A closed circuit with a light bulb is introduced into the steel core of a transformer connected

A closed circuit with a light bulb is introduced into the steel core of a transformer connected to a voltage of 220V. Why does the light come on at the same time?

If the transformer is connected to voltage, then this means that an alternating current flows through its winding. This current induces an alternating magnetic flux in the transformer core. By introducing a closed circuit with a light bulb into the steel core of the transformer, we will achieve the fact that the alternating magnetic flux of this core will pass through the circuit. According to the law of electromagnetic induction, an electric current will arise in such a circuit, the flow of which will cause the light bulb to glow.