A transformer is a static device that transfers electrical energy from one circuit to another through inductively coupled conductors the transformer's coils. A varying current in the first or primary winding creates a varying magnetic flux in the transformer's core, and thus a varying magnetic field through the secondary winding. This varying magnetic field induces a varying electromotive force (EMF) or "voltage" in the secondary winding. This effect is called mutual induction.
Why to use a transformer?
In long-distance electrical transmission, there is a chance for energy loss, to compensate the energy source transformer are used to increase the energy at constant distant points. To reduce the transmission losses electric current is transmitted in high energy from the power plants.This high voltage should be decreased for household uses.
To increase the voltage we use step-up transformers and to decrease voltage step-down transformers are used.
The principle of transformer is mutual induction. The principle of mutual induction state that when two coils are inductively coupled and if the current in the coil change uniformly then the emf induced in the other coils. The emf can drive a current when a closed path is provided to it.
When an alternating current flow in the primary winding coils, a changing magnetic flux is generated in the around the primary coil.
The changing magnetic flux is transferred to the secondary through the iron core. The changing magnetic flux is cut by the secondary coil, hence induces an emf in the secondary coil. The load connected to the secondary coil drives the induced current.
If the number of windings in the secondary coil is more than the primary coil, then the transformer is step-up transformer and if the primary coil has higher number coils then it is step-down.
In transmission AC power supply
Audio transformers for couple amplifier
Transformers are used in old televisions.