EMR notes

• radios detect radio waves
• cellphones use what used to be television signals
• cordless home phones use low energy microwaves
• in the electromagnetic spectrum, as you move from one end to the other, you'll notice the frequency increase while the wavelenght decreases
• wavelenght and frequency are inversely proportional
• energy and frequency are directly proportional
• radio waves

  • frequency range - 60HZ - 1THz
  • wavelenght range - 1,000,000 m - 0.0001 m
  • source - low frequency vibrations of e¬ in electrical circuits
• since radio waves cannot penetrate metal, we need external antennae to detect them
• radio waves CAN penetrate human flesh, but does not affect it
• MRI machines use radio waves with ^ = 4m (^ = wavelenght)
• microwaves

  • frequency range - 1GHz - 1THz
  • wavelenght range - 1m - 0.01m
  • source - high frequency vibrations of electrons in specialized electrical circuits
  • effect on living tissue - can be dangerous
• At around 2500MHz, a microwave will make a water molecule spin

  • this is how the microwave oven works - it speeds up the water molecules
  • faster moving particles = higher temperature
  • these specific microwaves are dangerous to living tissues that contain water
• microwaves outside of that frequency don't have any effect on water, but can penetrate rain, mist, fog

  • due to their higher energy and greater penetrability, microwaves are used for communication
• infrared radiation

  • frequency range - 1 THz - 1 PHz
  • wavelenght range 0.0001 m - 0.000001 m
  • source - vibrations of particles in warm objects
  • effect on living tissue - can be dangerous to over-exposure
• as (IR) gets warmer (more energy), its frequency increases, and eventually can see it as the color red
• visible light

  • frequency range - 1 PHz
  • wavelenght range - 700 nm - 400 nm
  • source - hot objects (filaments, candles, stars)
  • effects on living tissue - can excite electrons into higher energy levels
• visible light is not strong enough to remove electrons from atoms a.k.a (ionize)
• visible light can move electrons into higher energy levels. when those electrons relax back to their ground state, they release that energy
• unless you are looking directly at a light source, you are actually only seeing the light that is reflected off the surface of an object
• a photon is a massless particle of light
• below visible light, EMR acts mostly like a wave. Above, it is more of a particle
• visible light behaves like a mixture of waves and particles
• ultraviolet rays (UV)

  • frequency range - 10(15) to 10 (18) Hz
  • wavelenght range - 10 (-6) to 10 (-9) m
  • source - very hot objects (stars, welding arcs)
  • effect on living tissue - can damage DNA and cause cancer
• ultraviolet means above violet. Therefore these are photons of light with slightly more energy than violet light
• UV light spans a broad range of energies and can be further divided into sub-ranges

  • UVA photons have the lowest amount of energy
  • UVB and UVC can cause cancer
• UVC is absorbed by the ozone layer
• UVA and UVB are absorbed by plants to drive photosynthesis as plant tissue cant be harmed by these rays only human skin cells can
• UVC photons have a lot of energy that they can ionize molecules

  • that means they can remove electrons to create ions. This usually leads to unwanted chemical reactions which create unwanted tissues aka cancer
• not all radiation penetrates the Earth's atmosphere

  • Mostly just visible light, radio waves and some UV that make it to earths surface
• x-rays

  • frequency range - 10 (18) to 10 (20) Hz
  • wavelength range - 10 (-9) to 10 (-11)
  • source - high energy e- striking a metal object
  • effect on living tissue - ionizing radiation; damages tissues
• x-rays can be used in radiation therapy; targeted x-rays can kill cancer cells.
• x-rays can't penetrate lead and other heavy metals
• we allow exposure to x-rays because:

  • medical imaging has many benefits (broken bones, cavities, tumors)
  • the negative effects of x-rays take decades of accumulation to show any effects
  • the benefits outweigh the risks for most people, but limited exposure is preferred
• Gamma Rays

  • frequency range - 10 (19) to 10 (23) Hz
  • wavelength range - 10 (-10) to 10 (-14) m
  • source - radioactive nuclei
  • effect on living tissue - ionizing radiation;damages tissues (can cause cataracts)
• y-rays (gamma rays) have 1000 times more energy than x-rays
• y-rays don't reach the Earth's surface as they're absorbed by the atmosphere
• targeted y-rays are an effective way to kill cancer cells
• cobalt - 60 is a radioactive isotope that emits y-rays
• frequency is inversely proportional to wavelength

  
• ^ = wavelength (m)

  f = frequency (Hz)

  v = speed (c = the speed of light) {m/s}