1. LIGHT
Chapter 14

2. What is Light?
1. Is both a wave and a particle
 Acts like a wave:
 Carries energy (heat)
 Has color
 Different l and f
 Can be reflected and refracted
 Shows interference (destructive & constructive)
 Acts like a particle:
 Travels without a medium (space)
2. Considered a photon (a packet or unit of light)

3. 3.Transverse wave on 2 planes of motion
 electric field (on vertical plane)
 magnetic field (on horizontal plane)

4. How is light made?
 Atoms
 Electrons orbiting around nucleus
 Farther e- are from the nucleus, the more energy they
have
 Move towards nucleus, they lose/give off energy

5. Light Examples
 Light bulbs
1. Incandescence - makes light with heat
 Filament inside is heated
 e- in filament gain and lose energy, which gives
off light
 Give off A LOT of heat, wastes energy
2. Fluorescent - add energy to e- inside a gas
 Little heat created, so little is lost
3. LED – e- constantly moving in semiconductor
 ‘Light emitting diode’

6. Light Examples
4. Photoluminescence – process of creating light
 Objects contain Phosphorus
 Glow in the dark objects
 Exposed to any light, e- gain energy
 Lose energy very slowly
 Once energy is gone, it can be “recharged” by
putting it back in the light

8. The Speed of Light (“c”)
 The “universal speed limit” – nothing in universe
can go faster than light
 Unaffected by any medium
 Is 3 x 108 m/s (300,000,000 m/s)
 Can circle the Earth 7.5 times in 1 sec
 Light from the sun is 8 minutes old
 We use light to determine distance in space:
 1 light year = the distance light travels in one year

9. What can we see?
 We see white light
 Separate white light with a prism through refraction
 Get different colors (ROY G BIV)
 Also called visible light

10.  Colors have different energies (f & l)
 Think about fire –
 red flames are coolest (outside of flame)
 blue are hottest (middle of fire)
 As you move from red to blue:
 light GAINS energy, so shorter l
 White light is hottest since made up of all colors
 Color can also tell us other things:
 We can determine their chemical make-up based on
the colors we see (i.e. stars)

11. Visible and Invisible Light
 The amount of energy given off by e- varies
greatly
 Leads to different l
 Small l are measured in nanometers (nm)
 1 nm = 1 x 10-9 m (0.0000000001 m)
 Whole range of energy is known as the
Electromagnetic radiation (EMR)
 All light in this spectrum travels at (c)

12.  EMR
 Organized longest l to shortest l
 Longer l = low energy, low frequency
 Shorter l = high energy, high frequency
 DANGEROUS STUFF!

13. 1. Radio waves: very high l, low energy waves
 Used to transmit radio andTV signals
 Radio towers are so tall – to make long radio waves
2. Microwaves:
 Used to cook food (by vibrating water molecules)
 Cell phones transmissions

14. 3. Infrared:
 Shows heat signatures of objects
4.Visible Light:
 What we see – colors

15. 5. Ultraviolet Light (UV):
 Causes sunburns and skin cancer
 Much of this is absorbed by the ozone layer
6. X-Rays:
 Small enough l to penetrate materials and tissues
 Medical use: see bones or teeth

16. 7. Gamma Rays:
 most powerful & most dangerous
 Lowest l & highest energy
 Emitted from nuclear reactions
 Can break cellular bonds and cause mutations (cancer)
 Medical use: used to help treat cancer