There
are two types of waves. These are known as longitudinal
and transverse waves. When a wave
travels, energy moves along a wave but there is no movement
of particles along the wave. Particles just move backwards and
forwards (longitudinal wave) or up and down (transverse wave)
about a fixed point. Think of a Mexican wave in a football stadium
- the spectators move up and down about a fixed point (their
seat) and the wave can be seen to travel around the stadium.
Longitudinal
Waves
Sound
is an example of a longitudinal wave. If you hit a metal bar,
the particles in the bar will vibrate backwards and forwards.
Longitudinal waves can be demonstrated by pushing and pulling
on a slinky spring. The spring stretches in places and squashes
in others. The wave travels along the spring as a series of
compressions (areas where it is squashed) and
rarefactions (areas where it is stretched).
Transverse
Waves
Waves
which form part of the electromagnetic spectrum (see
later) and water waves are examples of transverse waves.Transverse
waves can be demonstrated by moving a piece of rope up and down
(see diagram). In a transverse wave vibrations are at right
angles to the direction of movement.
Describing
Waves
You
should be able to label a transverse wave as shown in the diagram
below:
The
crest is the peak on the transverse wave
The
trough is the lowest part of a transverse
wave
The
amplitude is the maximum displacement of
the wave. This is half the crest to trough height as shown.
The
wavelength is the distance between two
crests or between two troughs
The
frequency of a wave is the number of crests
that pass through a point in one second
You
should also be able to label a wavelength, a compression and
a rarefaction on a longitudinal wave.
Calculations
on Waves
If you
are given any two of the following variables: the wave speed,
the frequency or the wavelength of a wave you should be able
to calculate the third. e.g. You should be able to calculate
a wave's speed if you know the frequency and the wavelength.
Learn the formula given below and practise rearranging it!
e.g.Calculate
the speed of a wave that has a frequency of 500 Hz and a wavelength
of 10 metres.
Wave
speed = frequency x wavelength
Wavespeed
= 500 Hz x 10m
Wavespeed
= 5000 m/s
For
waves which have the same speed:
The
frequency increases as the wavelength decreases
The
frequency decreases as the wavelength increases
For
waves which have the same frequency:
The wavelength
increases as the wave speed increases
The wavelength
decreases as the wave speed decreases.
Click on the link
below to try some questions on waves.
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2005 drparry.co.uk. All Rights Reserved.
