Question

Six cells, each of emf $5 \,V$ and internal resistance $0.1\,\Omega$ are connected as shown in Figure. The reading of the ideal voltmeter $V$ is

• A. $30$ V
• B. $5$ V
• C. $15$ V
• D. zero
• E. $0.5 \,V$

Answer 1

Answer: (D)

$E_{\text {eff }}=\frac{E_{1} r_{2}-E_{2} r_{1}}{r_{1}+r_{2}}$
$=\frac{E(5 r)-E(r)}{6 r}$
$=\frac{2}{3} E$
As $E=5 V $
$E_{\text {eff }}=\frac{2}{3} \times 5=\frac{10}{3} V$
Reading of voltmeter $=$ Terminal potential of cell $6$
$v=5-0.1 i$
But $i=\frac{E_{\text {eff }}}{R_{\text {eff }}}=\frac{10}{0.4}=\frac{100}{4}=25\, A$
$\therefore V=5-0.1 t$
$=5-2.5=2-1 \,N$