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?

Resistance of the galvanometer coil, G = 15 Ω

Current for which the galvanometer shows full scale deflection,

I_g= 4mA = 4 x 10⁻³ A

Range of the ammeter is 0, which needs to be converted to 6 A.

Therefore ,Current,I = 6 A

A shunt resistor of resistance S is to be connected in parallel with the galvanometer to convert it into an ammeter. The value of S is given as:

S =(I_g G)/(I -I_g) = (4 x 10⁻³ x 15)/(6 – 4 x 10⁻³)

=(6 x 10⁻² )/(6  – 0.004) = 0.06 /5.996

≈ 0.01 Ω = 10 mΩ

Hence, a shunt resistor is to be connected in parallel with the galvanometer.