Electricity from Magnetism

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Science > Physics > Magnetic Effect of Electric CurrentYou are Here
  • Michael Faraday worked on this field to produce electricity from magnetism. This effect is known as electromagnetic induction. Fraday proposed the laws of electromagnetic induction.

Faradays Coil and Magnet Experiment for Demonstration of Electromagnetic Induction:

Electromagnetic Induction 01

  • A coil of insulated copper wire is connected to a centre zero galvanometer. A bar magnet is held near the coil. Initially, the galvanometer shows zero deflection.
  • When the magnet is moved towards the coil, a momentary deflection is observed towards one side. When the magnet comes to rest, the deflection also becomes zero. If the speed of motion of the magnet is increased, the deflection also increased.
  • When the magnet is moved away from the coil, a momentary deflection is observed in the opposite direction. This direction is also observed as long as the magnet is in motion.
  • The same result is obtained by keeping magnet stationary and coil moving towards or away from the magnet.
  • Thus we can conclude that as long as there is a relative motion between the closed coil and the magnet, a current is induced in the coil. This phenomenon is known as electromagnetic induction.
  • The strength of induced current can be increased by increasing the number of turns of the coil, strength of magnetic field and the relative speed between the coil and the magnet.
  • By some mechanical means if we are able to maintain the relative motion between the coil and the magnet we can produce induce electric current continuously. This is the principle of the electric generator.
  • In electric generator actually, the coil is rotated in the fixed magnetic field.
  • As the magnet is moving continuously to and fro, the direction of induced current is continuously changing. Hence it is termed as alternating current (A.C.). The electric supply we get at our home or in the industry is A.C.

Dynamo or Electric Generator (application of Electromagnetic Induction):

  • A dynamo is a device that produces electrical energy from a mechanical energy source. The process is known as electricity generation.

Principle:

  • When armature coil is rotated in a magnetic field, the number of magnetic lines passing through the coil change due to which electricity is produced.

Construction:

  • The armature coil ABCD is a rectangular wooden frame on which a coil of insulated copper wire is wound. The coil is capable of rotating between the poles of strong horseshoe magnet by some mechanical mean. The ends D and A of the coil ABCD are connected to the metallic rings R1 and R2 respectively. Carbon brushes B1 and B2 are in contact with the rings R1 and R2 respectively. The rings R1 and R2 rotate with the axle rotating the coil. The brushes B1 and B2 do not rotate.  The ends of brushes B1 and B2 are connected to the external circuit to which electricity is to be supplied.

Working:

  • The horseshoe magnet produces uniform magnetic field. Due to rotation magnetic flux linked with the coil changes contnuously and induced current is produced. This induced current is used to run the external circuit.

Uses:

  • It is used to produce electricity as the alternate source of electric supply.

Transformer (application of Electromagnetic Induction):

  • The transformer is a device which converts the alternating voltage from one value to another. It works on the principle of mutual induction.

Construction:

  • A transformer consists of two sets of a coil, primary coil and secondary coil, which are well insulated from each other. The primary coil is input coil and the secondary coil is output coil. The two coils are wound on a soft iron core either one above other or on the separate arm. The soft iron core is formed by laying one above the other thin insulated strips made up of soft iron.
  • There are two connections. The coil which is connected to the source of an A.C. supply is called the primary of the transformer, while another coil is connected to the output source, this coil is called the secondary coil of the transformer.

Working:



  • When an alternating source of voltage is applied across the primary. it creates a changing magnetic flux which is linked to the secondary coil. The value of the flux linked with the coils depends on the number of turns of both the coils. Due to changing magnetic flux linked with secondary coil an induced current is produced in it.

Types of Transformers:

  • Depending upon the ratio of output voltage to the input voltage, transformers are classified into two types.

Step up transformer:

  • When the output voltage is greater than the input voltage (VS > VP or NS > NP), the transformer is called as a step-up transformer.

Step down transformer:

  • When the output voltage is less than the input voltage (VS < VP or NS < NP), the transformer is called as a step-down transformer.

Whrere V= output voltage at secondary

V= Input voltage at primary

N= Number of turns of the secondary coil

N= Number of turns of the primary coil



Electric Motor (application of Electromagnetic Induction) :

  • It converts electrical energy into mechanical energy.

Principle:

  • When current carrying conductor is placed in a magnetic field then it experiences a force.

Construction:

  • The armature coil ABCD is a rectangular wooden frame on which a coil of insulated copper wire is wound. The coil is capable of rotating between the poles of strong horseshoe magnet by some mechanical mean. The ends D and A of the coil ABCD are connected to the metallic rings R1 and R2 respectively. Carbon brushes B1 and B2 are in contact with the rings R1 and R2 respectively. The rings R1 and R2 rotate with the axle rotating the coil. The brushes B1 and B2 do not rotate.  The ends of brushes B1 and B2 are connected to the source of electricity.
  • When current is passed through coil ABCD it experiences continuous force on its arms AB and CD. These forces are equal, opposite and their lines of action are different. They form a couple. Under the action of the torque produced by the couple, the coil starts rotating. The coil is fitted with the rotor shaft.
  • Construction wise the A.C. generator and motors are similar. The difference is that in generator coil is rotated mechanically (by supplying mechanical energy) and electricity is generated while in the motor, electricity is supplied and mechanical work is obtained.

Uses: 

  • Electric motors are used in electric cars, rolling mills, electric cranes, lifts, drilling machine, fan, hair dryers, blowers, refrigerators, washing machine, mixers, blenders, etc.
Science > Physics > Magnetic Effect of Electric CurrentYou are Here
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