Question

State the principle of the step-down transformer and its working.

Answer 1

Principle: A transformer is based on the principle of electromagnetic mutual induction, i.e., whenever the amount of magnetic flux linked with a coil changes, an e.m.f. is induced in the neighboring coil.

Working

Alternating emf is supplied to the primary coil PP’. The resulting current induces a current in the secondary coil.

Magnetic flux linked with primary is also linked with the secondary. The induced emf in each turn of the secondary is equal to that induced in each turn of the primary.

Let

E_P − Alternating emf applied to primary

n_P − Number of turns in the primary

`(dphi)/dt-"Rate of change of flux through each turn of primary coil"`

`:.E_p=-n_p (dphi)/dt" ......(1)"`

E_s− Alternating emf of secondary

n_s − Number of turns in secondary

`:.E_s=-n_s (dphi)/dt" ....(2)"`

Dividing equation (2) by (1),

`E_s/E_p=n_s/n_p=k`

For step-up transformer, K > 1

∴ E_s > E_p

For step-down transformer, K < 1

∴ E_s < E_p