A galvanometer with its coil resistance 25 Ω requires a current of 1 mA for its full deflection. In order to construct an ammeter to read up to a current of 2 A, the approximate value of the shunt resistance should be :

Question

A galvanometer with its coil resistance 25 Ω requires a current of 1 mA for its full deflection. In order to construct an ammeter to read up to a current of 2 A, the approximate value of the shunt resistance should be : (A) 2.5 × 10-3 Ω (B) 1.25 × 10-2 Ω (C) 1.25 × 10-3 Ω (D) 2.5 × 10-2 Ω

Tardigrade Admin · Accepted Answer

Given: G=25 Ω, I g =1 mA , I m =2 A So, divisions on full deflection is n=(I m /I g )=(2/0.001)=2000 We know that, shunt resistance is given by S=(G/n-1) Therefore, S=(25/2000-1) S=(25/1999)=1.25 × 10-2 Ω

Q. A galvanometer with its coil resistance $25 Ω$ requires a current of $1 m A$ for its full deflection. In order to construct an ammeter to read up to a current of $2 A$ , the approximate value of the shunt resistance should be :

$2.5 \times 10 - 3 Ω$

$1.25 \times 10 - 2 Ω$

$1.25 \times 10 - 3 Ω$

$2.5 \times 10 - 2 Ω$

Given: $G = 25 Ω, I_{g} = 1 m A, I_{m} = 2 A$
So, divisions on full deflection is
$n = \frac{I _{m}}{I _{g}} = \frac{2}{0.001} = 2000$
We know that, shunt resistance is given by $S = \frac{G}{n - 1}$
Therefore, $S = \frac{25}{2000 - 1} S = \frac{25}{1999} = 1.25 \times 1 0^{- 2} Ω$

Q. A galvanometer with its coil resistance 25Ω requires a current of 1mA for its full deflection. In order to construct an ammeter to read up to a current of 2A, the approximate value of the shunt resistance should be :

2.5×10−3Ω

1.25×10−2Ω

1.25×10−3Ω

2.5×10−2Ω