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Physics: 7. Sound
Please remember to photocopy 4 pages onto one sheet by going A3→A4 and using back to back on the
photocopier
Syllabus
OP40 Show that sound is a form of energy, and explain that sound is produced by vibrations
OP41 Show that sound transmission requires a medium and that echoes are reflected sound
OP42 Appreciate that the ear detects sound vibrations and that exposure to very loud sounds can cause
damage to hearing
OP43 Recall that the speed of sound is less than the speed of light
OP44 Explain the time lag between seeing and hearing the same event
Student Notes
To show that sound is a form of energy you must be able to show that it can do work (because energy is the
ability to do work). Work is done when an object is being moved. So we need to show that sound can move
something.
Demonstration
Hang a balloon in front of a speaker; note that when the speaker is turned on the balloon moves.
Demonstration
Feel the speaker vibrate by putting your hand on it. Notice that as the sound gets louder the vibrations get
bigger.
Demonstration
Notice that you can see and hear the bell ringing before the vacuum pump is
switched on.
After pumping the air out you can still see the bell ringing but can no longer
hear it.
Echoes occur when sound reflects from a surface back into your ears.
There are tiny hairs in your ear which vibrate when they detect sound and this then gets converted to
electrical signals which travel to the brain.
This is why people who work with loud machinery need to wear ear protectors.
Sound is a form of energy
Sound is produced by vibrations
Sound requires a medium
Echoes are reflected sound
The ear detects sound vibrations
Exposure to very loud sounds can cause damage to hearing
