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:

  1. (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} $