Faraday's Law of Electromagnetic Induction

Faraday's Law states that an EMF is induced only when there is a changing magnetic flux through a coil. The key word is changing.

The magnet is stationary inside the coil. A stationary magnet produces a constant (unchanging) magnetic field, so the magnetic flux through the coil is constant: $\Delta \Phi =0$.

Using $\mathcal{E}=N\frac{\Delta \Phi }{\Delta t}$, if $\Delta \Phi =0$, then $\mathcal{E}=0$. No EMF means no current, so the galvanometer reads zero.

The galvanometer reads zero because a static magnet produces no change in flux. The presence of a magnetic field alone is not enough — it must be changing.

The question tests whether students know that changing flux (not just the presence of a magnetic field) is required to induce a current.

This is incorrect. The strength of the magnetic field alone does not induce a current. A strong static magnet inside a coil induces nothing — only a changing field does.

This is also incorrect for the same reason. Flux passing through a coil is not sufficient; the flux must be changing to induce an EMF.

This gives the right answer (zero) but for the completely wrong reason. Resistance affects how much current flows given a voltage, but the fundamental reason here is that no EMF is induced at all.

'Zero, because there is no change in magnetic flux through the coil' is correct. It correctly identifies the cause (no change in flux) using Faraday's Law.

When a current flows through the primary coil, it creates a magnetic field. If that current is changing (switching on or off), the magnetic field through the secondary coil is also changing.

By Faraday's Law, $\mathcal{E}=N\frac{\Delta \Phi }{\Delta t}$. A changing flux ($\Delta \Phi \ne 0$) through the secondary coil induces an EMF, driving a brief current.

When the switch stays closed and current is steady, the magnetic field is constant → $\Delta \Phi =0$ → $\mathcal{E}=0$. No change means no induction.

The correct explanation is that the changing current in the primary creates a changing magnetic field, which by Faraday's Law induces an EMF in the secondary coil.

This question tests understanding of mutual induction and why steady current in the primary produces no effect in the secondary.

The two coils are electrically insulated from each other. Electrons do not transfer between them. Energy is transferred through the changing magnetic field, not by electron flow.

A steady current produces a constant magnetic field. Constant flux means zero rate of change, so by Faraday's Law, zero EMF is induced in the secondary.

Physical movement of a coil is one way to change flux, but it is not the only way. Here, the coils are stationary — induction occurs because the magnetic field itself is changing.

'The changing current in the primary creates a changing magnetic field, which induces an EMF in the secondary' correctly describes mutual induction using the principle of changing flux.