Electromagnetic waves

• electromagnetic waves

  • transverse waves
  • transfer energy from source to absorber
  • eg microwave - transfer energy from source (microwave) to the absorber (food)
  • eg solar panels - light waves transfer energy from source (sun) to the absorber (solar panels)
• Each colour of light when split has a different wavelength and frequency

  
• Frequency/wavelength of colour of light

  1. red | lower frequency
  2. orange | longerwavelength
  3. yellow |
  4. green |
  5. blue |
  6. indigo | higher frequency
  7. violet | shorterwavelength
• Electromagnetic spectrum

  
• Electromagnetic spectrum

  1. Radio Raw
  2. microwaves Meat
  3. infrared Is
  4. visible light Very
  5. ultraviolet unsanitary
  6. x-rays eXcept
  7. gamma rays Giraffe
• Frequency increases from radio waves to gamma rays
• Electromagnetic waves do not need a medium to travel in so they can travel in a vacuum (eg space) but all waves at a the same speed
• Radio waves:

  • Used to transmit radio and TV signals
  • Can travel long distances before being absorbed
  • Can spread out between hills
• Microwaves:

  • Heat food because water molecules in food absorb energy of waves, causing an increase in heat
  • Used for satellites in space
  • Microwaves pass through Earth's atmosphere
• Infrared:

  • Used in electrical heaters and ovens to cook food
  • Energy from infrared is easily absorbed
• Visible light:

  • Used for communication using fiber optics
  • Optical fibers are very thin strands of glass
  • Can transmit light down the fibers to carry information for telephone and cable TV signals
  • Short wavelength allows it to carry lots of information
• Ultraviolet:

  • Used in energy-efficient lightbulbs
  • Ultraviolet light is created inside the bulb
  • Short wavelength carries more energy than visible light
  • Energy is converted into visible light, requiring less energy than a normal light bulb
• 1. rays / Gamma rays:

  • Used in medical imaging
  • X-rays for broken bones, gamma rays to detect and treat cancers
  • Very penetrating
• When EM waves are generated or absorbed, changes take place in atoms or in the nuclei of atoms
• Generation EM waves - atom change

  • when we heat atoms we cause electrons to move from one energy to a higher one
  • when the electron returns to original energy level it generates an EM wave
  • so a change to the atom generates an EM wave
• Generation of EM waves - changes in nuclei in atom

  • gamma rays can be emitted from the nucleus of radioactive atoms
• Absorption in EM waves

  • this energy caused when energy is absorbed from the WM wave it causes change to atom
  • eg - electrons can change energy levels
• Hazards of EM radiation waves

  • ultraviolet increase risk of skin cancer - cause skin to age prematurely
  • x - rays and gamma rays - ionising radiation (they knock electrons off atoms) this can cause mutation of genes and increase risk of cancer
• EM radiation waves

  • needs dosage so its not harmful
  • dose of radiation - sieverts (Sv) or millisieverts (mSv)
• Production of radio waves -

  • when electrons oscillate (move forward and backwards) in electrical circuits
  • when the radiowaves are absorbed (eg by electric circuit in an aerial ) they cause electrons in the aerial electric circuit to oscillate
  • = an alternating current with the same frequency as the radiowaves

  
• Emission and absorption of infrared

  • all bodies (objects) emit and absorb infrared radiation
  • the hotter the body = the more radiation it radiates
  • a good absorber is also a good emitter of radiation