A galvanometer of resistance 80 ohm ,shunted by a resistance 20 ohm is joined in series with a resistance 200 ohm and a cell 1.5V . what is the sensitivityof the galvanometer if it shows a deflection of 30 divisions .

Dear Student,

Sensitivity = Deflection / current passed through Galvanometer
Given Deflection = 30
to find current through galvanometer
Net Resistance = 20 ohm || 80 ohm series 200 ohm
                       = 216 ohms
Net current from battery = V/net resistance
                                     = 1.5 / 216 
                                    = 0.00694 amp
Current through galvaometer :
by current divider formulae I = 20/ (20+80)   * ​0.00694 amp   = 0.001388 amp

Sensitivity = Deflection / current passed through Galvanometer
                 = 30 / ​0.001388 = 21739.13                                  
If u consider galvanometer to be together with the shunted part 

Sensitivity = Deflection / current passed through Galvanometer
                 = 30 / ​ 0.00694 = 4322.76