Properties of Light

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Properties of Light
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What can you see?
NOTES
You can only see things that are either

• luminous (emitting light)
• illuminated (reflecting light)

In a perfectly dark room, there is no light to be
emitted or reflected.
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Seven Properties of Light

• Light travels very fast.
• Light has a dual nature.
• Light travels in straight lines.
• Light can vary in intensity.
• Light interacts with matter.
• Light is comprised of many colors.
• Light carries energy and information.

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Electromagnetic Waves

• Light is made of electromagnetic waves.
• Take a prism and break up white light into a
  rainbow like band of colors. These are all in the
  visible spectrum.
• Red, orange, yellow, green, blue, indigo and
  violet.
• ROY G BIV

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Electromagnetic Waves

• The spectrum also includes non-visible
  electromagnetic waves, such as x-rays,
  microwaves, radio waves, and radiation.
• all have similar properties.

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Electromagnetic Waves

• Electromagnetic waves vary depending on frequency
  and wavelength
• All electromagnetic waves move at the speed of
  light

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1. Light Travels Very Fast
NOTES
Nothing travels faster than light! Light
travels three hundred MILLION meters each second.
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Electromagnetic Waves

• We will use 3.00 X 108 m/s as the speed of light,
  c.
• The wave speed equation is
• c f?
• Speed of light frequency X wavelength

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Sample Problem

• The AM radio band extends from 5.4 X 105 Hz to
  1.7 X 106 Hz. What are the longest and shortest
  wavelengths in this frequency range?
• f 1 5.4 x 105 Hz f 2 1.7 x 106 Hz
• c 3.0 x 108 m/s
• c f?
• ? c/ f
• ?1 5.6 x 102 m
• ?2 1.8 x 102m

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2. Light Has a Dual Nature
NOTES
Light can behave as waves, or as particles called
photons.
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3. Light Travels in Straight Lines
NOTES
When unimpeded, light travels along linear paths.
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How do shadows form?
Light rays are represented as straight paths.
When they are blocked by solid objects, shadows
are formed.
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Shadows vary
Objects close to the screen form sharp shadows.
Object far from the screen form blurry shadows.
Objects in front of large light sources form
blurry shadows.
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4. Light Varies in Intensity
NOTES
 
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4. Light Varies in Intensity

• The intensity of light from a source depends on
  how close you are to it.
• When you are close to the source, the light is
  more intense.
• When you are far from the source, the light is
  less intense.

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4. Light Varies in Intensity
NOTES
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Test your knowledge
The light intensity 1.0 meter from a 100 Watt
light bulb is 8.0 W/m2. What is the light
intensity 2.0 meters from the bulb?
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Test your knowledge

• The light intensity 1.0 meter from a 100 Watt
  light bulb is 8.0 W/m2.
• What is the light intensity 2.0 meters from the
  bulb?
• ¼ as much, so 2.0 W/m2
• What is the light intensity 50 cm from the bulb?
• 4 times as much, so 32 W/m2

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5. Light Interacts with Matter
NOTES
Light can change speed and direction when it
interacts with matter. Light reflects off a
mirror and refracts as it passes through from air
to glass to water.
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6. Light is Comprised
NOTES
of Many Colors
White light is composed of many colors. It can
be dispersed (separated) using a prism.
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What kind of light can we see?
There are sounds that are too high or low
frequency for our ears to hear. There is also
light that is too high or low frequency for our
eyes to see.
The light we can see is called visible light. It
includes all the colors of the rainbow. Can you
name any of the types of light that we cant see?
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There is light we cant see
Most of the electromagnetic spectrum is not
visible to us. We have many uses for these
invisible parts of the spectrum.
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1. Light Carries Energy and Information

NOTES
We use light to communicate through AM/FM radios,
mobile phones, and fiber optic cables.
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Assessment

• 1. Which of these is NOT a property of light?
• Light travels very fast.
• Light has constant intensity.
• Light carries energy and information.
• Light exhibits both wave and particle behavior.

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Assessment

• 1. Which of these is NOT a property of light?
• Light travels very fast.
• Light has constant intensity.
• Light carries energy and information.
• Light exhibits both wave and particle behavior.

• Light travels in straight lines. Can you name
  two ways to get a light beam to change direction?

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Assessment

• 1. Which of these is NOT a property of light?
• Light travels very fast.
• Light has constant intensity.
• Light carries energy and information.
• Light exhibits both wave and particle behavior.

• Light travels in straight lines. Can you name
  two ways to get a light beam to change direction?
• answer reflection and refraction

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Assessment

• Name at least three types of radiation that are
  part of the electromagnetic spectrum but are NOT
  visible.

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Assessment

• Name at least three types of radiation that are
  part of the electromagnetic spectrum but are NOT
  visible.
• correct answers include gamma rays,
  x-rays, ultraviolet light, infrared light, and
  radio waves
• 4. Why is it that we can see the Moon?
• It is luminous (emits light).
• It is illuminated (reflects light from another
  source).

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Assessment

• Name at least three types of radiation that are
  part of the electromagnetic spectrum but are NOT
  visible.
• correct answers include gamma rays,
  x-rays, ultraviolet light, infrared light, and
  radio waves
• 4. Why is it that we can see the Moon?
• It is luminous (emits light).
• It is illuminated (reflects light from another
  source).