Question

A galvanometer of resistance 100 Ω gives a full-scale deflection for a current of 10⁻⁵ A. To convert it into an ammeter capable of measuring up to 1 A we should connect a resistance of ______.

Options

• 1 Ω in parallel

• 10⁻³ Ω in parallel

• 10⁵ Ω in series

• 100 Ω  in series

Answer 1

A galvanometer of resistance 100 Ω gives a full-scale deflection for a current of 10⁻⁵ A. To convert it into an ammeter capable of measuring up to 1 A we should connect a resistance of 10⁻³ Ω in parallel.

Explanation:

Here, R_g = 100 Ω; I_g = 10⁻⁵ A; I = 1A; S = ? 

S = `("I"_"g""R"_"g")/("I" - "I"_"g")`

= `(10^-5 xx 100)/(1 - 10^-5)`

= 10⁻³ Ω in parallel