OPTICS Unit 3

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

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.

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

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.

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

Uses of Electromagnetic Waves – pg. 466

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

11.2 - 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.

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

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

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

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

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

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

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

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

Homework Read pages 463 - 476 Complete Questions 2-10 (pg. 476)

11.3 - 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.

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

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

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

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

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.

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.

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.  

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

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

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

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

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

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.

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.

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.

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

“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