A rod moves at an angle θ with the direction of magnetic field, velocity E = – Blv sin θ. An emf is induced( i) When a magnet is moved with respect to a coil.( ii) When a conductor falls freely in East-West direction.( iii) When an aeroplane flies horizontally.
( iv) When strength of current flowing in a coil is increased or decreased, induced current is developed in the coil in same or opposite direction.
( v) When a train moves horizontally in any direction.
Fleming’ s Right Hand Rule
If we stretch the thumb, the forefinger and the central finger of right hand in such a way that all three are perpendicular to each other, th. if thumb represent the direction of motion, the forefinger represent tile direction of magnetic field, then centra } finger will represent the direction of induced current.
If R is the electrical resistance of the circuit, then induced current in the circuit is given by I = E / R
If induced current is produced in a coil rotated in uniform magnetic field, then I = NBA ω sin ωt / R = I o sin ωt where, I o = NBA ω = peak value of induced current, N = number of turns in the coil, B = magnetic induction, ω = angular velocity of rotation and A = area of cross-section of the coil.
Eddy Currents
If a piece of metal is placed in a varying magnetic field or rotated high speed in a uniform magnetic field, then induced current set up the piece are like whire pool of air, called eddy currents.
The magnitude 0f eddy currents is given by i = – e / R = dφ / dt / R, where R is the resistance.