Light
Lesson 2
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Questions from last class
1. What is Light?
Light is the form of
energy that we can see
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Questions from last class
2. What are sources of Natural Light and
why are they called “natural light”?
They are called “natural light” because
they are not made by humans
Examples: the sun and other stars, Fire, Sparks,
firefly, angler fish, northern lights, lightning
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4
Questions from last class
3. How does the sun create light?
Nuclear fusion: When hydrogen atoms
fuse(combine) together under very large heat
and gravity in the sun they create helium
particles. During this process mass is lost and
turned into energy(heat and light) because
E=mc
2
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Questions from last class
4. List at least 5 ways you’ve used light today?
(include situations using reflection)
Traffic lights
Tv
Computer
lighting your room
looking in a mirror
cellphone
Calculator
food you ate
digital clock
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Sources of Light
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Candle
Observations:
brightness, temperature, colour, etc
how do you think the light is being produced?
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Glow Sticks
Observations:
brightness, temperature, colour, etc
how do you think the light is being produced?
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Regular lightbulb
Observations:
brightness, temperature, colour, etc
how do you think the light is being produced?
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Spiral Bulb
Observations:
brightness, temperature, colour, etc
how do you think the light is being produced?
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glow-in-the-dark beads
Observations:
brightness, temperature, colour, etc
how do you think the light is being produced?
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Glowing Living things
What do these all have in
common?
What does the light look most like?
(think about the colour)
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Incandescent Source
An object that can be heated to
such a high temperature that it
emits visible light.
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Luminescent Source
An object that gives off light
without heat
Split into 4 groups....
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Fluorescent Source
An electric current in a gas filled
tube causes mercury vapour to
produce ultraviolet light that then
causes a phosphor coating on the
inside of the bulb to glow.
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Phosphorescent Source
Light energy is absorbed by
certain particles that can store
this energy for a while. The
stored energy is later released
as visible light.
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Chemiluminescent Source
A chemical reaction
between substances
gives off light without
creating heat.
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Bioluminescent Source
A form of
chemiluminescence
that occurs in living
organisms.
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Lightbulb
Incandescent Source
Electricity flows through the
filaments creating a lot of heat
and light
Electrical energy → Thermal energy → Visible light energy
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Electricity
Moving electrons
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Candle
Incandescent Source
Wick burns
with fuel from
wax (which is
made of oil)
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Glowsticks
Luminescent
Chemiluminescent
A breakable barrier
separates two liquids.
Bending the stick
causes the barrier to
break. The liquids mix
and cause a chemical
reaction that releases
glowing light.
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Spiral Bulb
Luminous Source
Fluorescent Source
CFL- Compact Fluorescent Source
Electrical energy → Energy absorbed by
mercury particles → Mercury gets excited
→ releases high energy UV rays → UV
rays absorbed by phosphor coating →
Visible light emitted by phosphor
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Ultra Violet Light (UV)
Light that has so much
energy that humans
can’t see it
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Ultra Violet Light (UV)
Why does white glow when you go
glow bowling?!?!
Particles in detergent
absorb UV rays and emit
visible light
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Florescent Colours
this?
Why does this
look
brighter
than
Particles in Neon dye
absorb UV rays and
then emit light
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Please recycle CFLs
These bulbs are filled
with mercury- a toxic
chemical
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Glow-Beads
Luminous
Phosphorescent
Light is stored by
particular particles in
the beads then
released even after the
original light source is
gone
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Glowing Animals
Luminous
Bioluminescent
Light is Created by
living things due to a
chemical reaction
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Light Concept Map
Read pages 207-209
Then create a concept map to show the relationships among
the following terms:
visible light, incandescent, luminescent, fluorescent,
phosphorescent, chemiluminescent, bioluminescent, hot, not
hot, candlelight, glow stick,
spiral lightbulb(fluorescent bulb), normal lightbulb,
glow-in-the-dark beads, and firefly
visible light
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Questions
Read pages 207-209
1. What are UV rays and why can’t we see them?
2. Why do some white shirts glow under UV light and
some don’t?
3. Explain how Regular Bulbs, Fluorescent bulbs, glow
sticks and glow beads create light.
4. Why are Fluorescent bulbs more energy efficient than
Incandescent bulbs?
5 .What is the main difference between fluorescence and
phosphorescence.
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