Question

Question 4.28: A galvanometer coil has a resistance of 15 Ω and the metre shows full scale deflection for a current of 4 mA. How will you convert the metre into an ammeter of range 0 to 6 A?

Class 12 - Physics - Moving Charges And Magnetism Moving Charges And Magnetism Page-172

Answer 1

To converts galvanometer into ammeter of required range , we should join join shunt in parallel combination with galvanometer metre.
Let G is the resistance of galvanometer.
S is the resistance of shunt join in parallel with galvanometer.
$I_g$ is the current passing through galvanometer. and I is the maximum range of current.
now, $S=\frac{I_gG}{I-I_g}$
here, Ig = 4mA = 4 × 10^-3A
I = 6A , G = 15 ohm

now, $S=\frac{4\times10^{-3}\times15}{6-4\times10^{-3}}=0.01\Omega$

Answer 2

Explanation:

Here your answer...

G=15Ω

Current for which, the galvanometer shows full scale deflection, i=4mA.

Range of ammeter is 4 mA, which needs to be converted to 6A.

∴I=6A

A short resistance R is to be connected in parallel to the galvanometer.

R=iG/(I−i)=10mΩ