Levels

Lab

The physics

Magnetic flux measures how much field passes through a loop. θ is the angle between B and the loop's normal.

Φ = B A cos θ

A changing flux makes an emf. This is Faraday's law. With N turns, each turn adds its own emf.

ε = −N dΦ/dt

The flux can change in three ways. B can change. The area can change. The loop can turn.

While the flux changes, a current flows round the loop. The charge that flows depends only on the flux change. It does not depend on how fast the change happens.

q = N ΔΦ / R

Sliding a loop inside one uniform field makes no emf. Its flux stays the same.