Electromagnetic Spectrum (Physics Topic 2)

Electromagnetic Spectrum (Physics Topic 2)

1. Contribution to the discovery of waves

   • William Herschel (Discovered Infrared Radiation)
     • He directed sunlight through a prism (dividing individual colour) and measured their temperature
     • The experiment was important as it proved there were colours in the light - invisible to the naked eye
   • Johann Ritter (Discovered Ultra-violet)
     • Found after Herschel's discovery. He directed sunlight through prism & measured the rate of reaction of Silver Chloride. Blue end of the spectrum was most reactive.
     • Silver Chloride = black when exposed to sunlight
     • The experiment proved the idea of types of light beyond both ends of the spectrum

2. Electromagnetic waves

   • Tranverse
     • They have both a magnetic and electric effect
     • They don't need to travel through substances - instead they move through vacuums or infrared radiation e.g the sun
   • Speed
     • They travel at the same speed as a vacuum (300,000,000 m/s) nothing can travel faster

3. Electromagnetic spectrum

   • 1. Radio waves
   • 2. Microwaves
   • 3. Infrared
   • 4.Visible light e.g red, yellow, green, blue
   • 5. Ultra-violet
   • 6. X-rays
   • 7. Gamma rays
   • Increasing frequency, decreasing wavelength, increasing energy

4. Excessive exposure to infrared radiation

   • Microwaves - internal heating of body cells
   • Infrared - skin burns
   • Ultra-violet - damage to surface cells and eyes, leading to skin cancer and damaged eyesight
   • X - rays & gamma rays - mutation or damage to cells in the body

5. Uses of electromagnetic radiation

   • Radio waves: broadcasting, communications, satallite
   • Visible light: photography, vision and illumination
   • Infrared: cooking, optical fibres, thermal, security systems
   • Ultra-violet: cooking, detecting forgery, lamps, disinfecting water

6. Ionising radiation

   • Energised particles use energy to detatch electrons from atoms or molecules
   • Produces free atoms (radicals) containing unpaired electrons - chemically reactive due to their electronic srtucture
   • Radiation from alpha, beta and gamma damage living cells
   • During interaction with an atom - it can remove tightly bound electrons. Ionising can be in the form of a particle

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