Question

Ten identical cells each of potential ' $E$ ' and internal resistance ' $r$ ', are connected in series to form a closed circuit. An ideal voltmeter connected across three cells, will read

• A. $13E$
• B. $7E$
• C. $10E$
• D. $3E$

Answer 1

Answer: (D)

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, $V=I\times 3r$
$=\frac{E}{2}\times 3r$
$=3E$
Hence, ideal voltmeter will read $3E$.