1. The Wave Model of Light
Topic #7

2. Looking at Wavelength
Light does not appear to travel in straight lines
When light passes through a small opening, it spreads out around each side of the opening
Light does not travel as a straight stream of particles, but as a WAVE

3. Features of a Wave The high parts of a wave are called crests
The low parts in between crests are called troughs
A stationary object will simply rise and fall with the wave and not move horizontally (see next slide)

4. Features of a Wave
The same thing would happen to you if you were floating or in a kayak!

5. So in this picture, the duck simply moves up and down as the wave passes
The distance from crest to crest or from trough to trough, is called the wavelength.

6. If the wind starts blowing, the water will become rougher
Higher crests and deeper troughs will soon form
The height of the crest or depth of the trough from the rest position is called the amplitude

7. The rate at which the duck moves up and down is called the frequency (f)
Frequency is the number of cycles completed by a vibrating object in a unit of time
Frequency is normally measured in hertz (cycles per second)
- if something vibrates 20 times in a second, its frequency is said to be 20 hertz (20 Hz)

8. The Wave Model of Light
As this title says, this model of how light behaves is just that, a model.
This model explains a great deal about how light behaves, but not everything about light!!!
When light passes through a small opening, the waves spread out
How far the waves spread out depends on the wavelength of the wave

9. Wave Model of Light (cont.)
Waves with short wavelengths spread out very little.
Waves with long wavelengths spread out more
Different colours in the spectrum have different wavelengths and therefore, behave differently

10. Laser Light Laser light was first used in 1966
Laser stands for “light amplification by the stimulated emission of radiation
Incandescent bulbs give off many different colours
This means that all sorts of different wavelengths and frequencies are emitted

11. The waves are therefore, all jumbled and the crests from one might overlap the trough of another
These kinds of lights produce waves that actually work against each other
They are said to be incoherent

12. Laser light emits waves with only one frequency or wavelength
All the waves line up to work together
Therefore, this light is said to be coherent

13. Uses for Lasers Lasers are used for many purposes
How many can you come up with?

14. Uses for Lasers Lasers are used for many purposes
How many can you come up with?
- supermarket scanners
- CD’s
- police speed detectors
- scalpels in modern surgery
- cutting metal
- and also………..

15. And…..

16. And…