Understanding Electromagnetic Induction

Michael Faraday describes the discovery of electricity in 1831 without the use of a battery by using a magnet and a magnetic field. This process has since been termed electromagnetic induction and the setup is termed induced current. He worked on the apparatus which consisted of two coils of insulated wire A and B wound on a wooden core. The first coil was connected to a galvanometer while the second coil was connected to a battery source. When the battery was disconnected, the galvanometer was deflected, but when a soft iron core was used, a larger deflection was obtained. When the battery is connected firmly, no deflection was observed. The observation shows that the induced current flows only while a current change is made in the solenoid connected to the battery. When the battery is disconnected, a deflection in the galvanometer is obtained in the opposite direction.

An electromotive force can be induced in a straight conductor known as a magnetic field. When a conductor has moved a distance away from its normal position, it cuts across the field of the magnet, thereby, producing an induced current in the conductor perpendicularly to the magnetic field. Electromotive force (EMF) is only maximum at this current but minimum when parallel to the magnetic field.

Fleming's right hand rule is a mnemonic named after John Ambrose Fleming is applied when the current is induced in a single circuit and also useful in the case of generators and dynamos, the law states that;

"If your right hand is held so that the thumb, the fourth finger and the second finger or the middle finger are perpendicular to one another. The thumb represents the direction of motion in a conductor, the fourth finger represents the direction of the magnetic field while middle or the second finger represent the direction of the current ".

When the pole of a magnetic is brought closer to a solenoid connected to a center scale "O" or galvanometer, the galvanometer deflects to the right, showing that an induced current has been produced. When the magnet is stationary (at rest), the galvanometer reads "O" ; no current is found in the system (induced current not produced). But when the magnet is moved backward from the coil or solenoid, the deflection of the galvanometer is seen to be deflected in the direction of the magnet.

An induced current is produced only when there is a relative motion between the coil and the magnet. Therefore, the coil or solenoid can be moved instead of moving the magnet. It implies that:

• If the magnet moves toward the coil there will be changes in the number if lines linking the circuit thereby producing an induced current.
• The induced current depends on the strength of the magnet used.
• The induced current also depends on the number of turns of the coil wound around the solenoid; the higher the number of the coil, the greater or higher the induced current produced in the circuit.

1. 1
   Faraday's Law:

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   1. When there is a change in magnetic lines of force or flux, an induced current is produced in the circuit'.
   2. The induced electromotive force (EMF) or current in a circuit is produced as a result of the change in flux linking the coil.
   3. An induced electromotive force (EMF) or current in a circuit is directly proportional to the rate of change of magnetic flux or field line linking the circuits.

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2. 2
   Lenz's law

   :

    

   1. The induced current flows in such a direction as to oppose the motion producing it.
   2. This law is usually called Faraday's second law of electromagnetic induction and gives the direction of the induced current.

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3. 3
   Factors that determine the magnitude of induced current include

   :

    

   1. Strength.
   2. Number of turns of the coil.
   3. Distance between magnet and coil.
   4. Speed between the magnet and coil.
   5. Surface area of the coil.

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4. 4
   Application of Electromagnetic Induction includes

   :

    

   1. Transformer.
   2. Primary and Secondary coil.
   3. Induction coil.
   4. DC and AC generator.
   5. Dynamos.

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