P13

• X-rays and gamma rays have similar properties because they both: 

  • are at the short-wavelength end of the electromagnetic spectrum 
  • carry much more energy per second than longer-wavelength electromagnetic waves. 
  • travel straight into substances and can pass through them if the substances are not too dense and not too thick
• Ultraviolet waves lie between visible light and X-rays in the electromagnetic spectrum. They can be used for security marking and in sunbeds. Ultraviolet waves can cause sunburn and skin cancer and may be harmful to human eyes.
• The radio and microwave spectrum is divided into different bands. The different bands are used for different communication purposes. This is because the shorter the wavelength of the waves:

  • the more information they carry
  • the shorter their range 
  • the less they spread out
• • The waves used to carry any type of signal are called carrier waves. 
  • Carrier waves are waves that are used to carry information. They do this by varying their amplitude.
• All electromagnetic waves travel through space at a wave speed of 300 million m/s
• • Different parts of the electromagnetic spectrum are hazardous in different ways. Microwave radiation and radio waves penetrate your skin and are absorbed by body tissue, causing internal heating that may cause damage. Infrared radiation is absorbed by skin, and too much will cause you to get burnt.
• •  Microwave transmitters produce wavelengths that are able to pass through the atmosphere. They are used to send signals to and from satellites for TV programmes. Microwaves are also used in microwave ovens for heating food.
• • Radio waves are used to transmit radio and TV programmes.
• • Remote controls for devices like TVs and DVD players use IR. IR can also be transmitted along optical fibres and is used in special cameras that allow people to see in the dark.
• • Mobile phones use microwave radiation and radio waves at near-microwave frequencies. 
• ORDER OF WAVES IN EM SPECTRUM: radio waves, microwaves, infrared, visible light, ultraviolet, x-rays, gamma rays
• electromagnetic waves are electric and magnetic disturbances. they travel as waves and transfer energy from a source to an absorber
• the higher the frequency of an electromagnetic wave, the more energy it transfers
• in EM waves, the shorter the wavelength, the higher the frequency. energy of waves increase as frequency increases
• Infrared radiation is emitted by all objects. the hotter the object, the more IR it emits
• microwaves are used for satellite phone and TV signals because they travel between satellites in space and earth
• optical fibres are thin, transparent fibres that are used to transmit communication signals by light and IR.
• optical fibres carry more info than radio and microwaves and are more secure because waves stay in fibre
• x-rays are produced when electrons or other particles moving thru at high speeds are stopped
• x-ray tubes are used to produce x-rays
• x-rays are used to make images of bone to check for fractures and detect cracks in metal objects
• gamma rays are produced by radioactive substances when unstable nuclei release energy
• gamma rays have shorter wavelengths than X-rays
• gamma rays are used to kill harmful bacteria in food which prevents food poisoning and to sterilise surgical instruments and can kill cancer cells
• when gamma ray and x-rays pass thru substances they ionise them
• lead absorbs x-rays and gamma rays so lead screens are often used to shield people who work with these
• people who work with ionising radiation wear a film badge. the radiation exposes the film in the badge so the worker's exposure can be monitor
• x-rays pass thru soft tissue but are absorbed by bones, teeth and metal objects that aren't thin so are used to check fractures as they are reflected at these points