The Physics of Light by Mr' Schneider, Rm 24

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The Physics of Light by Mr. Schneider, Rm 24
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What Is Light?

• In this Powerpoint presentation
• Properties of light
• Reflection - Mirrors
• Refraction - Lenses
• Colors (next lecture)

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Part 1 Properties of Light

• Light travels in straight lines

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• Light travels VERY FAST about 300,000
  kilometers per second.

At this speed light could travel the equivalent
of 8 times around the world in one second!
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• Light travels much faster than sound. For example

• Thunder and lightning start at the same time, but
  we will see the lightning first.

• 2) When a starting pistol is fired we see the
  smoke first and then hear the bang.

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• We see things because they reflect light into our
  eyes

Homework
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• Luminous and non-luminous objects

A luminous object is one that produces light. A
non-luminous object is one that reflects light.
Luminous objects
Reflectors
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• Shadows

Shadows are places where light is blocked
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Light is a form of energy calledElectromagnet
ic Radiation- Em Radiation comes from the sun
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Properties of Light summary

• Light travels in straight lines
• Light travels much faster than sound
• We see things because they reflect light into our
  eyes
• Shadows are formed when light is blocked by an
  object
• Visible light is part of the electromagnetic
  spectrum

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Part 2 - Reflection and Mirrors
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Regular vs. Diffuse Reflection

• Smooth, shiny surfaces have a regular reflection

Rough, dull surfaces have a diffuse
reflection. Diffuse reflection is when light is
scattered in different directions
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Using mirrors

• Two examples

2) A car headlight
1) A periscope
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Types of Mirrors Plane, Concave, Convex
Plane mirrors are flat and make virtual images.
The images is virtual because the light rays
do not come from the image, they only appear to
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Concave Mirrors are curved inward - just
remember, you go in to a cave, and in to a
concave mirror!
Virtual images
Real image
The mirage box on Mr. Ss desk is made of two
concave mirrors. Images of concave mirrors can
be virtual or real!
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Convex mirrors are mirrors that curve outward
Convex mirrors are used for security purposes, in
cars etc. They allow us to see a wide view. The
images they make are virtual
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Review of Reflection

• Two types of reflection, regular and diffuse
• Mirrors come in 3 types plane, convex and
  concave. Each has a distinct shape and use.
• Mirrors can make virtual images or real images
  depending on their type
• Virtual images - light rays do not meet and the
  image is always upright or right-side-up
• Real images - always upside down and are formed
  when light rays actually meet

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Refraction
Refraction is when waves ____ __ or slow down due
to traveling in a different _________. A medium
is something that light waves will travel
through. When a ruler is placed in water it
looks like the diagram in the next slide. In the
diagram the light rays are slowed down by the
water and are _____, causing the ruler to look
bent at the surface. The two mediums in this
example are ______ and _______. Words speed up,
water, air, bent, medium
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The degree that light bends when it enters a new
medium is called the index of refraction
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(No Transcript)
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Lenses work because of refraction! Light is bent
as it enters a new medium, glass!
Convex lenses

• Thicker in middle, thin on edges
• Light rays meet to form a focal point
• Makes real images since light rays come together
  from a light source, but can also make virtual
  images (center picture)
• Used in cameras, telescopes, human eye

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Concave Lenses

• Concave lenses are thin in the middle and thicker
  on the edges
• Since light rays never meet with this lens, they
  make virtual images only
• Used in cameras telescopes to correct spherical
  aberation, and also eyeglasses

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Review of Refraction

• Light rays slow down when they enter a new medium
• Refraction can cause light rays to change their
  direction
• All transparent materials have their own index
  of refraction
• Light is refracted when it passes through lenses
  and this creates images

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Color

• White light is not a single color it is made up
  of a mixture of the seven colors of the rainbow.

We can demonstrate this by splitting white light
with a prism This is how rainbows are formed
sunlight is split up by raindrops.
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The colors of the rainbow

• Red
• Orange
• Yellow
• Green
• Blue
• Indigo
• Violet

Just remember ROY G. BIV
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Adding colors of light

• White light can be split up to make separate
  colors. These colors can be added together
  again.
• The primary colors of light are red, blue and
  green

Adding blue and red makes magenta (purple)
Adding blue and green makes cyan (light blue)
Adding all three makes white again
Adding red and green makes yellow
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Seeing color

• The color an object appears depends on the colors
  of light it reflects.

For example, a red book only reflects red light
White light
Only red light is reflected
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A pair of purple trousers would reflect purple
light (and red and blue, as purple is made up
of red and blue)
Purple light
A white hat would reflect all seven colors
White light
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Using colored light

• If we look at a colored object in colored light
  we see something different. For example,
  consider the color of this outfit

Shirt looks red
White light
Shorts look blue
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• In different colors of light this shirt would
  look different

Red light
Shirt looks red
Shorts look black
Shirt looks black
Blue light
Shorts look blue
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Some further examples
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Using filters

• Filters can be used to block out different
  colours of light

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Investigating filters
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Red
White
Blue
Green
Magenta
Yellow
Cyan
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Part 2 - Reflection and Mirrors

• Reflection from a mirror

Normal
Reflected ray
Incident ray
Angle of reflection
Angle of incidence
Mirror
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• The Law of Reflection

Angle of incidence Angle of reflection
In other words, light gets reflected from a
surface at ____ _____ angle it hits it.
The same !!!
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• Brain Pop Movie on Color

Brain Pop Movie on Color! Enjoy it!
View the movie on Color from Brain Pop. Then
take the quiz at the end of the movie. How did
you do?