|Class 12 Physics Electromagnetic Induction||Faradays laws of Induction|
Faraday’s laws of Induction
First law: -
Second law: -
Problem:- A circular coil of radius 10 cm, 500 turns and resistance 2 Ω is placedwith its plane perpendicular to the horizontal component of the earth’smagnetic field. It is rotated about its vertical diameter through 180°in 0.25 s. Estimate the magnitudes of the emf and current induced inthe coil. Horizontal component of the earth’s magnetic field at theplace is 3.0 × 10–5 T.
Initial flux through the coil,
ΦB (initial) = BA cos θ
= 3.0 × 10–5 × (π ×10–2) × cos 0º
= 3π × 10–7 Wb
Final flux after the rotation,
ΦB (final) = 3.0 × 10–5 × (π ×10–2) × cos 180°
= –3π × 10–7 Wb
Therefore, estimated value of the induced emf is,
ε = N (ΔΦ/Δt)
= 500 × (6π × 10–7)/0.25
= 3.8 × 10–3 V
I = ε/R = 1.9 × 10–3 A
Note that the magnitudes of ε and I are the estimated values. Theirinstantaneous values are different and depend upon the speed ofrotation at the particular instant.
Problem:- A small piece of metal wire is dragged across the gap between the pole pieces of a magnet in 0.5s.The magnetic flux between the pole pieces is known to be 8x10-4 Wb. Estimate the emf induced in the wire?
dΦ = 8x10-4 Wb
e= - (dΦ/dt) =- (8x10-4) / (0.5)