22. The Wave Equation
There are three measured
quantities in electromagnetic
waves:
The speed;
The wavelength;
The frequency.
23. What is the frequency of Radio 4 long wave
that broadcasts at a wavelength of 1500 m?
• c = fλ
We want the frequency so we must
rearrange:
f = c/λ
f = 3 × 108
m/s ÷ 1500 m = 200 000 Hz =
200 kHz
26. wave speed (m/s) = frequency (Hz) ×
wavelength (m)
v = f × λ
The strange looking symbol that looks like an upside-
down "y" is lambda, a Greek letter "l". It is the
physics code for wavelength. The other codes are:
c - wave speed (for electromagnetic waves c = 3 × 108
m/s)
f - frequency.
29. Wave Behaviour
What happens when…
• A wave meets a hard surface like a wall?
• A wave enters a new medium?
• A wave moves around an obstacle?
• A wave meets another wave?
37. Refraction
The bending of a wave as it
enters a new medium.
• It is caused by a change in
the speed of the wave as
it moves from one
medium to another
• Greater change in speed =
more bending of the wave
39. USES OF ELECTROMAGNETIC WAVES
Radio waves, microwaves,
infra red and visible light can
be used for communication.
40. USES OF ELECTROMAGNETIC WAVES
Communication signals may
be analogue (continuously
varying) or digital (only on
and off). Digital signals are
less prone to interference
than analogue and can be
processed by computers.
41. USES OF ELECTROMAGNETIC WAVES
Infra red and visible light can
be used to send signals along
optical fibres and so travel in
curved paths.
42. USES OF ELECTROMAGNETIC WAVES
Microwaves can pass
through the Earth’s
atmosphere and are used to
send information to and from
satellites and within mobile
phone networks.
43. Electromagnetic waves
gamma rays, X-rays, ultraviolet rays,
visible light, infra red rays, microwaves
and radio waves. Different wavelengths
of electromagnetic radiation are
reflected, absorbed or transmitted
differently by different substances and
types of surface.
45. Electromagnetic waves
Different wavelengths of electromagnetic
radiation have different effects on living
cells. Some radiations mostly pass
through soft tissue without being
absorbed, some produce heat, some may
cause cancerous changes and some may
kill cells. These effects depend on the type
of radiation and the size of the dose.
46. Electromagnetic waves
When radiation is absorbed the
energy it carries makes the
substance which absorbs it
hotter and may create an
alternating current with the
same frequency as the radiation
itself.
47. The Electromagnetic Spectrum
Light forms a small part of a large family of
electromagnetic waves. You will know how light splits
into the colours of the rainbow. The scientific term for
this is a spectrum.
You can see that the colours run into each other. There are no
distinct boundaries.
48. The rest of the electromagnetic spectrum is like
this as well. Here is a picture that sums up the
electromagnetic spectrum (em-spectrum).
49. Electromagnetic waves are like water waves. They
transfer energy from a source as waves. They have an
electrical component and a magnetic component, but
you don't need to know the details of them at this
stage.
All electromagnetic waves travel at the speed of light.
Speed of light (Physics code c) = 300 000 000 m/s = 3 ×
108
m/s
Features of Electromagnetic Waves
50. Electromagnetic waves travel in
straight lines.
Unlike other types of wave,
electromagnetic materials do not
need a material to travel through.
They travel in a vacuum, which is
why we see light from the Sun, but
don't hear its roar.
51. 1. Features of visible light waves.
2. Uses of gamma rays.
3. Uses of X-rays.
4. Uses of Ultraviolet rays.
5. Uses of Infra-red rays.
6. Uses of Microwaves rays.
7. Uses of Radio waves.
52. Features of visible light waves.
Light waves are a series
of changing magnetic
and electric fields where
the changes in a
magnetic field cause a
change in electric field
which causes another
electric field.
White light is a mixture
of all colours of the
visible spectrum.
It consists of waves of
different wavelengths
and frequencies all
travelling at the same
speed.
53. Uses of gamma rays
Gamma Rays are very high
energy waves released in
bursts from the nucleus of
certain atoms like Uranium
and Plutonium.
They are a form of nuclear
energy and are highly
radioactive.
Gamma rays are used to
destroy cancer cells which
are more sensitive to these
rays than normal cells.
54. Uses of X rays
X rays are produced when
fast moving electrons lose
energy suddenly e.g when
smashing into a metal
target.
Short wavelength X rays
penetrate dense metals
while long wavelength X
rays penetrate flesh but
not bone.
It is used to photograph
the inside of the body.
55. Uses of Microwaves
Microwaves are short
wave radio waves
generated by
vibrating electrons in
electrical devices.
They are easy to
direct through
ionosphere and hence
are used for satellite
communication and
mobile phones.
Food strongly absorb
microwaves,
converting their
energy into heat
energy in a
microwave oven.
56. Use of Ultraviolet waves
UV radiation received from
the sun is a good source of
vitamin D. However too
much exposure causes
damage to the skin
resulting in suntan to more
severe forms of skin
cancer.
UV is used to kill bacteria.
Some washing powders
have special chemicals
which absorb UV radiations
and then re-emit as visible
light to give the impression
the clothes are whiter.
57. Use of Infra red rays
These rays have frequency
below red light and give out
heat.
They are released from
vibrating atoms or molecules.
Hotter objects release more
infrared rays.
Remote control devices emit
infrared rays which are
detected by special
components of TV. They are
then converted to electrical
energy to control functions
58. Use of Radio Waves
Radio waves
Amplitude modulation Frequency modulation.
Radio waves are
generated by oscillating
electrons e.g in a
transmitting aerial.
Long radio waves are
useful for
communicating around
the Earth as they diffract
along the Earth’s surface.
Short radio waves travel
through ionosphere.
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owner. No copyright infringement intended.
