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 Main Online Paper (Held On 09 April 2013)      

A)                 5.5 ampere                                        

B)                 0.5 ampere                                        

C)                 0.004 ampere                   

D)                 0.045 ampere                

Correct Answer: D

Solution :

                                \[{{r}_{A}}=\frac{l\times 120}{120+1}=\frac{120}{121}=1\,\,\Omega \]                                 \[V=l(R+1)\]                 \[V=5.5(R+1)\]                 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 \[R=0\]                 \[5.5=l'(120)\]\[l'=\frac{5.5}{120}=0.045\,A\]