Question

Two cells $\varepsilon_{1}$ and $\varepsilon_{2}$ connected in opposition to each other as shown in figure.

The cell $\varepsilon_{1}$ is of emf $9 \,V$ and internal resistance $3\,\Omega$ the cell $\varepsilon_{2}$ is of emf $7 \,V$ and internal resistance $7\,\Omega$. The potential difference between the points $A$ and $B$ is

• A. $8.4\,V$
• B. $5.6\,V$
• C. $7.8\,V$
• D. $6.6\,V$

Answer 1

Answer: (A)

$I=\frac{\Delta\varepsilon}{r_{1}+r_{2}}=\frac{9-7}{3+7}$
$=\frac{2}{10}=0.2\,A$
Potential difference across cell $\varepsilon_{1}$ is
$=9-0.2 \times 3$
$=9-0.6=8.4\,V$
Potential difference across $\varepsilon_{2}$ :
$V_{AB}=\varepsilon_{2}+0.2\,r_{2}=7+0.2\times7=7$
$=7+1.4=8.4\,V$