Electromagnetic Spectrum Notes

Electromagnetic Radiation Overview

  • Electromagnetic radiation is all around us, essential for modern life.
  • It spans a spectrum from gamma rays to radio waves.
  • Key applications: radio, remote control, text messages, TV, microwaves, X-rays.

Properties of EM Waves

  • EM waves transmit energy and are produced by vibrating charged particles.
  • They travel through the vacuum of space at the speed of light.
  • Key characteristics: wavelength (distance between crests) and frequency (cycles per second, measured in Hertz).
  • Wavelength=speedfrequencyWavelength = \frac{speed}{frequency}

Electromagnetic Spectrum

  • Long waves (radio waves) have low frequency and energy.
  • Short waves (gamma rays) have high frequency and energy.
  • Visible light is a small portion (400-700 nm) that our eyes can detect.
  • Color is determined by reflected wavelengths.
  • Spectral signatures help identify chemical composition and physical properties of objects.

Radio Waves

  • Discovered by Heinrich Hertz; used in radio astronomy.
  • Longest EM waves, vary greatly in length from centimeters to kilometers.
  • Detected by large antennas, including arrays that act as immense collectors.
  • Used to discover pulsars, giant plasma clouds, and quasars.

Microwaves

  • Wavelengths range from 30 cm to 1 mm; used in Doppler radar for weather forecasting.
  • Penetrate clouds and are used for satellite measurements of sea ice and soil moisture.
  • Used in global positioning systems (GPS).
  • Cosmic microwave background radiation supports the Big Bang theory.

Infrared Waves

  • Discovered by William Herschel; wavelengths from 760 nm to 1 mm.
  • Sensed as heat; emitted by objects, including humans.
  • Used to see through gas and dust in space (e.g., Spitzer telescope).
  • Help study Earth's energy budget, including reflected and emitted radiation.

Visible Light

  • Wavelengths range from 380 nm (violet) to 700 nm (red).
  • Composition of stellar objects reveals temperatures.
  • Used to study changes on Earth, assess volcanic damage, and monitor cities and forests (e.g. Landsat).
  • Laser altimeters can map topography.

Ultraviolet (UV) Rays

  • Discovered by Johann Ritter; wavelengths from 400 nm to 10 nm (UVA, UVB, UVC).
  • Most UVB and all UVC rays are absorbed by the atmosphere's ozone layer.
  • Used to study the chemistry of the atmosphere and distant star formations (e.g., NASA's Aura satellite).

X-Rays

  • Discovered by Wilhelm Röntgen; wavelengths between 3 and 0.03 nm.
  • Used in medicine and to determine the composition and structure of substances.
  • Detected from hot, energetic objects like pulsars and black holes (e.g., Chandra X-ray Observatory).

Gamma Rays

  • Most energetic EM waves; absorbed by Earth's atmosphere.
  • Produced by radioactive decay, nuclear explosions, and lightning.
  • Used in medicine to destroy cancer cells.
  • Detected by crystal blocks that sense charged particles created by collisions.
  • Used to determine elements on Mars and to study gamma ray bursts from deep space (e.g., Fermi Gamma-ray Space Telescope).