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)

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