The sensitivity of a galvanometer is 60 division /A . When a shunt is used, its sensitivity becomes 10 division/A. If the galvanometer is of resistance `20 Omega `, the value of shunt used is

Options

A. `4 Omega`
B. `5 Omega`
C. `20 Omega`
D. `2 Omega `

Answer

a

Explanation

The amount of current that causes deflection of 60 divisions in the galvanometer is 1 A, and after shunting the galvanometer same current causes deflection of 10 divisions. The current that diverts towards the shunt resistor is inversely proportional to its resistance and voltage across the salvanometer and shunt resistance is same. Hence we can write the following:
` 10 xx 20 = (60 - 10) xx S rArr S = 4 Omega` .
Thus , option (a) is correct .