Electromagnetic induction, the phenomenon where a changing magnetic field induces a voltage in a nearby conductor, has numerous practical applications. Some applications of electromagnetic induction include electric generators, transformers, induction cooking, and magnetic flow meters.
applications of electromagnetic induction: induction coil
Induction coil is an important application of the electromagnetic induction. The induction coil consists of few turns of thick insulated copper wire wound on a primary coil. Then a secondary coil of many turns of thin insulated copper wire. we wound Both primary and secondary coil on a soft iron core. see the figure below:
The structure and working of the induction coil
we connect the primary coil to a direct current source of low voltage. In the figure below , we have wound the primary and secondary coil on top of the other.
When we close the switch , the soft iron core becomes magnetised due to the current in the primary coil. This causes it to attract the soft iron armature. The moving armature armature opens the contacts and cuts off the primary current, rapidly reducing the magnetic field to zero. This induces a large a large e.m.f in the secondary coil by mutual induction. However, the spring pulls the armature back to its initial position. This action completes the circuit again in the primary circuit so that the current flow again. This process repeats itself.
The switching on and off of the primary coil is thus continuous hence continuous changing magnetic flux. The induced e.m.f in the secondary coil is much higher when the primary coil is switching off than when switching it on. Remember the rate of current decay is usually higher than the rate of current build up in electromagnetic induction.
Many secondary coil increases the magnitude of the induced e.m.f in the secondary coil.Spark then jumps across the gap G between the two ends of the secondary coil. Hence can be used to ignite petrol-air mixture in a car engine.
Sparks may also occur at the contacts due to magnetic field of the primary coil. This cuts the primary coil fulfilling the Lenz’s law to keep primary current flowing.
A capacitor connected across the contacts minimizes the sparking. This causes the primary current and hence the magnetic flux to decay smoothly to zero.
some applications of electromagnetic induction: The moving-coil Microphone
The moving-coil microphone is a popular application of the electromagnetic induction. A coil of wire is wound on a cylindrical former connected to a diaphragm and placed between the poles of a magnet. see the diagram below:
Sound waves from a source sets the diaphragm in vibration. Figure below shows a typical wave profile :
This way, it causes the coil to move to and fro, cutting the magnetic field. The field is radial so that the motion is perpendicular to it for maximum flux linkage. An induced e.m.f of varying magnitude sets up varying current in the coil. An amplifier is used to increase the amplitude of this current before it is fed into a loudspeaker. In the loudspeaker, it is converted back to sound.