Question

When a resistor of 2 $\Omega$ is connected across the terminals of a battery a current of $2A$ is found to flow. When a second resistor of $8\Omega$ is connected in series with the first, the current is reduced to $1A$. The emf and internal resistance of the battery are

• A. 12V, 4$\Omega$
• B. 10V, 2$\Omega$
• C. 16V, 6$\Omega$
• D. 16V, 4$\Omega$

Answer 1

The correct option is C 16V, 6$\Omega$

Case 1

$E=2[2+r]$ ............(1)
Case 2

$E=1[10+r]$ ...........(2)
By equating (1) and (2)
$10+r=4+2r$
$r=6\Omega$
$E=2\left(8\right)$

$=16V$
$E=16V$

$r=6\Omega$