AQA · GCSE · Physics
Course version: 8463 · Version from Sept 2016
Students should be able to explain how a moving-coil loudspeaker and…
Full specification wording
Loudspeakers (physics only) (HT only): Students should be able to explain how a moving-coil loudspeaker and headphones work.
Questions on this show a cross-section: a cylindrical magnet with the coil sitting in the narrow gap between its north and south poles, the coil fixed to the narrow end of a paper cone, and the…
Checked against the AQA 8463 specification (opens in a new tab) on .
- Point 2 of 2
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
Questions on this show a cross-section: a cylindrical magnet with the coil sitting in the narrow gap between its north and south poles, the coil fixed to the narrow end of a paper cone, and the cone held at its rim by a flexible surround. Reading that diagram is half the answer. The field in the gap runs across the coil, so the force on the coil acts along the axis of the cone, in or out, and the flexible surround lets the coil and cone move freely and spring back. Headphones are the same device made small: a light coil and a thin diaphragm instead of a large cone, driven by a much smaller current, which is why they can be run straight from a phone. In both, the frequency of the sound matches the frequency of the current, and the amplitude of the movement sets the loudness.
What earns the marks
- Identifying the coil sitting in the gap between the poles of the permanent magnet.
- The force on the coil acting along the axis, in or out, so the coil moves rather than turns.
- The cone or diaphragm being attached to the coil and moving with it.
- Linking the frequency of the current to the frequency of the sound produced.
- Linking the size of the current to the amplitude of the vibration and so to the loudness.
Common mistakes and how to put them right
Labelling the cone as the part that carries the current, when it is the coil.
Saying the coil rotates like a motor coil, when the arrangement of the field makes it move in and out.
Treating headphones as a different mechanism rather than a small moving-coil loudspeaker.
Leaving the permanent magnet out of the explanation, so there is no field for the current to interact with.
Exam tips
- Label the coil, magnet, cone and surround on the given figure, then use those labels in your sentences.
- Mention one thing that changes the loudness and one that changes the pitch; questions often ask for both.
- A steady direct current holds the cone in one position and makes no sound; say so if you are asked.
Try the lesson
The start of the Loudspeakers (physics only) (HT only): Students should be able to explain how a moving-coil loudspeaker and headphones work. lesson, made from checked teaching notes for this specification point.
Have a go first
In a moving-coil loudspeaker, what is the direction of the force on the coil when a current flows through it in a magnetic field?
Listen
Questions on this show a cross-section: a cylindrical magnet with the coil sitting in the narrow gap between its north and south poles, the coil fixed to the narrow end of a paper cone, and the cone held at its rim by a flexible surround. Reading that diagram is half the answer. The field in the gap runs across the coil, so the force on the coil acts along the axis of the cone, in or out, and the flexible surround lets the coil and cone move freely and spring back. Headphones are the same device made small: a light coil and a thin diaphragm instead of a large cone, driven by a much smaller current, which is why they can be run straight from a phone. In both, the frequency of the sound matches the frequency of the current, and the amplitude of the movement sets the loudness. A strong answer earns marks for these points. identifying the coil sitting in the gap between the poles of the permanent magnet. the force on the coil acting along the axis, in or out, so the coil moves rather than turns. the cone or diaphragm being attached to the coil and moving with it. linking the frequency of the current to the frequency of the sound produced. Exam tip: Label the coil, magnet, cone and surround on the given figure, then use those labels in your sentences.
Key words
Say what each word means before you turn the card.
moving-coil loudspeaker
Try answering aloud or in your head before turning the card.
field across the gap
Try answering aloud or in your head before turning the card.
cone and diaphragm
Try answering aloud or in your head before turning the card.
amplitude and frequency
Try answering aloud or in your head before turning the card.
See every definition
- moving-coil loudspeaker
- A device in which a coil sits in the narrow gap between the poles of a cylindrical magnet, fixed to the narrow end of a paper cone held at its rim by a flexible surround.
- field across the gap
- The field in the gap runs across the coil, so the force on the coil acts along the axis of the cone, in or out.
- cone and diaphragm
- The cone or diaphragm is attached to the coil and moves with it, and the flexible surround lets the coil and cone move freely and spring back.
- amplitude and frequency
- The frequency of the sound matches the frequency of the current, and the amplitude of the movement sets the loudness.
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