Light can act as both a wave and particle. It is made up of photons that travel in transverse waves. Light is produced when electrons in atoms gain and lose energy by moving closer to or farther from the nucleus. Different light sources like incandescent bulbs, fluorescent bulbs, and LEDs produce light through various electron energy transfer processes. Light travels at the universal speed limit of about 300 million meters per second. Only a small portion of the electromagnetic spectrum, called visible light, is visible to the human eye.

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