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Unit 3: OpticsChapter 4
History of Light
https://www.youtube.com/watch?v=J1yIApZtLos
History of Light
• Early philosophers (Pythagoras) believed light was made up of tiny
particles
• Later scientist found evidence that light also behaved like a wave.
• We now understand that light can act both as a particle and a wave.
History of Light
• Light: A form of energy that can be described as both a wave and a particle.
Visible light is a type of light that can be detected by the human eye.
History of Light
Galileo was the first person to try to measure the speed of light
• 2 people stood on opposite hilltops with lanterns
• uncovered the lanterns, timed how long it took for the light to reach the other person
• used the distance between hilltops and the time to calculate the speed
• This experiment did not work
Why?
History of Light
Albert Michelson was the first person to successfully measure the
speed of light
Speed of light : 1 000 000 000 km/ hr Speed of sound 1 200 km/hr
History of Light
In a storm, which do you experience first; the sight of the lightning or the sound of thunder? why?
Wave Model
• Wave model of light
Wave Model
Terms:
Crest: The highest point in a wave (the peak)
Wave Model
Terms:
Crest: The highest point in a wave (the peak)
Trough: The lowest point in a wave
Wave Model
Terms:
Crest: The highest point in a wave (the peak)
Trough: The lowest point in a wave
Amplitude: The height of a wave. Measured form the rest position to the crest.
• measures the energy of the wave (higher amplitude= more energy)
Wave Model
Terms:
Wavelength: The length of one full wave.(from crest to crest or trough to trough)
Usually measured in metres
Wave Model
Terms:
Wavelength: The length of one full wave.(from crest to crest or trough to trough)
Usually measured in metres
Frequency: The number of wavelengths that pass a point in 1 second
Measured in Hertz (Hz)
• High frequency waves have shorter wavelengths
• Low frequency waves have longer wavelengths
Wave Model
Label the waves on your worksheet and complete the measurements
Light
Electromagnetic Spectrum: All of the different wavelengths of electromagnetic radiation (a type of energy) arranged from longest to shortest wavelength
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Light
Visible Light
•In the middle of the electromagnetic spectrum
•The only wavelengths we can see with the human eye
Visible Spectrum: ROY G BIV (Red, Orange, Yellow, Green, Blue, Indigo, Violet)
Properties of Light
In the previous class we experimented with light and saw how it interacted with different materials
What observations did we make?
How did light interact with each of the following?
•Mirrors•Prisms• Fabric•Paper
• Solid objects•Glass•Water• Spoon
Properties of Light
Reflection- Light bounces off some surfaces (ex. Mirrors)
Properties of Light
Reflection- Light bounces off some surfaces (ex. Mirrors)
Refraction- Light bends as it moves form one material to another
(ex light moving from air to water)
Properties of Light
Reflection- Light bounces off some surfaces (ex. Mirrors)
Refraction- Light bends as it moves form one material to another
(ex light moving from air to water)
Dispersion- Light can be separated into its different wavelengths or colours (ex. Rainbows)
Properties of Light
Travels through a vacuum- Light can travel through empty space
• unlike sound which needs a medium (air or water) to travel through
Properties of Light
Travels through a vacuum- Light can travel through empty space
• unlike sound which needs a medium (air or water) to travel through
Rectilinear Propagation- Light travels in a straight line
• This created shadows
Properties of Light
Absorption- Different materials absorb light by different amounts
Unit 3: OpticsChapter 5
Modeling Light
• Particle model- early scientist not wrong, explains some properties that a waves cannot
Modeling Light
• Particle model- early scientist not wrong, explains some properties that a waves cannot
• Wave model- accounts for different frequencies, wavelengths and therefore colour
Light behaves like both a particle and a wave
Modeling Light
Light behaves like both a particle and a wave- To simplify and help us understand how light behaves we use
the Ray Model
Ray model :represents light as a straight line or ray showing the direction of travel
Modeling Light
We can use the ray model to show the different properties of light
Rectilinear Propagation
Modeling Light
Light travels through objects to different degrees
Images are distorted
Modeling Light
Transparent
Clear windows Water
Translucent
Stained glass Frosted glass Wax paper
Opaque
Cardboard Wood
Modeling Light
Reflection- light bounces off of a surface
mirror
Modeling Light
Refraction- light is bent as it passes through different mediums
Air
Water
Modeling Light
Parts of a reflection diagram:
Incident Ray: Incoming ray from the object into the mirror
Reflected Ray: Outgoing ray being reflected from the mirror
Normal
Modeling Light
Parts of a reflection diagram:
Normal
Normal: Line drawn at right angle to the
mirror
Angle of incidents: Angle between incident
ray and normal
Angle of reflection: Angle between reflected
ray and normal
Law of reflection
Law of reflection: when a ray is reflected from a smooth surface the angle of reflection is equal to the angle of incidence
Normal
Law of reflection
Law of reflection: when a ray is reflected from a smooth surface the angle of reflection is equal to the angle of incidence
400
400
Normal
Reflection
The two types of reflection;
Specular smooth surfacerays remain together
• Calm water• Plane mirrors• Glossy
photographs
Diffuse rough surfacerays are diffused in different directions
• Textured countertop
• Matte photographs
Types of Mirrors
Plane Concave Convex◦ Flat Surface ◦ curved inward ◦curved outward
Types of Mirrors
Plane Concave Convex◦ Flat Surface ◦ curved inward ◦curved outward
Examples:Bathroom mirror flashlight, projector bus mirrors
security mirrors
Types of Mirrors
We draw ray diagrams of mirrors to see where and how an image will be reflected
