devarshi-dt-logo

Question:

To know the resistance G of a galvanometer by half deflection method, a battery of emf V and resistance R is used to deflect the galvanometer by angle θ. If a shunt of resistance S is needed to get half deflection then G, R and S are related by the equation?

S(R+G)=RG

2S=G

2S(R+G)=RG

2G=S

Solution:

After applying shunt S, deflection gets halved, hence current gets halved. Hence,
(1/2)V/(R+G) = V/(R+G/S)
G/(G+S) = (1/2)V/(R+G)
Solving this gives S(R+G)=RG.