A small flat search coil of area 5cm² with 140 closely wound turns is placed between the poles of a powerful magnet producing a magnetic field of 0.09T and then quickly removed out of the field region. Calculate (a) change of magnetic flux through the coil, and (b) emf induced in the coil.

Coil area = 5cm² = 5 × 10⁻⁴m²
Number of turns = 140
B = 0.09T = 9 × 10⁻²T
Magnetic flux = Φ = (BA) (number of turns)
= 9 × 10⁻² × 5 × 10⁻⁴ × 140
= 0.0063 = 6.3 × 10⁻³Wb
This is the initial flux. Final flux = 0.
ΔΦ = 6.3 × 10⁻³Wb
a) So ΔΦ = 6.3 × 10⁻³Wb
b) Now emf induced = ΔΦ/Δt
So we assume the coil is removed within a millisecond
So Δt = 1 × 10⁻³ second
So emf = 6.3 × 10⁻³/10⁻³ = 6.3 volts