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