1. Unit 3 Light and Optical Systems

2. Topic 1 : What is Light? Light The form of energy we can see BBC video
What are some natural light sources?
Natural light sources
Sun
Fire
Stars
Glow-worms
Lightning
Magma
What are some artificial light sources?
Artificial light sources
Light bulb
Cameras
Stoves
Televisions

3. First Basic Principle of Light
Light is a form of energy and when it reaches a surface it can be absorbed and transformed into other forms of energy
Solar cells change light into electricity
Trees change sunlight into chemical energy
Sources of Light
1. Incandescent Sources
An object heated to such a high temperature that it emits visible light
Light bulbs
Candle flames
2. Fluorescent Sources
When invisible ultraviolet light is absorbed by the particles of an object. The object then emits some of the energy as visible light.
Fluorescent light bulbs

4. 3. Phosphorescent Sources
The emission of light following exposure to and removal of a source of radiation.
Inner surface of televisions and computer screens
Main difference between phosphorescent and fluorescent is – particles in a fluorescent source release their light immediately
4. Chemiluminescent Sources
The emission of light resulting from chemical action and not involving heat
Glow sticks
5. Bioluminescent Sources
An organism that relies on chemical reactions inside its body to produce light
Jelly fish
Squid surf

5. Take a break

6. The Ray Model of Light
The ray model of light helps you to predict where shadows will form and how large they will be
Light travels in straight lines
Objects farther away from the light source cast a smaller shadow and objects closer to the light cast a larger shadow
The ray model also helps you understand what happens when light reaches different materials
Light continues in a straight line through transparent materials
Light travels through translucent materials but the light is scattered and images aren’t seen well
Light does not travel through opaque materials and they cast shadows

7. Topic 2 : Reflection Reflection
Process when light hits a surface and bounces back off that surface
Analyzing Reflection
Draw the picture in figure 3.15 on page 189
The ray that comes from the light source and hits the surface is called the incident ray
The ray that bounces off the surface is called the reflected ray
The line that is at a 90 degree angle to the reflecting surface is called the normal line
The angle between the normal line and the reflected ray is the angle of reflection
The angle between the normal line and the incident ray is the angle of incidence

8. The Law of Reflection
The angle of reflection equals the angle of incidence
Ex. If the angle of incidence is 60˚ then the angle of reflection is 60˚

9. Forming an image
Two important facts about how images form are:
Light reflects off all parts of an object in all directions. All the rays from the object reflect off the mirror according to the law of reflection. The rays that reach your eye appear to be coming from behind the mirror because your mind knows that light travels in a straight line.
Images in a mirror appear to be the same size as the reflected object and come from an equal distance from behind the mirror.
To summarize – Objects appear to be behind the mirror and the objects appear to be equal size and from an equal distance behind the mirror.

10. Take a break

11. Curved Mirrors
Convex Mirrors
Convex mirrors bulge out
Images in a convex mirror appear smaller and farther away
Convex lenses are used :
- in stores for security
- side mirrors in cars
Concave Mirrors
Concave mirrors bulge in
Images in concave mirrors appear to be closer than they actually are
Concave mirrors are used on side mirrors in cars, these are often labelled – Objects appear closer than they actually are and concave mirrors are also used in shaving / make up mirrors.

12. Rough Surfaces
Light reflects off rough surfaces in many different directions
When reading something on paper, the white paper reflects light off in all directions...however, the black absorbs the light and doesn’t reflect so therefore you pick up the image of the letters in between the reflected light. This creates letters and images on paper.
Using the Reflections
Reflections are used in everyday life in the following ways:
Reflectors on bikes so people can see you in the dark
Reflectors on clothes so you can be seen in the dark
Lining up a shot while playing pool
Traffic signs so we can see them at night
Mirrors

13. Review assignment for marks:
Topic 1 Review on page 187
Questions 1 , 3, 4, 6 and the answer the following:
What are the 5 sources of light and give one example of each?
Topic 2 Review on page 199
Questions 1, 2, 3 and 4 (only drawings 1 and 2 – need protractor for this)

14. Take a break

15. Topic 6 : The Source of Colors
The Spectrum
The spectrum is the colors that appear when white light is refracted.
The seven colors are red, orange, yellow, green, blue, indigo and violet. The memory aid to remember is ROY G BIV
Seeing Red
An object is the color of the light that it reflects.
Example:
A tomato appears red because it reflects red light and absorbs the other colors.
White paper reflects all light so it appears white. All the colors combined create white light.
Black absorbs all light so it appears black.

16. How we see color
Rods are structures that help detect light and cones are structures that help detect colors.
Hint...cones start with C and so do colors.
Rods and cones are located in the retina.

17. Topic 7 : The Wave Model of Light
Looking at Wavelength
Definitions of:
Crest – The high parts of a wave
Trough – The low parts of a wave
Wavelength – The distance from crest to crest
Amplitude – The height or depth of a wave from rest position
Frequency is the rate at which a wave moves up and down. Frequency is measured in hertz or cycles (cycles are the movement of a wave from one crest to the next crest or one trough to the next trough) per second.
A buzzer at 900 times/second = 900 hertz
A guitar string at 880 times/2 seconds = 440 hertz
A ball that bounces 10 times/50 seconds = 0.2 hertz

19. Wave Model of Light
The wave model of light says that light travels in waves.
How far light spreads out depends on how long the wavelengths are. Waves with longer wavelengths spread out more.

20. Take a break

21. Light Waves in Action
Shorter wavelength colors such as blue and violet hit particles in the sky and reflect back into space.
Longer wavelength colors such as red and orange miss more of these particles and therefore are seen by the eye.
Laser Light
Laser light emits light of only one wavelength.
Other light sources emit light of different wavelengths.
Light of one wavelength is called coherent.
Lasers can be used for:
Scanners in stores
To use as a surgical tool
Measure the speed of cars

22. Topic 8 : Beyond Light
The Electromagnetic Spectrum Arrangement of visible light and invisible forms of radiant energy according to wavelength. Decreasing Wavelength Increasing Frequency Visible Light
Radio Waves
Infrared
Ultra Violet
X Rays
Gamma Rays

23. 1. Infrared Radiation
Heat Radiation
Uses of Infrared Radiation
Motion detectors
Burglar alarms
Heat lamps
Thermographs
2. Radio Waves
A wave useful for carrying sounds or pictures through the air
Uses of Radio Waves
Broadcasting radio and T.V programs
Radar
Microwave ovens for cooking (microwaves are shortest wavelength and highest frequency of radio waves)

24. Take a break

25. 3. Ultraviolet Radiation
Energetic form of radiation that causes tanning
Depletion of the Ozone layer
Ozone in the atmosphere protects us from Ultraviolet radiation
UV radiation causes tanning
Too much UV radiation can cause cancer
4. X Rays
Radiation that can penetrate skin and muscle
Uses of X Rays
Used in hospitals and dentist offices

26. 5. Gamma Rays
Gamma rays result from nuclear reactions and can kill cells
Use of Gamma Rays
Used to treat cancer cells with radiation therapy

27. YOU ARE NOW GOING TO DO: TOPIC 3,4,6,7,8 REVIEW YOU CAN DO THIS WITH A PARTNER!!