question_answer

A shunt of resistance 1\[\Omega \] connected across a galvanometer of 120\[\Omega \]resistance. A current of 5.5 ampere gives full scale deflection in the galvanometer. The current that will give full scale deflection in the absence of the shunt is nearly:                   [JEE ONLINE 09-04-2013]

A) 5.5 ampere

B) 0.5 ampere

C)             0.004 ampere

D) 0.045 ampere

Correct Answer: D

Solution :

[d]

\[{{r}_{A}}=\frac{l\times 120}{120+1}=\frac{120}{121}=1\,\,\Omega \]

\[V=l(R+1)\]

\[V=5.5(R+1)\]

Without short resistance

\[V=l'(R+120)\]                      ...(ii)

Eq. (i) is equal to Eq. (ii)

\[5.5(R+1)=l'(R+120)\]

Hence, if the circuit has no resistance \[R=0\]

\[5.5=l'(120)\]\[l'=\frac{5.5}{120}=0.045\,A\]