Current Electricity - Result Question 40
42. The internal resistance of a $2.1 V$ cell which gives a current of 0.2 A through a resistance of $10 \Omega$ is
[2013]
(a) $0.5 \Omega$
(b) $0.8 \Omega$
(c) $1.0 \Omega$
(d) $0.2 \Omega$
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Answer:
Correct Answer: 42. (a)
Solution:
- (a) Given: $emf \varepsilon=2.1 V$
$I=0.2 A, R=10 \Omega$
Internal resistance $r=$ ?
From formula.
$\varepsilon-Ir=V=IR$
$2.1-0.2 r=0.2 \times 10$
$2.1-0.2 r=2$ or $0.2 r=0.1$
$\Rightarrow r=\frac{0.1}{0.2}=0.5 \Omega$
$ \begin{aligned} & \frac{2}{\text{ 잉 }} i=\frac{\varepsilon}{r+R} \Rightarrow 0.2=\frac{2.1}{r+10} \\ & \\ & \Rightarrow 2.1=0.2 r+2 \Rightarrow r=\frac{1}{2}=0.5 \Omega \end{aligned} $
