Ask each child to complete the table (which can also be
downloaded as a worksheet from the Science in School
websitew4), recording whether they experience each sound
as being very loud, loud, medium loud, quiet or very quiet.
This can be a little tricky. To make it easier, start with 16 000
Hz and do pairwise comparisons between neighbouring frequencies
to be measured, i.e. ‘How do you perceive the
sound at 16 000 Hz? Now listen to the sound at 8000 Hz –
how do you perceive it in comparison?’ And so on.
Typically, the human ear is most sensitive to the frequencies
at which we usually speak (about 200–3500 Hz).
With the help of a secondary-school mentor (or teacher),
each child should plot the perceived volume (e.g. loud = 8)
against the frequency of the sound.
It is useful to make the same measurements with adults (e.g.
teachers or parents) as well, because as we age, we hear
high-pitched sounds less well. You may notice this when the
TV is on – young children may hear a high-pitched whistling
noise whereas adults do not.
How does sound reach the ear? The swinging
candle
Because sounds are transported by variations in air pressure,
sound moves air particles. The movement of a candle flame
is used to illustrate this. Sound with a low frequency can
even blow out a candle flame.
Materials
· A CD player with a bass loudspeaker playing
techno music
· A candle and matches
· A paper funnel
· A (bass) drum with a hole in the back
· A signal generator with amplifier
· A loudspeaker suitable for low frequencies
(at least as low as 100 Hz)
· Cables
Procedure
1. Place a burning candle in front of a CD player with a bass
loudspeaker playing techno music. The flame will flicker
in time with the music. If the effect is not very visible, use
a paper funnel between the loudspeaker and the candle
to enhance it.
2. Place the burning candle in front of the hole at the back
of a drum. Beat the drum on the other side and watch the
flame move or be blown out.
3. Using the cables, connect the loudspeaker to the signal
generator and turn it to a low frequency (100 Hz). The
candle will be blown out. To enhance the effect, you can
use a paper funnel between the loudspeaker and the candle.
What happens in the ear?
Use a plastic or paper model (which may be homemade) of
the ear to illustrate the different parts of the ear, which will
be explained in the following experiments.