Identify the incorrect statement among the following:

The correct answer is Option (1) → The transformer works on the principle of self induction.

A transformer transfers ac power between two coils wound on a common iron core by mutual induction: the changing flux of the primary induces an emf in the secondary.

Option (1) The transformer works on the principle of self induction. — Incorrect statement. The emf in the secondary is caused by the changing current in the other (primary) coil, which is mutual induction, not self induction.

Option (2) When a.c. flows through a transformer, the material of the core of the transformer is magnetized and demagnetized repeatedly. — Correct statement. The alternating current reverses the magnetisation of the core every cycle, which causes the hysteresis loss.

Option (3) The core of the transformer is laminated to minimize the loss of energy due to eddy currents. — Correct statement. Thin insulated laminations increase the resistance to eddy currents and so reduce the heat loss.

Option (4) The transformer does not change the frequency of the current in secondary — Correct statement. The secondary emf follows the same changing flux, so it has the same frequency as the primary supply.

NCERT (2026-27):
Transformers – “… This is done with a device called transformer using the principle of mutual induction.”

Transformers – “… (iii) Eddy currents: The alternating magnetic flux induces eddy currents in the iron core and causes heating. The effect is reduced by using a laminated core. (iv) Hysteresis: The magnetisation of the core is repeatedly reversed by the alternating magnetic field.”