Electromagnetic Induction

Card # 69‐Electromagnetic Induction: It is a phenomenon of production of electric field with the help of varying magnetic field. Whenever there is a relative motion between a coil and a magnet an emf is established in the coil called the induced emf. If the coil is closed a current flows in it, this current is called induced current and phenomenon is called electromagnetic induction. Magnetic Flux: The no. of magnetic line of force passing normally through any area in a magnetic field is called magnetic flux linked with that area. It is denoted by Ф. Ф=BA=FA IL Its unit is Weber. Faraday’s law: 1) Whenever there is a change of magnetic flux through a circuit, there will be an induced emf and this will last as long as the change persists. 2) The magnitude of the induced emf is equal to the time rate of change of magnetic flux. ε = - dφB/ dt Negative sign indicates that the induced emf ε opposes the change of flux. ε = -N dφB dt

Lenz’s Law: The direction of induced current is such that it opposes the change or cause which produced it. This law is used to find out the direction of current.

Self Induction: Whenever the electric current passing through a coil or a circuit changes the magnetic flux link with it is also change. As a result an emf is induced in the coil which opposes the change that causes it. It is called self induction of electricity. Mathematical expression: Magnetic flux in coil α current in coil ΦαL Φ = LI dФ = -L dI dt dt ε = -L dI (from faraday’s law) dt

Mutual Induction: Whenever the current passing through a coil or circuit changes the magnetic flux linked with a neighboring coil or circuit will also change. Hence emf will be induced in the neighboring coil. This phenomenon is called mutual induction. Magnetic flux in secondary coil α current in primary coil Фs α IP Фs α MIP