1. Waves X-rays are used in hospitals to take radiographs.
X-rays and gamma rays damage living tissue when they pass through it.
Large doses can kill cells, small doses can cause cancer
Gamma rays
Have the shortest wavelengths
used to kill bacteria in food, sterilise surgical equipment and kill cancer cells.
Microwaves
Short waves
Can pass through atmosphere for satellite communications
Used in cooking, microwave ovens - heat water molecules
Infrared-IR
All objects emit IR. The hotter the object the more IR it emits
IR heat objects.
Uses: heaters, IR scanners, IR cameras, remote controls, optical fibres and communications
X-rays and gamma rays are absorbed by dense material such as bone and metal but pass through soft tissue
Radio waves
Have the longest wavelengths
Used in communications
Radio waves - smallest long waves - 300,000Hz+
Carry radio, TV, mobile phone signals
Alternating voltage  ariel  receiver
Frequency of radio wave = alternating voltage of carrier wave
High frequency radio waves-
Carry more information
Have a shorter range
Less diffraction
Optical Fibres
Visible light and IR carry signals
Carry more info than wires
More secure, signal stays in wire
Analogue signals vary continuously in amplitude or frequency
Digital signals are on or off. Digital signal free of interference and carry more information.
Carrier waves (radio, microwaves etc) carries digital/analogue signal
Radio waves are reflected by the IONOSPHERE.
Stronger in summer
Waves
Ultraviolet-UV
Found naturally in sunlight.
UV harms the skin and
eyes, causes a sun tan, used in security markers
The use of radio waves depends on the frequency of the waves
All EM waves travel through space at speed of light (300 million m/s).
Wave speed= Frequency X Wavelength
(m/s) (Hz) (m)

2. Waves Properties Law of reflection Angle of = angle of
Incidence reflection
Waves going from a dense medium to a less dense medium speed up at the boundary. This causes light rays to bend when they pass from glass to air at an angle other than 90º. This is refraction.
Beyond a certain angle, called the critical angle, all the waves reflect back into the glass. We say that they are totally internally reflected.
When light passes from a more dense to a less dense substance, (for example passing from water into air), the light is refracted (or bent) away from the normal.
When light passes from a less dense to a more dense substance, (for example passing from air into water), the light is refracted (or bent) towards the normal.
Waves Properties
The Earths atmosphere absorbs all electromagnetic waves, except visible light, radio waves and some UV radiation.
Satellite detectors are used to make observations outside the visible and radio spectrum.
Clear images are observed using telescopes on satellites detecting visible light.
Big Bang (BB)Theory
Massive explosion from a small point
Background microwave radiation is radiation created just after the BB.
Created as high energy gamma radiation after BB
As universe expanded, it stretched into longer and longer wavelengths.
When waves meet a gap in a barrier, they carry on through the gap. However, the waves spread out to some extent into the area beyond the gap. This is diffraction
a gap much larger than the wavelength causes little spreading and a sharp shadow eg light through a doorway
a gap similar to the wavelength causes a lot of spreading with no sharp shadow eg sound through a doorway
The most distant galaxies are about 13 million light years away.
Space, time and matter created by the Big Bang
BIG BANG happened 13,000 million years ago
Light from distant galaxy is red-shifted to longer wavelengths
Edwin Hubble discovered that light from galaxies were red-shifted
Distant galaxies are moving away from us
Speed of distant galaxy is proportional to distance from us
The universe is expanding