Transformer

Transformers work by electromagnetic induction: a changing magnetic field in the primary coil induces a voltage in the secondary coil. The key word here is changing.

A direct current (DC) flows in one constant direction without reversing. This creates a steady, non-changing magnetic field around the primary coil.

Because the magnetic flux through the iron core is not changing, there is no electromagnetic induction in the secondary coil. No changing flux means no induced voltage.

The correct answer is: No voltage would be induced in the secondary coil. This is why transformers are designed exclusively for AC supplies.

The question asks what happens when a DC supply replaces the AC supply in a transformer. We need to think about what role AC plays in transformer operation.

The statement 'the transformer would still work because the voltage is the same' is incorrect. The type of current (AC vs DC) matters more than the voltage magnitude — transformers require alternating current.

'The secondary coil would produce a higher voltage than before' is wrong. There is no mechanism by which DC would produce a higher (or any) output voltage through electromagnetic induction.

'The iron core would melt due to increased current' is a distractor. While DC could cause heating in the coil resistance over time, this is not the primary effect and is not the standard physics explanation for why DC fails in a transformer.

The remaining correct answer is 'No voltage would be induced in the secondary coil' — DC produces a constant magnetic field, and a constant field cannot induce a voltage.

A transformer has three main components: the primary coil (input), the secondary coil (output), and the iron core that magnetically links both coils.

The soft iron core is specifically designed to carry (channel) the changing magnetic flux generated by the primary coil and direct it through the secondary coil. Soft iron is chosen because it magnetises and demagnetises rapidly.

The correct answer is the soft iron core. Without it, much of the magnetic flux would escape into the air and the transformer would be very inefficient.

The question asks which component channels the changing magnetic flux between the two coils of a transformer.

'The insulating layer around the wire' prevents electrical contact between turns — it does not channel magnetic flux.

'The secondary coil winding' is where the induced voltage appears — it receives the flux but does not channel it from one coil to the other.

'The connecting wires between the coils' do not exist in a transformer — the two coils are electrically isolated from each other and are not connected by wires.

By elimination, the correct answer is the soft iron core, which magnetically links the primary and secondary coils.