Information is stored in audio/video tapes by magnetizing them. These tapes are actually long, thin plastic films coated with a magnetic material, mainly iron oxide.
Likewise, the player has a recording head which consists of a coil of a wire wound around a circular piece of iron with a small gap. Any current passing through the wire would produce a magnetic field around it.
Information (voice or image or any data) to be stored is converted into electric signals (by a microphone) amplified and fed to the recorder head. As the current varies in accordance with the image or sound (input signals) to be recorded, it produces a varying magnetic field.
When the tape is run through the small gap present in the recording head, the varying magnetic field magnetizes the particles on the tape rearranged their moments in accordance with the variation in the input signal.
To reproduce the signal recorded, the tape is again run past the recording/playing head which senses the magnetic field along the tape. This induces a varying current in the coil. This current is amplified and fed to the speaker or TV to reproduce the original message.
