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LIGHT ENERGY &
ITS SOURCES
Section 10.1
IN GROUPS
Discuss the following and are ready to give answers when prompted:
1.
What are the sources of light?
2.
How does a light bulb work?
3.
What does luminous and non-luminous mean?
GIVES OFF LIGHT (EMITS)
4.
Electricity passes through the filament
and its starts to get hot and glows.
REFLECTS LIGHT
How is a shadow formed?
A SOLID OBJECTS BLOCK THE LIGHT
5.
What does transparent, translucent and opaque mean?
Can see through
can see some light
light cant get through
LIGHT
• Light is a form of energy that can be detected by the human eye
• Light energy comes from both natural and artificial sources
• Light travels directly from a luminous source (object that emit light) or
indirectly from a non-luminous source (object reflects light) to your eyes
INCANDESCENCE
• Emitting light because of high temperatures
• Kerosene lamp uses chemical energy to
transform into heat and light.
• electricity passes through a tungsten wire
in a bulb making it so hot that it glows
Electrical energy → light energy + thermal energy
• Inefficient - since much of the
input energy becomes
thermal (heat) energy
LUMINESCENT
•
an emission of light by a substance not resulting from heat
ELECTRIC DISCHARGE
• Electric discharge is the
process of emitting light
because of electricity
passing through a gas
• Examples: Lightning, neon signs
PHOSPHORESCENCE
• Materials called phosphors
store light energy and
release it again as light
energy
• Phosphorescence is the
process of emitting light for
a short time after receiving
energy from another source
FLUORESCENCE
Fluorescence is the process of
emitting light while receiving
energy from another source
Ex. Fluorescent light tubes
Fluorescence is a combination
of two different light sources,
electric discharge and
phosphorescence
• Electricity passes along the tube and causes
particles of mercury vapour to emit invisible
ultraviolet (UV) energy.
• The UV energy is absorbed by the phosphor
coating on the inside of the tube, which then
emits light energy.
CHEMILUMINESCENCE
• Chemiluminescence is the process of changing chemical energy
into light energy with little or no change in temperature
BIOLUMINESCENCE
Bioluminescence is when chemiluminescence is used in living things
Visible Light
Luminescent
(emits light without heat)
Incandescent
(emit light because of
heat)
Phosphorescent
Candlelight
Glow-in-dark
stickers
Chemiluminescent
Electric
Discharge
Bioluminescent
neon signs
Fluorescent
firefly
glow sticks
fluorescent bulbs
Activity: Create a concept
map of the different sources
of light breaking them down
from visible light to
examples.
SOURCES OF LIGHT
What factors should be considered when choosing a light source?
• Brightness
• Location
• Attractiveness
• Cost
• Efficiency (how well the light source
transforms input energy into light
energy)
Project: Create an advertisement
promoting a source of light