Properties of Light
Waves and Particles
- Wave model: light exhibits many wave behaviors such as
interference, reflection, refraction, and diffraction
- Particle model: a particle of light is called a photon. Photons do
not have mass, so they are different from regular matter. Photons
are like little bundles of energy.
Electromagnetic Spectrum
- All electromagnetic waves travel at the same speed
(speed of light = 300,000,000 m/s)
- Nothing travels faster than light
- Radio waves: longest wavelength, lowest frequency, lowest
energy. Radio waves are used in communications and radar.
o TV, AM, FM
o Radar uses reflected radio waves to determine the distance
to, and location of, objects
 Used by air traffic controllers to track airplanes and
highway patrol to measure speed
- Microwaves: shorter wavelength, higher frequency and higher
energy than radio waves. Microwaves are used in communications
and cooking.
o Energy in microwaves is absorbed by water, fat, and sugar.
That electromagnetic energy is transferred into thermal
energy.
- Infrared: shorter wavelength, higher frequency and higher energy
than microwaves. Humans cannot see infrared light, but they can
feel it. Infrared light can be felt as warmth.
o Devices that are sensitive to infrared light can reveal images
of objects that show temperature variations.
- Visible Light: the only part of the EM spectrum we can see. Visible
light is made of red, orange, yellow, green, blue, indigo, and violet
(R O Y G B I V)
- Ultraviolet: shorter wavelength, higher frequency and higher
energy than visible light. Sunlight contains ultraviolet light.
o Since it has more energy, UV light is more damaging than
visible light. Things that block out visible light don’t
necessarily block UV light.
- X-rays: shorter wavelength, higher frequency and higher energy
than UV light. X-rays are used in medicine.
o An X-ray image is made by passing X-rays through the body.
Most pass right through, but some are absorbed by bones
and organs. The rays that pass through produce an image.
- Gamma Rays: shortest wavelength, highest frequency and energy
of electromagnetic waves. Gamma rays are used in medicine.
o Gamma rays (Γ) are dangerous to living cells. Gamma rays
can be used to treat cancer by killing diseased cells.