P1.5.1 |
General properties of waves |
a) Waves transfer energy. |
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b) Waves may be either transverse or longitudinal.
Candidates should understand that:
In a transverse wave the oscillations are perpendicular to the direction of energy transfer.
In a longitudinal wave the oscillations are parallel to the direction of energy transfer. |
The syllabus gives you the definitions that they expect you to quote for these waves - learn them! |
c) Electromagnetic waves are transverse,
sound waves are longitudinal and
mechanical waves may be either transverse or longitudinal. |
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d) All types of electromagnetic waves travel at the same speed through a vacuum (space). |
That speed is 3.0 x 108 m/s. This is the fastest possible speed! |
e) Electromagnetic waves form a continuous spectrum.
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Candidates should know the order of electromagnetic waves within the spectrum, in terms of energy, frequency and wavelength.
Candidates should appreciate that the wavelengths vary from about 10–15 metres to more than 104 metres. |
f) Longitudinal waves show areas of compression and rarefaction. |
Compression is where particles are closer together... rarefaction is where the particles space out more. Try to use the scientific words correctly in your answers to explain what longitudinal waves are! |
g) Waves can be:
 reflected,
refracted and
diffracted. |
Candidates should appreciate that significant diffraction only occurs when the wavelength of the wave is of the same order of magnitude as the size of the gap or obstacle. |
h) Waves undergo a change of direction when they
are refracted at an interface. |
Waves are not refracted if travelling along the normal. Snell's law and the reason why waves are refracted are not required. |
i) The terms
frequency,
wavelength and
amplitude. |
You are expected to define these - see this page for the wave definitions you should know. |
j) All waves obey the wave equation:
v = f x λ |
v is speed in metres per second, m/s
f is frequency in hertz, Hz
λ is wavelength in metres, m
Candidates are not required to recall the value of the speed of electromagnetic waves through a vacuum. |
| k) Radio waves, microwaves, infrared and visible light can be used for communication. |
Candidates will be expected to be familiar with situations in which such waves are typically used and any associated hazards, eg:
■ radio waves – television, and radio (including diffraction effects)
■ microwaves – mobile phones and satellite television
■ infrared – remote controls
■ visible light – photography. |
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