A galvanometer of resistance 20 W gives a full scale deflection when a current of 0.04 A is passed through it. It is desired to convert it into an ammeter of range 20 A. The only shunt available is 0.05 W. The resistance that must be connected in series with the coil of the galvanometer is

Question

A galvanometer of resistance 20 W gives a full scale deflection when a current of 0.04 A is passed through it. It is desired to convert it into an ammeter of range 20 A. The only shunt available is 0.05 W. The resistance that must be connected in series with the coil of the galvanometer is (A) 4.95 Ω (B) 5.94 Ω (C) 9.45 Ω (D) 12.62 Ω

Tardigrade Admin · Accepted Answer

Let R be resistance connected in series with the galvanometer. From figure <img class="img-fluid question-image" alt="image" src="https://cdn.tardigrade.in/img/question/physics/42e130bed8e121430e1856ae6ea36857-.png" /> (Ig/I-Ig)=(S/G+R) R=S((I/Ig)-1)-G Substituting the given values, we get R=0.05((20/0.04)-1)-20=4.95 Ω

$4.95Ω$

$5.94Ω$

$9.45Ω$

$12.62Ω$

Let $R$ be resistance connected in series with the galvanometer.
From figure

$\frac{I _{g}}{I - I _{g}} = \frac{S}{G + R}$
$R = S (\frac{I}{I _{g}} - 1) - G$
Substituting the given values, we get
$R = 0.05 (\frac{20}{0.04} - 1) - 20 = 4.95Ω$

Q. A galvanometer of resistance 20W gives a full scale deflection when a current of 0.04A is passed through it. It is desired to convert it into an ammeter of range 20A. The only shunt available is 0.05W. The resistance that must be connected in series with the coil of the galvanometer is

4.95Ω

5.94Ω

9.45Ω

12.62Ω

Let R be resistance connected in series with the galvanometer. From figure I−Ig​Ig​​=G+RS​ R=S(Ig​I​−1)−G Substituting the given values, we get R=0.05(0.0420​−1)−20=4.95Ω

$4.95Ω$

$5.94Ω$

$9.45Ω$

$12.62Ω$

Let $R$ be resistance connected in series with the galvanometer.
From figure

$\frac{I _{g}}{I - I _{g}} = \frac{S}{G + R}$
$R = S (\frac{I}{I _{g}} - 1) - G$
Substituting the given values, we get
$R = 0.05 (\frac{20}{0.04} - 1) - 20 = 4.95Ω$