Chapter 8: Electromagnetic Waves

Chapter 8: Electromagnetic Waves

1. Electromagnetic Spectrum

   • RMIVUXG

2. Light and Colour (Visible)

   • Light from ordinary lamps and from the sun is called white light, this is because it has all the colours of the visible spectrum in it. The wavelength increases across the spectrum as you go from violet to red.

3. Infrared Radiation

   • All objects emit infared radiation, the hotter an object is, the more infared radiation it emits. Infared radiation is absorbed by the skin. It can damage or kill skin cells because it heats up the cells
   • Infrared devices
     • Remote control handsets for tv and video equipment transmit signals carried by infrared radiation. When you press a button on the handset, it sends out a sequence of infrared pulses.
     • Infrared scanners are used in medicine to detect 'hot spots' on the body surface. These hot areas can mean the underlying tissue is unhealthy.
     • Infrared cameras to see people and animals in the dark

4. Microwaves

   • You can use microwaves for communications, e.g. Satellite tv, because they can pass through the atmosphere and reach satellites above the earth, because they don't spread out as much as radio waves they are used to beam out signals

5. Radiowaves

   • Radio wave frequencies range from 300 000 Hz to 3000 milllion Hz They are longer in wavelength and lower in frquency than microwaves.
   • You can use radio waves instead instead of cables to connect a computer to other devices like a printer.
   • Microwaves and radio waves can be hazardous because they penetrate our bodies and heat the internal parts of our bodies

6. All electromagnetic waves travel at a speed of 300 million m/s through space or in a vaccum

   • wave speed = frequency x wavelength

7. Ultraviolet

   • UV wavelengths are smaller than visible light wavelengths are smaller than visible light wavelengths, UV carries more energy than light rays
     • Too much UV radiation causes sunburn and can cause skin cancer.
     • If you stay outdoors in summer, use skin creams to block UV radiation and prevent it reaching your skin. If you use a sun bed to get a suntan, don't exceed the recommended time, you should also wear special goggles to protect your eyes

8. X-rays and Gamma Rays

   • Killing harmful bacteria in food, exposing food to gamma radiaton kills 99% of disease carrying organisms
     • Sterilising surgical instruments, this helps to stop infection spreading in hospitals.
       • Killing cancer cells, a narrow beam of gamma is directed straight at the tumour, the beam is aimed at it from different directions so as to kill the tumour but not the surrounding tissue.
   • They both are at the short-wavelength end of electromagnetic spectrum, and carry much more energy per second than longer-wavelength electromagnetic waves.
     • X rays are produced when electrons or other particles moving at high speeds are stopped
       • Gamma rays are produced by radioactive substance when unstable nuclei release energy
   • safety
     • X-rays and gamma rays passing through substances can knock electrons out of atoms in the substance. The atoms become charged because they lose electrons
       • If ionisation happens to a living cell, it can damage or kill the cell, and for this reason exposure to too much radiation is dangerous and can cause cancer. High doses kill living cells and low doses cause cell mutation and cancerous growth.

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