Chapter 7:Understanding Light Topic 7.1: What is Light? Topic 7.2: Reflecting on Reflections Topic...
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Transcript of Chapter 7:Understanding Light Topic 7.1: What is Light? Topic 7.2: Reflecting on Reflections Topic...
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Chapter 7:Understanding Light
Topic 7.1: What is Light?Topic 7.2: Reflecting on
ReflectionsTopic 7.3:Refraction
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Topic: What is Light?A.The First Property of
Light Light is a form
of energy. There are natural
light sources: sun,fire,stars.
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A.The First Property of Light:
Energy can change forms- from natural to artificial.
Ex. Solar to thermal. Ex. Solar to chemical.
Ex. Solar to electrical
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A. Light: cont’d
Artificial light sources: light bulb, match (chemical), a flashlight (electrical)
Thomas Edison (1847-1931)
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B. Sources of Light:1. Incandescent
Incandescent light source: they are so hot they glow.glow. Ex. Light bulbs.
Electrical energy is converted into 95% thermal energy and 5% light energy
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2. Luminescent
Luminescent light: does not need to be hot to create light.
The following, (a)-(d), are all types of luminescent light sources.
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a) Fluorescent light:
Ex. Fluorescent light bulb. Advantage: does not waste energy as heat
(is more energy efficient.) Disadvantage: Filled with mercury (Hg) and
phosphorus (P) , both toxic chemicals
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b) Phosphorescent light:
Ex. Glow in the dark items.
Particles absorb light (radiant) NRG and store it for a time.
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c) Chemiluminescent light source:
Ex. Glow sticks
Light energy released from a reaction between two chemicals.
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d) Bioluminescent light Source:
Ex. Fire flies Chemical
reactions in a living organism provide energy for light.
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Microscopic organism- white spot on the left is the bioluminescence
Bioluminescent mushrooms
Examples of bioluminescence
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C. Watt
The Watt: is the unit of electrical power(W). It indicates the rate at which energy is consumed.
1000 watts= a kilowatt (kW)
Kilowatt-hour is the amount of electrical NRG used in one hour.(kW•h)James Watt (1736-
1819)
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Homework:
BLM7-1BLM 7-2BLM 7-5
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D. Second Basic Property of Light:
Light travels in a straight line.
A ray diagram is used to show the direction in which light is traveling.
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D. Light travels in a straight line
Sun rays through clouds, and shining down into a gorge.
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D. Light travels in a straight line.
Light travels in a straight line until the light strikes an object or material.
The material can be opaque: that is not let any light pass through it.
Ex. wood, metal.
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D. Light travels in a straight line
The material can be translucent: Some light passes through it and it is scattered.
Ex. Frosted glass, wax paper, stained glass.
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D. Light travels in a straight line.
The material can be transparent: All light passes through freely.
Ex. Glass.
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Homework:
BLM 7-8 P.215 #1-4, 6, 7
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Topic 7-2: Reflecting on Reflections
Reflection occurs when light bounces off a surface.
If the surface is smooth, a clear image is produced.
If the surface is rough, a diffuse reflection results.
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A. Laws of Reflection
First Law of Reflection:
The Angle of incidence
is equal to the angle of
reflection.
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A. Laws of Reflection
Second Law of reflection:
The incident ray, thereflected ray and
thenormal are all in thesame plane. This supports the
second basic property of light.
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B. Optical Illusion
Optical illusions fool our brain into making false conclusions.
And they’re lots of fun!
Man playing a horn or silhouette of a woman?
Wine glass or 2 people?
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C. Predictable Behavior of Light
Light rays will either be : Absorbed Reflected Refracted
Reflection: Occurs when light hits a smooth shiny surface and “bounces” off. EX. mirror
“Smooth as glass…”
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C. Predictable Behavior-Reflection
All of the light that reaches a plane(flat) mirror is reflected.
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C. Predictable Behavior-Reflection
This will produce a clear image that is: Upright Same size Same shape Virtual- looks like it is
at the same distance behind the mirror as the actual object is in front of the mirror.
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C. Predictable Behavior-Reflection
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C. Predictable Behavior-Reflection
Any smooth shiny surface will reflect some light rays and images can be seen.
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C. Predictable Behavior-Reflection
Very cool…
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Homework:
P.215 #1-4, 6, 7 BLM 7-8 ,7-10, 7-11, 7-12aq Lab- next class YOU NEED A PROTRACTOR FOR
THIS UNIT.
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Topic 7-3: Refraction
Light travels straight and fast.
The speed of light in air is 300,000 km/s.
Light rays travel more slowly through H2O, glass, etc.
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Refraction
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Topic 7-3: Refraction
Light from the sun takes about 8 minutes to reach the earth!
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Refraction: cont’d
Rainbows are an example of refraction.
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Refraction: cont’d
Light slows down as it travels through a denser medium.
The Normal is perpendicular to the edge of the material.
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Refraction
Light rays bend as they move from materials of differing densities.
Ex. Air to glass Some light rays
are reflected, some refract.
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Refraction: cont’d
Relationship with respect to density:
As density increases, the angle of refraction decreases.
An inverse relationship.
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Refraction: cont’d
When light travels through a less dense medium, the light ray will bend away from the Normal.
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Refraction: cont’d
The fish sees the bird in a refracted position.
Water to air: density decreases;angle of refraction increases.
Bends away from the Normal
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Homework
BLM 7-14, 7-18 Draw diagram
7.23 (p. 230) Draw table 7.1
(p.231)