Question

10 identical cells each of emf E and internal resistance r, are connected in series to form a closed circuit. An ideal voltmeter connected across 3 cells will read:

• A. 7E
• B. 13E
• C. 3E
• D. 10E

Answer 1

Answer: (C)

10 identical cells connected in series.
Potential of each cell $=E$
Internal resistance of each cell $=r$
Total voltage of ten cells $=10E$
Total resistance of ten cells $=10r$
Current in the circuit, $I=\frac{10E}{10r}=\frac{E}{r}$
Potentiol difference across 3 cells, $V=I\times 3r$
$<br/>=\frac{E}{2}\times 3r<br/>$
$<br/>=3E<br/>$
Hence, ideal voltmeter will read $3E$.