Electromagnetic Waves

Electromagnetic Waves

1. Gamma rays and x-rays

   • X-rays pass through soft tissue but are absorbed by bone
     • X-rays produce radiographs
       • Gamma radiation is electromagnetic radiation from radioactive substances
         • Gamma rays can be used to kill harmful bacteria in food, sterilise surgical equipment and to kill cancer cells

2. Visible light and ultraviolet radiation

   • Light from the Sun and light bulbs is called white light, because it has all colours of the visible spectrum on it
     • Ultraviolet (UV) radiation makes some chemicals emit light
       • UV radiation is harmful to the human eye and can cause blindness
         • UV radiation comes from the Sun, and too much of it can cause skin cancer

3. Infra-red waves, microwaves and radio waves

   • All objects emit infra-red radiation
     • The hotter an object is the more radiation it emits
       • Infra-red radiation is absorbed by the skin, which kills skin cells as they heat up
         • Infra-red devices include heaters and remote controls
           • Microwaves are shorter than radio waves in wavelength, even though they come before radio waves in the electromagnetic spectrum. This is why they are called microwaves
             • We use microwaves for communication and heating food in microwave ovens
               • Radio waves are longer in wavelength than microwaves – but appear after microwaves in the electromagnetic spectrum because they have a lower frequency
                 • We use radio waves to carry radio, TV and mobile phone signals
                   • Radio waves are emitted from an aerial
                     • Analogue and digital signals

4. The electromagnetic spectrum

   • The wavelength of a wave is the distance from one wave peak to the next wave peak along the waves
     • The frequency is the number of complete waves passing a point per second
       • We measure frequency in the unit of hertz (Hz) when:
         • - 1 Hz = 1 complete wave per second
           • - 1 Hz = 1 complete wave per second
             • - 1 kilohertz (kHz) = 1000 Hz
               • - 1 megahertz (MHz) = 1,000,000 Hz
     • The speed of a wave is worked out by using: wave speed (m/s) = frequency (Hz) x wavelength (m)
   • Alternatively, the frequency can be worked out by using:
     • frequency = wave speed (in m/s) ________________________________ wavelength (in metres)