flat mirrors and the law of reflection. types of reflection there are two main ways in which light...
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Flat Mirrors
And the Law of Reflection
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Types of Reflection
• There are two main ways in which light reflects.
• Diffuse Reflection is caused by light hitting a rough surface and being reflected in many different directions.
• Specular Reflection is caused by light hitting a smooth surface and being reflected in only one direction.
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Mirrors
• Mirrors are examples of Specular reflectors.
• Only objects that reflect light this way allow images to be “reflected”.
• Examples: Mirrors, calm water, shiny metal.
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Describing Reflected Light
• When light hits a mirror, we use angles to predict the path of the light beam when it is reflected.
• The angle of incidence, ө1, is the angle the light makes normal to the mirror.
ө1
Normal Line
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Describing Reflected Light
• When the light beam reflects, it creates a second angle, also measured from the normal.
• How do ө1 and ө2 compare?
ө1 ө2
Normal Line
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Law of Reflection
• Ө1 and Ө2 are always going to be equal.
• We call this relationship the Law of Reflection
• The Law of Reflection states that for a reflected ray of light the angle of incidence (Ө1) and the angle of reflection (Ө2) are equal to each other.
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Taking another look
ө1 ө2
Angle of incidence
Angle of reflection
So, if ө1 = 30°, ө2 = 30°
And if ө1 = 80.2°, then ө2 = 80.2°
And so on and so on…
Normal Line
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Ray Diagrams Practice Problems
• When constructing a ray diagram, all diagrams must have:
• A mirror
• Normal Line
• Light Ray
• Angle of incidence
• Angle of reflection
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Ray Diagrams Example 1
• When looking in a mirror, you can see the reflection of your feet. Draw a ray diagram of a light beam from your shoes to your eye.
Mirror
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Ray Diagrams Example 1
ӨӨ
Angle of incidence
Angle of reflection
Mirror
Normal Line
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Ray Diagram Example 2
• Mirrors are sometimes used in parking lots as a safety feature. Draw a ray diagram showing how the mirror lets you see around corners. Include a ray of incidence of 45˚.
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Ray Diagram Example 2
45˚
45˚
Normal Line
Angle of Incidence
Angle of Reflection
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Ray Diagram Example 3
• Construct a ray diagram showing a ray of light bouncing off the rear view mirror of your car, enabling you to see someone sitting on the passenger side front seat.
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Ray Diagram Example 3
Normal
Ө Ө
Angle of Angle of
Reflection Incidence
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How do we use the Law of Reflection??
• The Law of Reflection can be used to find out many different things.
ө ө
Note: Since Ө1 = Ө2, lets
just call them both Ө to keep
it simple.
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Using the Law in ray diagrams
• A man stands 2 m tall at eye level looking at his shoes in a full length mirror. Construct a ray diagram of the light traveling from his shoes to his eyes.
ө
ө
Now, if we know the angle of incidence, we can calculate how far away he is from the mirror using Trigonometry.
2 m
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The angle of incidence = 60°
ө= 60°2 m
1 m
1 mx
• To solve for the distance x we use the definition of tanӨ.
• tanӨ = Opposite/ Adjacent• tan(60°)= 1m / x • x= 1m / tan(60˚) So x = .578m.
Reminder:
SinӨ = Opp / Hyp
CosӨ = Adj / Hyp
TanӨ = Opp / Adj
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Let’s practice a few more…