SELF INDUCTION
When an AC current flows through a solenoid (an insulated copper wire wound in the shape of a spring) a magnetic field is produced around that wire due to the variation of current in AC ,the magnetic flux around that wire also changes .By Faraday's law of Electromagnetic induction Whenever there is a change in magnetic flux associated with a closed circuit an induced emf is produced on that wire. This phenomenon is called electromagnetic induction
What is the change in intensity of light of a lamp can be observed when a solenoid connected to AC?
Due to self induction an emf is produced in the solenoid.This emf always oppose the applied voltage. This emf is called back emf. Due to the back emf the applied voltage decreases .So the bulb glows dimmer.
What is the intensity of light observed if we place a iron core inside the solenoid in the above figure?
The intensity of light is very less. Because the strength of magnetic flux increases when we place a iron core inside the solenoid. So Back emf increases. So it oppose applied voltage . Then the applied voltage decreases
Can we done the same experiment using DC voltage?
No, Electro magnetic induction take place in AC current only
MUTUAL INDUCTION
We can produce an electric current in the second circuit utilizing the current of first circuit even if they are not in direct contact
Wind insulated copper wire( wire used for electric motor winding) at one end of a soft iron core and connect its ends to a cell. At the other end of the soft iron core wind another insulated copper wire. Connects its end to a Galvanometer .
OBSERVATIONS
When the switch is ON and OFF then we can observe a deflection in galvanometer If we keep the switch on for some time there is no deflection in galvanometer
EXPLANATION
When current flows through first coil magnetic flux is produced around that coil. The second coil is placed in the magnetic field of first one. When the magnetic flux around first coil changes then only an emf is induced on second coil. If we kept the switch on for a while there is no change in magnetic flux linked with second coil because it is DC current. So there is no deflection
When AC current is applied in fist coil. The magnetic flux produced around that wire continuously changes. The second coil is placed in that magnetic field so emf is continuously produced on second coil. This is the working principle of TRANSFORMER
TRANSFORMER
It is an electronic device to increase of decrease a given AC voltage. It works in the principle of mutual induction
There are two types of transformers STEP UP and STEP DOWN
STEP UP TRANSFORMER
Used to raise a low AC voltage to high AC voltage
Number of turns in secondary coil is greater than that of primary
Thick wire is used in primary coil and thin wire is used in secondary coil
STEP DOWN TRANSFORMER
Used to decrease high AC voltage to low AC voltage
Number of turns in primary coil is greater than that of secondary
Thick wire is used in secondary coil and thin wire is used in primary coil
If Np is number of turns in primary, Vp is voltage in primary. Ns is the number of turns in secondary, Vs is the voltage in secondary
Vs/Vp = Ns/Np
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