,\text{V} and internal resistance 2 Ω2\,\Omega is connected to a 4 Ω4\,\Omega resistor as shown in the figure.
(a) Show that a voltmeter when placed across the cell and across the resistor, in turn, gives the same reading.
(b) To record the voltage and the current in the circuit, why is voltmeter placed in parallel and ammeter in series in the circuit?
Solution:  
(a) Relation for terminal potential
(b) Justification
(c) Explanation (parallel and series)
(a) Effective resistance of the circuit RE=6 ΩR_E=6\,\Omega
∴    VI=  12 A6=2 A\therefore \;\; V I=\;\frac{12\,\text{A}}{6}=2\,\text{A}
Terminal potential difference across the cell, VV =E=E -ir
Also p.d. across 4 Ω4\,\Omega resistor =4×2 V=8 V=4 \times 2\,\text{V}=8\,\text{V}
Hence the voltmeter gives the same reading in the two cases.
(b) In series - current same
In parallel-potential same
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