Magnetic pickup cartridge of a record player. The cartridge holds the stylus or needle (not seen), which transforms the grooves in a record (black, lower centre) into sound. In a moving magnet cartridge (seen here), the stylus carries a tiny, permanent magnet placed between a series of fixed coils. The magnet moves in response to grooves in a record, which induces a current in the coils. The current is then fed to an amplifier and sound is produced.