In the circuit (Fig.) the current is to be measured. What is the value of the current if the ammeter shown (a) is a galvanometer with a resistance `R_(G)=60.00 Omega,` (b) is a galvanometer described in (a) but converted to an ammeter by a shunt resistance `r_(s)=0.02 Omega,` (c) is an ideal ammeter with zero resistance ?

Explanation

a) Total resistance in the circuit is,
`R_(G)+3=63 Omega.` Hence I=3/63=0.048 A.
b) Resistance of the galvanometer converted to an ammeter is,
`(R_(G) r_(s))/(R_(G)+r_(s))=(60 Omega xx0.02 Omega)/((60+0.02))=0.02 Omega`
Total resistance in the circuit is,
`0.02 Omega + 3 Omega=3.02 Omega.` Hence I=3/3.02=0.99 A.
c) For the ideal ammeter with zero resistance
I=3/3=1.00 A