An air-cored solenoid of length 30 cm, cross-sectional area 25 cm² and 500 turns carries 2.5 A. The current is switched off in 10⁻³ s. Find the average back emf across the open switch, neglecting end effects.
Physics · Electromagnetic Induction
JEE Advanced

Question

An air-cored solenoid of length 30 cm, cross-sectional area 25 cm² and 500 turns carries 2.5 A. The current is switched off in 10⁻³ s. Find the average back emf across the open switch, neglecting end effects.

Physics · Electromagnetic Induction

G1 Physics · Accepted Answer

Use εₗ=−L(dI/dt), U=½LI², and for mutual induction ε₂=−M(dI₁/dt). Applying the stated geometry/circuit condition gives 6.5.