Electromagnetic Spectrum

• radiation is energy travelling through space
  • it interacts with matter, how it interacts depends on the type of radiation and the type of matter

Electromagnetic radiation

• electromagnetic (EM) radiation is energy transferred by oscillations in the electromagnetic field
• it has both wave and particle properties

Electromagnetic waves

• the electric field ($\vec{E}$) and magnetic field ($\vec{B}$) are perpendicular to each other
• a changing electric field creates a magnetic field, and a changing magnetic field creates an electric field
• like any way, EM waves have wavelength, frequency, speed

Photons

• a particle of EM radiation is called a photon
• all EM radiation travels at the speed of light $(c)$ in a vacuum: $c=3\times 10^8\mathrm{m}/\mathrm{s}=300,000,000\mathrm{m}/\mathrm{s}$
• EM radiation travels slower through matter, like water or glass

The electromagnetic spectrum

• there is a wide range for wavelength, frequency, and energy of EM radiation
• this range is called the electromagnetic spectrum
• shorter wavelength → higher frequency → higher energy photons

Wavelength

• the distance from one peak of a wave to the next peak
• EM wavelengths range from 10^3# meters to 10^{-12}$ meters

Frequency

• the amount of waves over a period of time
• $1\text{hertz}(\mathrm{Hz})$ = 1 cycle/second
• EM frequencies range from $10^4\mathrm{Hz}$ to $10^{20}\mathrm{Hz}$

Energy

• photon energy increases as frequency increases
• one unit used to measure the energy of an individual photon is the electronvolt $(\mathrm{eV})$

Regions of the EM spectrum

• each region/range of the EM spectrum has a name

Radio waves

• longest wavelength and lowest frequency
• AM and FM radio

Microwaves

• higher frequency than radio waves
• WiFi is also in the microwave range

Infrared

• higher frequency than microwaves
• our bodies, and things at “normal” temperatures that we interact with, emit infrared radiation, so we usually associate infrared radiation with warmth

Visible light

• higher frequency than infrared
• the frequencies of the EM spectrum that human eyes can see
  • red — the longest wavelength and shortest frequency
  • violet — the shortest wavelength and highest frequency
  • other colours of the rainbow (ROYGBIV) are in the frequencies in between
  • some colours like white are a mixture of frequencies perceived at the same time

Ultraviolet (UV)

• higher frequency than visible light
• UV light has enough energy to damage living tissue, causing things like sunburns and eye damage
• the sun emits UV radiation and visible light
• most UV radiation is blocked by the Earth’s ozone, but some still gets through

X-rays

• higher frequency than UV light
• x-ray radiation has enough energy to ionize
  • when an x-ray photon hits an atom, it can lose an electron, causing the atom to become an ion
• too much ionization from x-rays can cause cell damage and mutations
  • normal medical x-rays are safe
    • x-ray photons enter tissue, denser tissue (bones) block enough photons to cause a shadow image in sensors

Gamma rays

• the highest frequency/energy radiation in the EM spectrum
• Gamma $\gamma$ photons have enough energy to ionize atoms
• the most dangerous radiation to living tissue
• produced by high energy interactions in space, and radioactive decay (gamma decay) ¹