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  4. In the adjoining circuit, the emf of the cell is 2 volt and the internal resistance is negligible. The resistance of the voltmeter is 80 ohm. The reading of the voltmeter will be

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Q. In the adjoining circuit, the emf of the cell is $2 $ volt and the internal resistance is negligible. The resistance of the voltmeter is $80\, ohm$. The reading of the voltmeter will bePhysics Question Image

Current Electricity

Solution:

Total resistance of the circuit $=\frac{80}{2}+20=60\, \Omega$
$\Rightarrow $ Main current, $i=\frac{2}{60}=\frac{1}{30} A$
Combination of voltmeter and $80\, \Omega$ resistance is connected in series with $20\, \Omega$, so current through $20\, \Omega$ and this combination will be same, i.e., $\frac{1}{30} A$.
Since the resistance of voltmeter is also $80 \,\Omega$, so this current is equally distributed in $80\, \Omega$ resistance and voltmeter (i.e., $\frac{1}{60}$ A through each)
Potential difference across. $80 \,\Omega$ resistance $=\frac{1}{60} \times 80=1.33\, V$