question_answer

A galvanometer of resistance, G is shunted by a resistance S ohm. To keep the main current in the circuit unchanged, the resistance to be put in series with the galvanometer is                          

A) \[\frac{{{S}^{2}}}{(S+G)}\]          

B) \[\frac{SG}{(S+G)}\]      

C) \[\frac{{{G}^{2}}}{(S+G)}\]         

D) \[\frac{G}{(S+G)}\]

Correct Answer: C

Solution :

Current will be unchanged if resistance remains same so \[G=\frac{GS}{G+S}+R\]               \[R=G-\frac{GS}{G+S}\]                \[R=\frac{{{G}^{2}}}{G+S}\]