1. OPTICS
Unit 3

2. What is Light?
Light is electromagnetic radiation - a form of energy that behaves both as a particle and as a wave.
Light

3. What is Light?
Unlike most other forms of energy, light does not require a medium for transmission  it can travel through space
Light travels in a straight line
Light is produced by energizing electrons.

4. What is Light? Speed of light = 300 million m/s (300 thousand km/s)
At that speed it would take 1 second to travel 7.5 times around the earth’s equator

5. What is Light?
A Photon is a “package” of electromagnetic radiation. Photons are like light “bullets” that have a range of power based on their wavelength.

6. The Electromagnetic Spectrum
Classifies electromagnetic waves according to the energy of the waves they produce.
Radio waves (very low energy)
Microwaves
Infrared light
Visible light
UV light
X-Rays
Gamma rays
(very high energy)
Increasing Energy
Increasing Wavelength

7. Uses of Electromagnetic Waves – pg. 466

8. Visible Light Light that the human eye can detect
Includes light with wavelengths of 750 nm to 380 nm
White light is composed of a continuous sequence of colours called the visible spectrum
The Visible Spectrum: “Roy G. Biv”
Red  Orange  Yellow  Green  Blue  Indigo  Violet
Increasing Energy

10. How is Light Produced?
Luminous objects produce their own light (Sun, light bulb, fire, etc.)
Non-Luminous objects do not produce their own light, instead they are visible because they reflect light. Most objects are non-luminous.

11. Sources of Light
Incandescence: Production of light as a result of high temperatures
- Ex: incandescent light bulbs, fire, stove burner

13. Sources of Light
Electric Discharge: Production of light when an electric current passes through a gas.
- The type of gas determines the colour produced
- Ex: “neon” lights, lightning

15. Sources of Light
Phosphorescence: A material absorbs UV light and then slowly releases visible light of lower energy over a limited period of time
- Ex: Glow-in-the-dark paint or ceiling stars, rocks, moss

17. Sources of Light
Fluorescence: Release of visible light by a material when it absorbs UV light
- Ex: Compact Fluorescent Lights used in the home require 1/5th the energy of incandescent bulbs to produce the same amount of light

20. Sources of Light
Chemiluminescence: “Cold light” - production of visible light from a chemical reaction that produces little or no heat
- Ex: Light sticks

22. Sources of Light
Bioluminescence: Production of visible light through chemical reactions that occur within living organisms.
- Ex: Fire fly, Angler Fish
bioluminescence

24. Sources of Light
Triboluminescence: Production of visible light by rubbing, crushing, or scratching certain crystals
- Ex: Biting a Lifesaver Wintergreen candy, crushing sugar

26. Sources of Light
Light Emitting Diode (LED): An energy efficient light-bulb that allows energy to pass through a semi-conductive material that only allows electrons to flow in one direction.
- Ex: LED Christmas lights

27. Homework
Read pages
Complete Questions 2-10 (pg. 476)

29. Lasers
Light from a laser is very different than light from an incandescent light bulb.  
Incandescent bulbs emit electromagnetic waves of many different energy levels. They produce white light that illuminates all objects surrounding them in a complete sphere.

30. Lasers
Laser lights produce electromagnetic waves of exactly the same energy level. The waves travel in unison in exactly the same direction. Therefore, laser light is:
 Pure in colour
 Very intense
 Concentrated in one narrow beam

32. Light Rays and Geometric Optics
 Light Ray – A line on a diagram that represents the direction and straight-line path that light travels. (arrow = direction)
 Geometric Optics – The use of light rays to determine how light behaves when it strikes an object
 Incident Light – Light emitted from a source that strikes an object

33. Getting in Light’s Way
Transparency is a measure of how much light can pass through a material.
 A transparent object allows light to pass through it easily, allowing objects behind it to be clearly seen.
Ex: clear glass

34. Getting in Light’s Way
A translucent object allows some light to pass through it, but does not allow you to clearly see objects behind it.
Ex: frosted glass
An opaque object does not allow any light to pass through it. Instead, all incident light is either absorbed or reflected, meaning objects behind it cannot be seen.
Ex: A brick wall

35. Flat Mirrors
 Mirrors produce images. An image is a reproduction of an original object that is produced using light.
 A mirror is any polished surface that can produce a reflection
 A reflection is The bouncing back of light from a surface.

36. Flat Mirrors
In order to see light, some light rays MUST reflect off of a surface and enter your eyes.
 Most mirrors consist of two parts: the front part is a sheet of protective glass, and the back part is a thin, opaque layer of reflective silver or aluminum.

38. The Terminology of Reflection
 Plane Mirror – A flat mirror
 Incident Ray – The incoming ray that strikes a surface (arrow)
 Reflected Ray – The ray that bounces off of a reflective surface (arrow)
 Normal Line – The line that is perpendicular (90°) to a mirror surface. Drawn at the point where the incident ray strikes the surface of the mirror.

40. The Terminology of Reflection
Angle of Incidence – The angle between the incident ray and the normal
Angle of Reflection – The angle between the reflected ray and the normal

42. Homework Read 11.3 – pg. 477-478, questions 1-6

44. 11.6 – Laws of Reflection
1. The angle of incidence equals the angle of reflection
2. The incident ray, the reflected ray, and the normal all lie in the same plane

45. Reflecting Light off Surfaces
Specular Reflection – the reflection of light off a smooth, shiny surface.

46. Reflecting Light off Surfaces
Diffuse Reflection – the reflection of light off an irregular or dull surface which causes light to scatter.

48. Seeing Images
 We are able to see non-luminous objects because they reflect light.
A light source radiates light rays in all directions.
 The light rays that strike the object and reflect into your eyes are the ones that allow you to see the object.

49. Locating Virtual Images in a Plane Mirror
When you look into a mirror, you see an image of a real object called a virtual image.
Virtual Image – an image seen in a mirror that appears to exist “behind” the mirror, but it is not really there.

50. Characteristics of an Image in a Plane Mirror
Lateral Inversion - The virtual image seen in a plane mirror is always backwards and in reverse order compared to the object.

51. The SALT Acronym
When you describe the properties of an image, you must consider four characteristics  “SALT”
Size – compared to object (same, smaller, larger)
Attitude – upright or inverted
Location
Type – real or virtual

52. “SALT” - Plane Mirror Images
An image in a plane mirror is always:
Size – same size as the object
Attitude – upright but laterally inverted
Location – same distance behind the mirror as the object is in front
Type - virtual