Physic Topic 2 - The Electromagnetic Spectrum

Physic Topic 2 - The Electromagnetic Spectrum

1. Beyond the Visible

   • Infra-red
     • William Herschel (1738 - 1822) was a British Astronomer.
       • He discovered Infra-red by using a prism to split the sunlight into a spectrum and then put a thermometers either side of the spectrum.
         • As he changed the colour from violet to red, he found that the temperature rose.
           • He wondered what would happen if he measured the temperature just beyond the red end on the spectrum, where there was no visible light.
             • He found this gave him the highest temperature and he named it Infra-red, as it was just after the red end of the spectrum.
   • Ultra-violet
     • Johann Ritter (1776 - 1810)
       • He found out about Herschel's work and in 1801 set about trying to find 'invisible rays' at the other end of the spectrum.
         • He used silver chloride, a chemical that breaks down to give a black colour when exposed to light.
           • It was already known that silver chloride turned black more quickly in violet light that in red light.
             • Ritter showed that silver chloride turned black fastest when exposed to 'invisible rays' just beyond violet.
               • It was called Ultra-violet as it is just beyond violet on the spectrum.

2. The Electromagnetic Spectrum

   • Shortest Wavelenght - Highest Frequency
     • Longest Wavelength - Lowest Frequency
       • Radio waves
     • Gamma rays
   • Gamma rays
     • X-rays
       • Ultra-violet rays
         • Visible Light
           • Infra-red
             • Microwaves
               • Radio waves
   • Good
     • Xylophonest
       • Use
         • Very
           • Interesting
             • Musical
               • Rhythms
   • Electromagnetic waves can travel without any particles to vibrate. This means that they can move easily through a vacuum, such as space.
     • All electromagnetic waves travel at 300,000 kilometres per second in a vacuum.

3. Dangers and Uses

   • Gamma rays are used to kill cancer cells.
   • X-rays are used to take photographs of your body and to scan your luggage at airports.
     • Exc
   • Sunlight contains ultra-violet light.
     • Ultra-violet light can also damage our eyes, which can lead to cataracts.
     • Excessive exposure to Gamma rays, X-rays and Ultra-violet rays may cause mutations, or changes in DNA that may kill cells or cause cancer.
   • Infra-red radiation is used in thermal imaging cameras, this means anything that emits heat can be seen in the dark or fog.
   • Ultra-violet is used in the making of bank notes, under UV light the fluorescent markings become visible to the human eye, proving if it is forged.

4. Ionising Radiation

   • Gamma
     • Electromagnetic waves are emitted from the nucleus.
     • It is a particle.
       • It is high energy.
   • Alpha
     • It is a particle.
       • Helium is emitted from the nucleus.
   • Beta
     • It is a particle.
       • Electrons are emitted from a neutron (changing it to a proton).