Moving Charges and Magnetism - Result Question 79

81. A galvanometer having a coil resistance of 60 $\Omega$ shows full scale deflection when a current of $1.0 amp$ passes through it. It can be converted into an ammeter to read currents upto $5.0 amp$ by

(a) putting in series a resistance of $15 \Omega$

(b) putting in series a resistance of $240 \Omega$

(c) putting in parallel a resistance of $15 \Omega$

(d) putting in parallel a resistance of $240 \Omega$

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Answer:

Correct Answer: 81. (c)

Solution:

  1. (c) $G=60 \Omega, I_g=1.0 A, I=5 A$.

Let $S$ be the shunt resistance connected in parallel to galvanometer $I_g G=(I-I_g) S$,

$S=\frac{I_g G}{I-I_g}=\frac{1}{5-1} \times 60=15 \Omega$

Thus by putting $15 \Omega$ in parallel, the galvanometer can be converted into an ammeter.