Galvanometer Deflection Law — the NEET Physics formula with its derivation, variables, validity constraints and worked solver.
Galvanometer Deflection Law This law applies when the magnetic torque acting on a current-carrying coil is balanced by the restoring torque provided by the suspension system, assuming uniform magnetic field and ideal conditions. Calculate the magnetic torque ( ( B )) acting on the coil: ( B = n B I A ). Calculate the restoring torque ( ( R )) due to the suspension system, which is proportional to the deflection angle: ( R = k ). Apply the condition for equilibrium (zero net torque): ( B = R ). Equate the two torques to obtain the deflection law: (n B I A = k ). The coil must be perpendicular to the magnetic field lines for maximum torque. The deflection angle must be small enough for the small-angle approximation to hold (sin ( ) )). Confusing the relationship between torque and deflection angle (it is proportional, not equal). Assuming the torque is proportional to the sine of the angle instead of the angle itself (small angle approximation). Forgetting that the magnetic torque depends on the area (A) and the number of turns (n).