Problem 1: A galvanometer has a resistance of 50 Ohms and it deflects full scale when a current of 10mA flows in it. How it can be converted into an ammeter of range 10A?

Solution:

Step: 1 Overview

Conversion of Galvanometer into an Ammeter:
Galvanometer generally used to measure the current of very small amount. In order to measure the amount of larger currents it has to be modified into Ammeter by connecting a small amount of resistance in parallel with it, known as shunt resistance R_s.

We can change the range of an ammeter by changing the shunt resistor. To calculate how many Ohms of shunt resistor is needed for a particular range of current I, we use following equation:

R_s= (I_g/(I-I_g))R_g

where R_s is a shunt resistance, R_g is resistance of galvanometer, I_g is current passing through galvanometer and I is maximum amount of current (range) we can measure in our ammeter.

Step: 2 Calculation

Given:

R_g=50 Ohms
I=10A
I_g=10mA=0.01A

Required:

R_s=?

According to above equation:

R_s= (I_g/(I-I_g))R_g
R_s= (0.01/(10-0.01))(50)
R_s= (0.01/9.99)(50)
R_s= 0.05 Ohms (Ans)