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Consider two coils of wire kept side by side. When the strength or direction of the current in, , one coil changes, the magnetic flux around it changes. As a result, an emf is induced in the, secondary coil. This phenomenon is the mutual induction,, , > The coil into which we give current for the production of magnetic field — Primary coil, , (input coil), > The coil in which induced emf is generated - Secondary coil (output coil), , Transformer is a device for increasing or decreasing the voltage of an AC without any, change in the electric power., , > Transformer which increases AC voltage - step up transformer,, > Transformer which decreases AC voltage -step down transformer., , When AC is given to the primary coil of a transformer, a varying magnetic field is produced, around it. As a result an emf is induced on the secondary coil, which is situated on the same, magnetic field. The emf induced on the secondary coil is proportional to the number of turns on it., , > Working principle — Mutual Induction (Electromagnetic induction), , , , , , Secondary, , coll Secondary, , Primary, coil, , coil, , , , , , inding, , induy, inding,, , , , , , , , , , , , , , step up transformer step down transformer ee, HSSLIVE.IN 8/18 ss, Step up transformer Step down transformer, Number of turns in the primary coil is lesser Number of turns in the primary coil is greater, than Secondary coil than Secondary coil., Output voltage is greater than input voltage. Input voltage is greater than output voltage., Thickness of primary coil is greater than Thickness of secondary coil is greater than, secondary coil, primary coil,, Input current is greater than output current. Output current is greater than input current., , , , , , , , , , The change in magnetic flux due to the flow of an AC in a solenoid will generate a back, emf in the same solenoid in a direction opposite to that applied to it, This phenomenon is known as, , the self induction,, , > Due to self induction, the effective voltage in the circuit is decreases. Hence the intensity of, bulb in the circuit is also decreases., , For self induction,, > Supply current must be AC,, > Asolenoid must be included in the circuit.