The radius of a coil decreases at 10⁻² m/s in a uniform magnetic field B=10⁻³ Wb/m² perpendicular to the coil. If the radius is n/π cm when the induced emf is 1 µV, find n.
Physics · Electromagnetic Induction
JEE Mains

Question

The radius of a coil decreases at 10⁻² m/s in a uniform magnetic field B=10⁻³ Wb/m² perpendicular to the coil. If the radius is n/π cm when the induced emf is 1 µV, find n.

G1 Physics · Accepted Answer

For a circular coil, |ε|=2πBr|dr/dt|. Substituting ε=10⁻⁶ V, B=10⁻³ T and |dr/dt|=10⁻² m/s gives r=5/π cm, so n=5.