What are the three wires going to the needle on a stereo record player?

Answer:

Answer

The three wires that connect to the needle holder or cartridge are the left and right channels, and ground. Colors vary, but red is usually right side, white is left side, and black is common (ground). Some cartridges have additional grounds or a neutral. The needle picks up vibrations from the analog signals in the two sides of the groove on the record. The cartridge converts these vibrations into a faint electrical signal. A preamplifier increases (amplifies) the signals to a higher voltage level that is then used to drive the main amplifier. The main amplifier drives the magnetic coils in the speakers, which convert the analog electrical signal back into sound waves.
All of which are called Transducers. A transducer is a device that converts one type of energy to another. The conversion can be to/from electrical, electro-mechanical, electromagnetic, photonic, photovoltaic, or any other form of energy. While the term transducer commonly implies use as a sensor/detector, any device which converts energy can be considered as a transducer.