MediumPhysicsHigh School (9–10)Electricity & Magnetism › Magnetic Effects of CurrentConceptualBoard Exam
Explain how a loudspeaker makes sound from a changing current…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
- Explain how a loudspeaker makes sound from a changing current.
- What happens to the sound when the current is larger?
- A cone moves to and fro times a second. How long does one to-and-fro take, in milliseconds?
Need a reminder? The key ideaShow
A galvanometer's coil turns in a magnet's field; its turn is proportional to the current. A loudspeaker's coil, fixed to a cone, moves to and fro with a changing current and makes sound. Both use the force on a current.
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. (a) The coil sits in the field of a permanent magnet and is fixed to a cone. The changing current makes a changing force, so the coil and the cone move to and fro. The cone makes the air vibrate: this is the sound.
Step 2. (b) A larger current gives a larger force and a larger movement, so a louder sound.
Step 3. (c) .
Answer: a changing force moves the cone; louder; .
Check. A faster to-and-fro gives a higher pitch.
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