Question: Q. 19. A battery of emf $E$ and internal resistance $r \mathrm{ohm}$ when connected across an external resistance of $5 \Omega$, produces a current of $1 \mathrm{~A}$. When connected across a resistance of $11 \Omega$, it produces a current of $0.5 \mathrm{~A}$. Determine (i) the emf and (ii) the internal resistance of the cell.
A [O.D. Comptt. I, II, III 2013]
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Solution:
Ans. Try yourself, Similar to Q. 18, Short Answer Type-I
[A] Q. 20. A battery of emf $10 \mathrm{~V}$ and internal resistance $3 \mathrm{ohm}$ is connected to a resistor. If the current in the circuit is $0.5 \mathrm{~A}$, find :
(i) the resistance of the resistor;
(ii) the terminal voltage of the battery.
A [Delhi Comptt. I, II, III 2012]
Ans. Given : $E=10 \mathrm{~V}, r=3 \Omega, I=0.5 \mathrm{~A}, R=$ ?, $V=$ ?
(i) $\because$
$$ I=\frac{E}{R+r} $$
$$ \Rightarrow \quad R+r=\frac{E}{I}=\frac{10}{0.5}=20 \Omega $$
or $\quad R=20-r$
$$ R=20-3=17 \Omega $$
(ii)
$$ V=I R=0.5 \times 17=8.5 \mathrm{~V} $$
