1. Ray Model of Light Explains that light travel in straight lines
Sources of light: sun, stars, fire, electrical storms, fireflies, jellyfish – bioluminescence, flaghlights, lamps, neon signs
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2. This model is known as the Particle Model of Light.
5.1 The Ray Model of Light
Newton thought of light as extremely small particles that traveled in a straight line until they entered an eye, where they were absorbed to make an image.
This model is known as the Particle Model of Light.
Parts of this model are still used today.
Some properties of light are best described by considering light as a wave, such as the use of wavelength and frequency to account for the different colours of light.
Issac Newton believed that light is a stream of fast-moving tiny particles that traveled in a straight line until they reached the eye where they were absorbed to make an image.
See page 168
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3. 5.1 The Ray Model of Light
The Ray Model of Light is more simplified, it uses a straight line, or ray, to show the direction the light wave is traveling.
Both models describe some properties of light but neither one describes of light’s properties.
Some properties of light are best described by considering light as a wave, such as the use of wavelength and frequency to account for the different colours of light.
Issac Newton believed that light is a stream of fast-moving tiny particles that traveled in a straight line until they reached the eye where they were absorbed to make an image.
See page 168
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4. Different materials can either transmit, absorb, or reflect light.
Light and Matter:
Different materials can either transmit, absorb, or reflect light.
See pages
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5. Transparent materials allow light to pass through freely.
Transparent Objects
Transparent materials allow light to pass through freely.
They transmit light.
Eg. Clear plastic bags
See pages
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6. Some light absorbed and/or reflected
Translucent
Translucent materials lets most light through but scatters the light leaving.
Some light absorbed and/or reflected
Eg. Frosted glass, lampshade, wax paper.
Often used in bathrooms. Why would we want this? Allow light in but maintain privacy.
See pages
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7. Opaque materials absorb and reflect light
Opaque materials prevent light from passing through.
They absorb and reflect light.
Wood, metal, cardboard, eyelids, books, aluminum foil
Leaves dark shadow
What is a shadow? What determines the size/length?
See pages
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8. A shadow is created when an opaque object absorbs light rays.
Shadows
A shadow is created when an opaque object absorbs light rays.
Shadows demonstrate that light travels in straight lines.
A ray diagram shows how the distance from the light source affects the size of the shadow an object makes.
See page 171
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9. Shadow sized depends on distance f rom light source
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10. Shadows s
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11. Check your understanding
How is an opaque material different from a translucent material?
How is a translucent material different from a transparent material?
Is a glass of water with red food colouring in it translucent or transparent?
What is the relationship between the size of the shadow and the distance of the object from the light source?
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12. Reflection is when light bounces off of an object.
Light Can Be Reflected
Reflection is when light bounces off of an object.
To act like a mirror, the surface must be smooth.
The incoming ray of light is called the incident ray.
The ray that bounces off the surface is called the reflected ray.
Reflected ray
Incident ray
Flat tin foil vs crumpled tin foil
See page 172
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13. The normal is an imaginary line perpendicular to the surface.
The Law of Reflection
The normal is an imaginary line perpendicular to the surface.
The angle of incidence is measured from the normal to the incident ray.
The angle of reflection is measured from the normal to the reflected ray.
The angle of reflection (r) equals the angle of incidence. (i)
See page 173
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14. The angle of reflection (r) equals the angle of incidence (i).
The Laws of Reflection
The angle of reflection (r) equals the angle of incidence (i).
The reflected ray and the incident ray are on opposite sides of the normal.
The incident ray, the normal, and the reflected ray lie on the same plane (flat surface).
See page 173
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15. Law of Reflection
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16. Check your understanding
What is the law of Reflection?
Why does a white page not reflect like a mirror?
What is the difference between the incident ray and the reflected ray?
What point does the normal intersect?
What does the angle of incidence always equal?
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17. Activity 5-5 p178
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18. This change in speed causes the light to change direction.
Light Can Be Refracted
When light travels from one transparent medium to another of a different density, it changes speed.
This change in speed causes the light to change direction.
The bending of light, due to a change in speed, is called refraction.
See page 174
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19. Once inside the glass the light rays move in a straight line.
Light Can Be Refracted
When light rays move from air into glass, they slow down and change direction because the glass is denser than air.
Once inside the glass the light rays move in a straight line.
What will happen if the light rays
leave the glass and move back into
air, which is less dense?
See page 174
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20. They will travel faster and change direction again (refract)
Light Can Be Refracted
They will travel faster and change direction again (refract)
See page 174
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21. Light Can Be Refracted
The angle of refraction is measured from the refracted ray to the normal.
See page 174
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22. Refraction of Light in Water
Objects in water appear in a different location than they actually are. This is due to the refraction of the light.
See page 175
Take the Section 5.1 Quiz
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23. Refraction of Light in Air
Air at different temperatures has different densities.
Warm air is less dense than cold air.
Light refracts when it passes through air at different temperatures. (mirage)
See page 175
Take the Section 5.1 Quiz
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24. Refraction of Light in Air
The “pools of water” you see on the highway on a hot day is due to the air closer to the ground is hotter and less dense than air higher up.
Light from the sky directed at the ground is bent upward as it enters the less dense air.
The “pools of water” are actually images of the sky refracted by warm air near the ground.
See page 175
Take the Section 5.1 Quiz
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25. Check your understanding
Why does a white page not reflect like a mirror?
What is the difference between the incident ray and the reflected ray?
What point does the normal intersect?
What does the angle of incidence always equal?
What happens with light rays travel from water into air?
Why do objects underwater seem closer to the surface than they are?
Why does the highway ahead of you sometimes look wet when it is actually dry?
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26. Homework Read pages 168-173 Answer CYU p181 # 1, 2, 3, 4, 6, 9
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