Question

Why does a buzzer starts to buzz as soon as the circuit is complete?

Answer 1

Depending on the distance between the electromagnet and the nail, the rigidity of the rubber band and the strength of the electromagnet, the circuit can be broken and completed several times a second. Hence you hear a buzzing sound.

Answer 2

The circuit is complete again and the the electric charges start to flow. ... Depending on the distance between the electromagnet and the nail, the rigidity of the rubber band and the strength of the electromagnet, the circuit can be broken and completed several times a second. Hence you hear a buzzing sound