Question

A galvanometer of resistance 100 Ω gives a full-scale deflection for a potential difference of 200 mV.

1. What must be the resistance connected to convert the galvanometer into an ammeter of the range 0-200 mA?
2. Determine resistance of the ammeter.

Answer 1

(i) Given: G = 100 Ω; I = 200 mA;

V_g = 200 mV;

Resistance to be connected to the galvanometer to convert to an ammeter:

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

Here I_g= `("V"_"g")/"G"`

= `(200 " mV")/(100  " Ω")`

= 2 mA

S = `(2 × 10^(-3) × 100)/((0.2-0.002))`

S = 1.01 Ω

(ii) `1/"R" = 1/100 + 1/1.01`

R = 0.999 Ω