Mutual Induction Emf — the NEET Physics formula with its derivation, variables, validity constraints and worked solver.
Mutual Induction EMF Applies to a system of two magnetically coupled coils (primary and secondary) where the geometry and magnetic permeability of the core remain constant. Start with Faraday's Law of Induction: E = - d B dt . Define magnetic flux linkage in the secondary coil ( 2) as proportional to the current in the primary coil (I 1): 2 = M I 1. Differentiate the flux equation with respect to time: d 2 dt = M dI 1 dt (assuming M is constant). Substitute back into Faraday's Law to get E 2 = -M dI 1 dt . The mutual inductance M must be constant (linear media, fixed geometry). Quasi-static approximation is assumed. The flux linkage is proportional to the current. Confusing Mutual Inductance (M) with Self Inductance (L). Ignoring the negative sign which represents Lenz's Law (direction of induced EMF opposes the change in current). Thinking M depends on the current value, whereas it depends on geometry and core material. Assuming induced EMF exists when current is constant (dI/dt must be non-zero).