CP PHYSICS
ELECTROMAGNETIC WAVES (LIGHT)
Electromagnetic Waves
 moving charged particles create a magnetic field that expands as the
particles accelerate in one direction
 magnetic field collapses when particle slows down, stops, and changes
direction, causes field to expand again
 expanding and collapsing magnetic field generates an electric field which
expands and collapses to produce another magnetic field and so on
 travels at 3.0 x 108 m/s through empty space (c = speed of light)
 travels more slowly through mediums
 energy depends on frequency
7 Types of Electromagnetic Radiation
1. Radio Waves
 lowest frequency, longest wavelength, least energy
 includes TV waves (higher frequencies)
 VHF = very high frequency, UHF = ultra high frequency
 radio waves carry sound waves, sound waves changed into electrical signals
which change the frequency (FM) or the amplitude (AM) of the radio wave
(change back to sound in your radio receiver)
 each radio station issued wafer shaped quartz crystal that vibrates at a
certain frequency, each station has own frequency
CP PHYSICS, ELECTROMAGNETIC WAVES (LIGHT), page 2
2. Microwaves
 frequencies match natural frequencies of molecules (fats, proteins, etc.)
 causes food molecules to vibrate (resonance) making the food cook itself
 food molecules continue to vibrate even after oven stops generating
microwaves – microwave instructions usually include “stand time”
 icebergs give off microwaves
 microwaves match natural frequencies of some pacemakers
3. Infrared Waves
 heat waves – all animals give off infrared
 uses: heat lamps, night vision, alcohol breath test, remote controls
4. Visible Light
 only makes up 1/1,000,000 of EM spectrum
 different frequencies seen as colors (ROY G BIV)
 red = lowest frequency, longest wavelength, least energy
 violet = highest frequency, shortest wavelength, most energy
 produced when electrons make quantum leaps between energy levels
5. Ultraviolet Light
 causes sunburns, damages tissues, can kill bacteria
 UV-B ray more dangerous than UV-A because they have higher frequency
 produced by e-s making larger quantum leaps
6. X-rays
 produced by high speed electrons slamming into a metal plate
 uses: medical x-rays (bones, teeth), airport security
7. Gamma Rays
 highest frequency, shortest wavelengths, highest energy and penetrating
power
 produced by nuclear particles and occur with every nuclear reaction
 used in radiation therapy (kill healthy cells, but kill cancer cells first)
CP PHYSICS
VISIBLE LIGHT
General Characteristics
 one type of electromagnetic (EM) radiation
 frequencies to which human eye is sensitive
 travels through space in straight line at speed of 3.0 x 108 m/s (c)
 equation: c = λf
 transverse wave, but also behaves like a particle
 interaction with materials:
o transparent – all light is transmitted (ex. clear glass)
o translucent – scatters light transmitted (ex. frosted glass)
o opaque – does not transmit any light (ex. brick)
Wave Behavior
 behaves like wave when travels through medium without interacting with
the medium’s particles
 also behaves as wave when traveling through empty space
 does everything other waves do:
o reflects (stays in old medium when hits boundary to new medium)
o refracts (bends as enters new medium)
o diffracts (occurs when going through very small opening)
o interferes (sent thru 2 slits, constructive interference produces
light bands, destructive interference produces dark bands)
Particle Behavior
 discovered in 1900s, occurs when interacts with matter
 only certain colors (frequencies) of light produce photosynthesis when
light absorbed by green leaves
 when certain colors of light shown on metal plate (ex. solar calculators),
electrons jump out of metal atoms and create electric current, violet light
always works but red light never does
 electrons exist in certain energy levels and make quantum leaps to higher
levels when they absorb energy, fall back down to ground level and give off
certain colors of light
CP PHYSICS, VISIBLE LIGHT, page 2
Quantum Theory
 explains how light interacts with matter
 all energy is absorbed or given off by atoms in tiny little bundles called
quanta
 photon = quantum of light energy
 photon’s energy depends on its frequency
o violet light has higher frequency so has more energy than red light
o red light used in dark rooms to develop film because it does not have
enough energy to produce a chemical reaction in photo film
 cannot explain how light behaves like wave through space but as a particle
when interacting with matter
 result = Dual Theory of Light: Light moves through space as a wave and
interacts with matter as a particle.
Production of Light
 Illuminated objects = reflect light, ex. moon
 Luminous objects = objects which emit light, ex. sun
 produced by exciting electrons which make quantum leaps and then fall
back down to lower energy levels giving off light
 different methods to produce light based on how they excite the
electrons: heating gases, heating metal filaments, electricity, ultraviolet
radiation, chemoluminescence, bioluminescence, phosphorescence
Polarization of Light
 only occurs with transverse waves
 polarized materials have long molecules that only allow EM waves of one
direction = polarizing axis
 blocks waves that are perpendicular to polarizing axis
 can test for polarization with a polarized filter – every time filter turned
90o over material, should see all light blocked then all light pass through
and so on
 polarized sunglasses – reduce glare of light reflecting off variety of
surfaces