Electromagnetic induction

what is meant by magnetic field

space in which magnetic force is experienced

what is a magnetic field line

a line showing direction of magnetic field

what is meant by self-induction

changing magnetic field produced by a coil induces a back emf in the coil itself

what is Faraday’s law

Faraday’s law states that the size of the induced emf is directly proportional to the rate of change of magnetic flux

explain the term electromagnetic induction

if a conductor is placed in a changing magnetic field, an emf appears in the conductor

describe an experiment to describe electromagnetic induction

Apparatus- Coil magnet,galvonameter

procedure- 1.set up apparatus as shown 2. move the magnet towards or away from the coil 3. the meter deflects indicating current or emf. 4, when the magnet is not moving the meter reads

conclusion- whenever the magnetic field passing through a coil is changing, an emf apperas in the coil. this is electromagnetic induction

define magnetic fux? SI Unit?

Φ = B.A Φ-MAGNETIC FLUX B-MAGNETIC flux density A-area Webber

in some modern seisometers, during an earthquake there is some relative motion between a magnet and a coil. explain why an emf is generated in the coil

because the magnetic field passing through the coil is changing

what is lenz’s law of electromagnetic induction

The induced current flows in such a direction as to oppose the change causing it

demonstrate Faraday’s law

Apparatus- galvonometer,coil, magnet

Procedure- 1.Move the magnet towards the coil slowly.the galvanometer gives a small deflection 2. Move the magnet towards the coil quickly.the galvanometer gives a larger deflection

Conclusion- The induced emf is proportional to the rate of change of flux through the coil

Demonstrate Lenz’s law

Apparatus- magnet,light aluminium ring,thread

Procedure- 1.Move the north pole of a bar magnet quickly towards it 2. the ring moves away from the approaching magnet 3. move the North pole quickly away from the ring and the ring follows the magnet

conclusion- as the north pole approaches the ring, current is induced in the ring, a North pole appears at the side of the ring nearest the magnet. the magnet repels it and the ring moves away.when the north pole is taken away from the ring the direction of the induced current changes causing a South pole to appear at the side of the ring facing the magnet. thus the ring is attracted to the magnet and follows it.

what is the difference between direct and alternating current

Alternating current reverses the direction in which it is flowing periodically

direct current always flows in the same direction

what is mutual induction

if a changing electric current in one circuit causes an induced emf to appear in a nearby circuit there is said to be mutual induction between the circuits

what is a transformer used for

to change the value of an a.c. voltage

draw a diagram showing the structure of a transformer

how is the transformer made more effective by laminating the core

electric currents induced in the core are significantly reduced. this reduces energy losses in the core

explain how a transformer works

the voltage V_i across the primary coil causes alternating current in the primary coil

this current causes an alternating magnetic flux in the iron core

this alternating flux passes through the seondary coil and induces an alternating emf V₀ in it

the size of the emf in the secondary ,V₀, depends on the number of turns i the secondary,N_s, and the number of turns on the primary coil N_p

why does a transformer not work with direct current

a steady direct current on the primary coil does not cause any change in magnetic field in the core of the transformer

the magnetic field passing through the secondary coil will not be changing. therefore electromagnetic induction will not take place and current will not be induced in the secondary coil