Light Notes

Light is electromagnetic energy that travels in waves.

Light sometimes acts like millions of tiny particle, and sometimes it acts like a transverse wave.
Label: wavelength, crest, trough, amplitude, midline
How Light Moves
 Light travels in waves.
 It travels in a straight line.
 Light travels as a transverse wave.
 When it hits an object it can be reflected, absorbed, or transmitted.
 As light moves, the particles transfers energy
 Radiation – the transfer of energy as EM waves
The Speed of light
The speed of light is 300,000 km/s. All electromagnetic waves travel at this speed when in a vacuum.
The Colors of Light
 Different light waves have different wavelengths.
 Our eyes interpret different wavelengths as different colors.
 Shortest wavelength – violet
 Longest wavelength - red
 White light – what is seen when all the wavelengths get mixed in equal proportions
 A prism – a tool used to separate the wavelengths of light
Your Eyes
 Only register 3 colors – red, green, and blue
 They are called the primary colors.
 All other colors we see are just a mixture of these three
The Visible Spectrum
 As wavelength decreases frequency increases.
 Visible light is the part of the electromagnetic spectrum that we can see.
 ROY G. BIV - an acronym to help you remember the colors in the visible spectrum.
 Colors of visible light red, orange, yellow, green, blue, indigo, violet
The Electromagnetic Spectrum - the range of frequencies possessed by electromagnetic waves
Mnemonic to remember the order of the EM spectrum waves: (Pick one from the PowerPoint or
make your own)
Raul’s Mother Is Visiting Uncle Xavier’s Garden
Rabid Monkeys In Velvet nderpants eXcrete Goo
Gate X Usually Lets In Most Radiation - this one is backwards – gamma to radio
Wavelength Comparison
Write in a comparison of sizes in the box below for the wavelengths of the electromagnetic spectrum.
Each wave is larger than or smaller than the object listed below:
Radio waves:
microwaves:
infrared:
visible light:
ultraviolet:
> _________
< _________
< _________
< __________
< _________
soccer field
baseball
cell
bacteria
virus
X-ray:
< __________
waer molecule
gamma ray:
< ________
atom
What are examples of things we use today for each of the wavelengths of the EM spectrum?
Radio: TV, radio, cell phones & cordless phone signals
Microwaves: cook food, Doppler Radar, police radar
Infrared: heat treatment for illness, pictures in the dark of body heat, TV remote control
Visible (light): rainbow colors, laser, LED lights, fiber optics
Ultraviolet: suntan, kill bacteria & viruses, detect forgeries for paintings
X-ray: see broken bones, look for hidden bombs
Gamma ray: kill cancer cells & sterilize
Too Much EM?
 The sun is the primary source of EM radiation
 Our atmosphere acts as a shield to most of the dangerous EM waves
 Remember:
 High frequency = more energy
 More energy = more dangerous
Interactions of light and matter
1. Transmitting light
Transmitting light or allowing light to pass through
 Transparent – objects that can be seen clearly through
Examples: water, glass, air
-
Translucent – transmit some light, but do not allow light to travel straight through; The image appears
foggy or fuzzy
-
Examples: frost, chiseled or frosted glass, tissue paper
2. Absorbing light
Absorption is the transfer of light energy into matter
- Opaque – materials that do not let any light pass through them
- Ex. Bricks, rocks, paper
3. Reflecting light
Happens when light strikes an object and bounces off
 Examples: mirror or other shiny surface
 An object must be opaque in order to reflect light
4. Refraction – bending of waves that occur when light changes its medium
Examples: Observing fish in water, prism, pencil in cup of water
5. Diffraction – bending of waves around a barrier
Examples: Radio waves moving around buildings, fuzzy edges around a shadow.
6. Scattering – occurs when light is sent in many directions as it passes through a medium
Light Interactions:
Draw and label the wave patterns for the following terms: absorbed, reflected, refracted, scattered,
transmitted
transmitted
absorbed
scattered
refracted
reflected
Interference
 When two or more waves combine to make a new wave
Can make the wave stronger (constructive interference) or weaker (destructive interference).
 Examples: interference patterns in space tell scientists about the location of other stars and galaxies.
 Wave pool – in some places the waves come together to make a bigger wave, and some places they
flatten each other out.