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 .