Hello
How to make buzzer how inductor work in buzzer it generate ac when I solder led it light on both side no positive negative it on off does it make ac oscillator
A 'buzzer' is historically a mechanical device, consisting of an electromagnet and a normally closed switch contact. When power is applied the electromagnet pulls a spring loaded metal lever towards itself, operating the switch and disconnecting the power - the cycle then repeats. Just the same as an electric bell.
A buzzer without a coil is most likely a piezo disc, and an electronic oscillator feeding it.
It is the flyback or back EMF effect - when the supply is suddenly disconnected from an inductor, the current keeps flowing in the same direction until the magnetic field dissipates, and creates the opposite voltage across the inductor.
That is why a "flywheel diode" is normally used across DC solenoid and relay coils etc., it allows the current to circulate until the energy dissipates, without causing a high voltage pulse.
While the contact in the buzzer is closed, the voltage is the same as the supply; each time it opens, the reverse pulse happens.