EM 5.8

1. AL Physics Moving Coil Galvanometer Turning torque (by I) = Resisting torque (by hairspring) EM 5.8

2. AL Physics Moving Coil Galvanometer ’  Concave magnet and small gap  ConstantRadial field B  magnetic force  coil plane (always)  Constant Torque i.e.  = BANI sin 90o = BANI Resisting torque due to the hairspring in which the restoring torque is directly proportional to the angle turned. i.e. ’ = k  where k is the torisonal constant (~ force constant)  is the angle turned At Equilibrium,  = ’ BANI = k   = (NBA / k) I •  I if N, B, A and c are constant  linear scale !! EM 5.8

3. AL Physics Moving Coil Galvanometer • Current Sensitivity =  / I = deflection per unit current •  / I = NBA / k • In order to increase the current sensitivity, • no. of turn of coils , • but the armature will be too bulky and the size of the air gap cannot be too small. • Magnetic field in the air gap , i.e. Stronger magnet is used and the air gap should be as narrow as possible. • area of the coil , • but the coils will swing about its deflected position. • Weaker hairspring, • but if the opposition of the suspension is too weak (reading again take time). EM 5.8

4. AL Physics D.C. Motor animation EM 5.8

5. AL Physics Practical D.C. Motor Concave magnet Smoother and Faster EM 5.8

6. AL Physics EXERCISE M.C. # 17, 18 5 minutes EM 5.8

7. AL Physics EM 5.8

8. AL Physics EM 5.8

9. AL Physics animation EM 5.8

10. AL Physics animation EM 5.8