An ammeter needs to be built to measure currents up to 2.0 A . If the coil has a resistance of 25 and requires 1 mA for full-scale deflection, determine the required resistance of the shunt.

Correct answer: D. 0.0125 Given, maximum current to be measured, I = 2.0 A Resistance of the galvanometer coil, R_g = 25 Current for full-scale deflection, I_g = 1 mA = 10^ -3 A The shunt resistance S required is given by the formula: S = (I_g R_g)/(I - I_g) Since I_g is very small compared to I , we can approximate I - I_g I S (I_g R_g)/(I) S = 10^ -3 × 25 2.0 S = 12.5 × 10^ -3 S = 0.0125

Concepts Of Physics MCQ Edition [Volume 2]

Exam: Concepts Of Physics MCQ Edition [Volume 2]
Subject: Physics
Chapter: Electric Current in Conductors

Concepts Of Physics MCQ Edition [Volume 2] · Physics · Electric Current in Conductors

An ammeter needs to be built to measure currents up to 2.0 A . If...

An ammeter needs to be built to measure currents up to

2.0\text{ A}

. If the coil has a resistance of

25\Omega

and requires

1\text{ mA}

for full-scale deflection, determine the required resistance of the shunt.

Options

A $0.025\Omega$
B $0.125\Omega$
C $0.05\Omega$
D $0.0125\Omega$

Correct answer

D. $0.0125\Omega$

Step-by-step solution

Given, maximum current to be measured,

I = 2.0\text{ A}

Resistance of the galvanometer coil,

R_g = 25\Omega

Current for full-scale deflection,

I_g = 1\text{ mA} = 10^{-3}\text{ A}

The shunt resistance

S

required is given by the formula:

S = \dfrac{I_g R_g}{I - I_g}

Since

I_g

is very small compared to

I

, we can approximate

I - I_g \approx I

S \approx \dfrac{I_g R_g}{I}

S = \dfrac{10^{-3} \times 25}{2.0}

S = 12.5 \times 10^{-3}\Omega

S = 0.0125\Omega

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