Unit 8 How we use light to see To the physicist the colors of things are not in the substances of the things themselves Color is in the eye of the beholder and is provoked by the frequencies of light emitted or reflected by things ID: 384165
Download Presentation The PPT/PDF document "Reflection and Refraction" is the property of its rightful owner. Permission is granted to download and print the materials on this web site for personal, non-commercial use only, and to display it on your personal computer provided you do not modify the materials and that you retain all copyright notices contained in the materials. By downloading content from our website, you accept the terms of this agreement.
Slide1
Reflection and Refraction
Unit 8Slide2
How we use light to see.
To the physicist, the colors of things are not in the substances of the things themselves.
Color is in the eye of the beholder and is provoked by the frequencies of light emitted or reflected by things.
White light – all frequencies combined.
Black – absence
of light.Slide3
Wave characteristics of Light
Light can:
Refract – Bend when hitting a new medium at an angle.
Examples: pencil in glass of water (air to water)
Reflect – bounce back after hitting a new medium.
Examples: mirror (air to metallic painted glass)
air to water or any reflective surfaceSlide4
Reflection
Reflection-
The bouncing back of a particle or wave that strikes the boundary between two media.
- In terms of light it is the photons that strike the
boundary between two media.
media such as:
metals, water, glass
any reflective surfaceSlide5
Reflection
Media between
air and waterSlide6
The frequencies of Light
R
O
Y
G
B
I
VSlide7
Reflecting and Absorbing
Black materials
absorb light
Black materials
hold energy
White materials
reflect lightSlide8
Reflection
Most materials absorb light of some frequency and reflect light of the rest.
The color of the object is determined by the reflected frequency.
Example: If an object has red frequencies and all other frequencies are absorbed, then the object will appear red.Slide9
The Law of Reflection
The Law of Reflection
The angle of incidence for a wave that strikes a surface is equal to the angle of reflection.Slide10
Reflection
Ray
A thin beam of light, represented as a vector arrow on light ray diagrams.
Normal
A line perpendicular to a surface.
Angle of incidence
Angle between an incident ray and the normal to a surface.
Angle of reflection
Angle between a reflected ray and the normal to a surface.Slide11
Refraction
Refraction
The change in direction of a wave as it crosses the boundary between two media in which the wave travels at different speeds.
As light passes through varying mediums, temperatures and densities of the same medium it will change direction.
When the wave slows down – it bends toward the normal
When the wave speeds up – it bends away from the normal.Slide12
RefractionSlide13
RefractionSlide14
Total Internal Reflection
At the boundary between water and air or glass and air light will refract.
As the angle in which the light enters these mediums is changed, the angle at which is bent changes also.
If the angle of the incident ray is increased from the normal the reflected ray no longer exists the medium, but will reflect back.Slide15
Total Internal Reflection
This is called total internal reflection.
This occurs when the light rays are at the critical angle. (around 42
o
between water and air or glass and air).Slide16
Reflection, Refraction & Total Internal Reflection
https://youtu.be/gDA_nDXM-ck
https://youtu.be/2kBOqfS0nmE?list=RDgDA_nDXM-ck