Types of Mirrors
We draw ray diagrams of mirrors to see where and how an image will be reflected
Remember:
Normal
Drawing a ray diagram for a plane mirror
Rule: Angle of Incidents = Angel of Reflection
1. Draw a ray fromthe object into the
mirror
Drawing a ray diagram for a plane mirror
Rule: Angle of Incidents = Angel of Reflection
1. Draw a ray from 2.Draw a normal line atthe object into the the point where the
mirror ray hits the mirror
3.Measure the angle ofincidence
Drawing a ray diagram for a plane mirror
Rule: Angle of Incidents = Angel of Reflection
1. Draw a ray from 2.Draw a normal line at 4. Draw a reflected ray atthe object into the the point where the the same angle
mirror ray hits the mirror
3.Measure the angle ofincidence
Drawing a ray diagram for a plane mirror
Rule: Angle of Incidents = Angel of Reflection
5. Repeat steps 1-4
with a new line
Drawing a ray diagram for a plane mirror
Rule: Angle of Incidents = Angel of Reflection
5. Repeat steps 1-4 6. Use dashed lines to continue the
with a new line reflected rays back behind the mirror
and draw the image where the lines meet (vertex)
Drawing a ray diagram for a plane mirror
Practice drawing diagrams for plane mirrors
Normal
Image Properties
We describe the images mirrors produce using the acronym SPOT
S: Size
P: Position
O: Orientation
T: Type
Image Properties
S: Size Is the image bigger or smaller than the object
P: Position
O: Orientation
T: Type
Image Properties
S: Size Is the image bigger or smaller than the object
P: Position Is the image closer to mirror or further
O: Orientation
T: Type
Image Properties
S: Size Is the image bigger or smaller than the object
P: Position Is the image closer to mirror or further
O: Orientation Is the image inverted or upright
T: Type
v v
Image Properties
S: Size Is the image bigger or smaller than the object
P: Position Is the image closer to mirror or further
O: Orientation Is the image inverted or upright
T: Type Is the image real (in front of the mirror)
or virtual (behind the mirror)
v v
v v
Image Properties for Plane Mirrors
S: Same size
P: Same distance
O: Upright
T: Virtual
Drawing a ray diagram for a curved mirror
Convex and concave mirror diagrams have some different parts than a plane mirror diagram
Principle axis: line drawn at right angle to the centre of the mirror Principle
Axis 2F F
F/ Focal Point : Point on the principal axis, halfway between the mirror and the centre
of the circle created by the mirror
2F: 2 times the focal distance, found at thecentre of the circle created by the mirror
Drawing a ray diagram for a curved mirror
Rule: • Lines going into the mirror parallel to the principle axis, come out through the
focal point (F)
• Lines going in through the focal point, come out parallel
2F Fv v
Drawing a ray diagram for a convex mirror
Rule: In through F out parallel, in parallel, out through F
1. Draw a ray from theobject into the mirror
Drawing a ray diagram for a convex mirror
Rule: In through F out parallel, in parallel, out through F
1. Draw a ray from the 2. Draw a line from F object into the mirror to the same point &
continue it on pastthe mirror
Drawing a ray diagram for a convex mirror
Rule: In through F out parallel, in parallel, out through F
1. Draw a ray from the 2. Draw a line from F 3. Draw a ray from the object object into the mirror to the same point & through the mirror as if to
continue it on past go through Fthe mirror 4. Draw a reflected ray coming
back parallel to the axis
Drawing a ray diagram for a convex mirror
Rule: In through F out parallel, in parallel, out through F
5. Continue the reflected ray back behind the mirror and draw theimage where the lines meet
Image Properties of Convex Mirror
S: Smaller
P: Closer
O: Upright
T: Virtual
Drawing a ray diagram for a concave mirror
Rule: In through F out parallel, in parallel out through F
1. Draw a ray from the object into the mirror parallel to the principle axis
v v
Drawing a ray diagram for a concave mirror
Rule: In through F out parallel, in parallel out through F
1. Draw a ray from the 2. Draw a reflected rayobject into the mirror from that point andparallel to the principle axis through F
v v v v
Drawing a ray diagram for a concave mirror
Rule: In through F out parallel, in parallel out through F
3. Draw a new ray passingthrough F into the mirror
v v
Drawing a ray diagram for a concave mirror
Rule: In through F out parallel, in parallel out through F
3. Draw a new ray passing 4. Draw a reflected ray through F into the mirror coming back parallel
v v v v
Drawing a ray diagram for a concave mirror
Rule: In through F out parallel, in parallel out through F
3. Draw a new ray passing 4. Draw a reflected ray 5. Draw the image where through F into the mirror coming back parallel the reflected rays cross
v v v vv v
Drawing a ray diagram for a concave mirror
Rule: In through F out parallel, in parallel out through F
Drawing a ray diagram for a concave mirror
Rule: In through F out parallel, in parallel out through F
Drawing a ray diagram for a concave mirror
Rule: In through F out parallel, in parallel out through F
Drawing a ray diagram for a concave mirror
Rule: In through F out parallel, in parallel out through F
Drawing a ray diagram for a concave mirror
Rule: In through F out parallel, in parallel out through F
Drawing a ray diagram for a concave mirror
Rule: In through F out parallel, in parallel out through F
Drawing a ray diagram for a concave mirror
Rule: In through F out parallel, in parallel out through F
Image Properties of Convex Mirror
v v v v
1st Example 2nd Example
For concave mirrors image properties depend on how close the object is to the mirror
Image Properties of Convex Mirror
v v v vv v
Behind 2F Between 2F & F In front of F
S -smaller -larger -larger
P -closer -further -further
O -inverted -inverted -upright
T -real -real -virtual
Modeling Light
http://studyjams.scholastic.com/studyjams/jams/science/energy-light-sound/light-absorb-reflect-refract.htm
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