Question

A galvanometer coil has a resistance of 15 W and the metre showsfull scale deflection for a current of 4 mA. How will you convert themetre into an ammeter of range 0 to 6 A?

Answer 1

Given: The resistance of the galvanometer coil is 15 Ω, the magnitude of current for the full scale deflection is 4 mA and the range of the ammeter is 0 to 6 A.

The resistance of resistor connected in parallel is given as,

S= I g G I− I g

Where, the resistance of the galvanometer coil is G, the full scale deflection is I g , the maximum limit of current is I.

By substituting the given values in the above equation, we get

S= 4× 10 −3 ×15 6−4× 10 −3 = 60× 10 −3 6−0.004 =0.01 Ω =10 mΩ

Thus, the resistance of resistor which has to be connected in parallel with the galvanometer is 10 mΩ.