What is the name of the effect used by the moving-coil loudspeaker to produce sound waves? Explain how a moving-coil loudspeaker produces a sound wave - AQA - GCSE Physics - Question 8 - 2021 - Paper 1

A moving-coil loudspeaker operates by allowing an electric current to flow through a coil of wire situated in a magnetic field. This current creates a magnetic field around the coil, which interacts with the permanent magnet in the speaker.

As a result of this interaction, a resultant force is generated, causing the coil (and attached cone) to move. This movement of the coil back and forth produces compressions and rarefactions in the air, which we perceive as sound waves. When the direction of the electric current reverses, the direction of the force also reverses, enabling the coil and cone to move in the opposite direction, continuing to generate sound waves.

The results cannot be used to draw a valid conclusion because the student changed two variables at the same time: the number of turns on the coil and the frequency of the supply. When multiple variables are altered simultaneously, it becomes impossible to determine the individual effects of each variable on the loudness of the sound, thus confounding the results.