Discussion Forum

A moving  coil galvnometer has 50 turns and each turn has an area 2 × 10^-4 m² .The magnetic field produced by the magnet inside the galvnometer is 0.02 T. The torsional constant of the suspension wire is 10^-4 N-m rad ^-1 . When a current flows through the galvanometer, a full scale deflection occurs, if the coil rotates by 0.2 rad. The resistance of the coil of the galvanometer is 50 Ω . This galvanometer is to be converted into an ammeter capable of measuring current in the range 0 - 10A , For this purpose , a shunt resistance is to be added in parallel to the galvanometer . The value of this shunt resistance in ohms, is................

Answer:

Explanation:

Given , N=50,

        A= 2 × 10^-4 m² , C=10 ^-4 , R= 50 Ω

              B= 0.02 T,  θ =0.2 rad

  N i_g AB= C θ

 $\Rightarrow$         $i_{g}=\frac{C\theta}{{N }{AB}}$

                       $i_{g}=\frac{10^{-4}\times 0.2}{50\times 2\times 10^{-4}\times0.02}=0.1A$

                       $V_{ab}=i_{g}\times G= (i - i_{g})S$

                       $V_{ab}=0.1\times 50= (1 - 0.1)\times S$

      5= 0.9 × S

              $S=\frac{50}{9}$Ω = 5.55 Ω