This method involves using a signal generator is connected to a vibration
A longish piece of wire or string is fixed to the
vibration transducer and passed over a pulley wheel at the end of the
The other end of the wire/string is
connected to a hook system on which
you can add 'weights' to increase the tension on the wire/string.
You switch on the signal generator
and vibration transducer to set the
wire/string vibrating - the waves should oscillate up and down.
Adjust the frequency until you can get a
clear transverse standing wave (as in diagram B) and measure its
wavelength using the metre rule sighted behind the vibrating
Its easiest to measure the length
of as many half wavelengths as you can, calculate the average and
then double the average to get the full wavelength.
You can vary two things:
(i) Vary the weights added to
tension the string and measure the wavelength each time for a fixed
length of wire/string between the transducer and the pulley wheel.
(ii) Vary the length of the
wire/string between the transducer and the pulley wheel for a fixed
Obviously, you can do several
sets of results within the experimental framework of (i) and (ii).
For each set of experiments you
the frequency of the standing
wave (f in Hz)
the tension on the string/wire (T
the total length of the
wire/string (L in
the wavelength (λ
and you can calculate the speed
too (v = f x
λ in m/s).
This gives you loads of data
to play with!
You should find that the wavelength
of the string wire measured varies with:
(i) The in tension on the
wire/string for a fixed length.
You should find the frequency
increases and wavelength decreases the greater the tension on
The frequency is proportional
to the square root of the tension (f
Think of tightening the
tension on a guitar or violin string (fixed length) - the pitch
increases the more you tighten it up.
(ii) The length of the
wire/string for a fixed tension weight.
You should find that the
frequency increases and wavelength decreases the shorter the wire/string.
For a fixed tension weight,
the frequency of a stretched string is inversely proportional to
the length of the string (f
Having measured the wavelength
(convert to m), and knowing the frequency (Hz) from
the generator, you can then calculate the speed of the wave in each
speed = frequency x wavelength =
v = f x
λ = ? m/s
measuring the speed of sound in air