Magnetics 6 Question 4
4. The resistance of a galvanometer is $50 ohm$ and the maximum current which can be passed through it is $0.002 A$. What resistance must be connected to it in order to convert it into an ammeter of range $0-0.5 A$ ?
(a) $0.2 ohm$
(b) $0.5 ohm$
(c) $0.002 ohm$
(d) $0.02 ohm$
(2019 Main, 9 April II)
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Solution:
- Key Idea An ammeter is a type of galvanometer with a shunt connected in parallel to the galvanometer.
Ammeter circuit is shown in the figure below,
So,
Here,
$$ I _g G=\left(I-I _g\right) S $$
$$ \begin{aligned} I _g & =0.002 A \\ I & =0.5 A, \end{aligned} $$
$$ G=50 \Omega $$
So, shunt resistance required is
$$ S=\frac{I _g G}{I-I _g}=\frac{0.002 \times 50}{(0.5-0.002)} \approx 0.2 \Omega $$
