11.2
How Is Light Produced?
OVERALL EXPECTATIONS
• identify and describe a variety of careers related to the fields of science
under study, and identify scientists, including Canadians, who have made
contributions to those fields
• evaluate the effectiveness of technological devices and procedures to make use
of light, and assess their social benefits
• investigate, through inquiry, the properties of light, and predict its behaviour,
particularly with respect to reflection in plane and curved mirrors and
refraction in converging lenses
• demonstrate an understanding of various characteristics and properties of
light, particularly with respect to reflection in mirrors and reflection and
refraction in lenses
SPECIFIC EXPECTATIONS
Time
45–60 min
Vocabulary
• luminous
• non-luminous
• incandescence
• electric discharge
• phosphorescence
• fluorescence
• chemiluminescence
• bioluminescence
• triboluminescence
• light-emitting diode (LED)
• semiconductor
Skills
Career Exploration
• identify scientists, including Canadians, who have made a contribution to the
fields of science under study
Predicting
Controlling variables
Observing
Relating Science to Technology, Society, and the Environment
Equipment and Materials
• analyze a technological device that uses properties of light and explain how it
has enhanced society
Developing Skills of Investigation and Communication
• use appropriate terminology related to light and optics
Understanding Basic Concepts
• describe and explain various types of light emissions
KEY CONCEPTS
• Light is produced by natural and artificial sources.
per class:
• freezer
per group:
• a light stick
• two large beakers or
transparent
plastic containers
• ice cubes
• tap water
• large mirror
per student:
• two sugar cubes
• a wintergreen-flavoured
hard candy
EVIDENCE OF LEARNING
Assessment Resources
Look for evidence that students can
Assessment Rubric 2:
Thinking and Investigation
Assessment Summary 2:
Thinking and Investigation
• identify and explain the difference between luminous and non-luminous sources
• identify and explain how light is produced by natural and artificial sources
• identify light from incandescence, electric discharge, phosphorescence, fluorescence,
chemiluminescence, bioluminescence, triboluminescence, and LEDs
SCIENCE BACKGROUND
Light Sources
enough, the filament gives off light.
In other words, thermal energy is
converted to light energy. Note that
an incandescent light bulb is not very
efficient. Most of the energy in the
filament is lost as infrared radiation,
which is not a form of visible light.
BLM 0.0-3 Compare and
Contrast Chart
BLM 0.0-8 Term Box
Skills Handbook 3. Scientific
Inquiry Skills
Skills Handbook 4. Research
Skills
Science Perspectives 10
website www.nelson.com
/scienceperspectives/10
▼
• In an incandescent light bulb, electric
current is run through a highresistance filament. The filament
resists the flow of electrons, and some
of the electrical energy is converted
into thermal energy. When it gets hot
▼
Other Program Resources
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Related Resources
• Light produced by electric discharge
also relies on the conversion of
electrical energy to light energy, but it
produces little thermal energy. Electric
discharge in a gas-filled bulb (neon,
argon, mercury) starts with applying
a voltage across the sealed tube. For
neon, a fairly small voltage will excite
the atoms and cause them to emit
light.
Levy, Joel. Really Useful:
the origins of everyday
things. Firefly Books,
2002.
Dulken, Stephen. Inventing
the 19th Century: 100
Inventions that Shaped
the Victorian Age, From
Aspirin to the Zeppelin.
NYU Press, 2006.
• Phosphorescence and fluorescence rely
on invisible ultraviolet light to excite
substances that emit visible light. Note
that with phosphorescence, there is a
time delay before the substance emits
light; with fluorescence, the emission
of light is more immediate.
Science Perspectives 10
ExamView® Test Bank
Science Perspectives 10
Teacher eSource SUITE
Upgrade
Science Perspectives 10
website www.nelson.com
/scienceperspectives/10
• Chemiluminescence and
bioluminescence result from chemical
reactions. Chemiluminescence is used to
produce items used for entertainment
and safety. Bioluminescence is used by
living organisms to protect themselves
from predators, to lure prey, or to
attract mates.
• Triboluminescence is the production
of light when certain crystals are
scratched, crushed, or rubbed.
There does not currently appear
to be any practical application of
triboluminescence.
• Light-emitting diodes (LEDs) use
semiconductors to produce light.
Semiconductors are neither conductors
nor insulators and are used in
LEDs to restrict current flow to one
direction. LEDs produce less heat than
incandescent bulbs and are more
energy efficient. The number of areas
in which LEDs are used is growing
due to recent improvements in the
technology. Uses include Christmas
lights, illuminated signs, and traffic
lights.
TEACHING NOTES
Engage
• In this section, students will be learning about several different ways in which
light is produced. To engage students, provide some examples of objects that
produce light. Before class begins, place several glow-in-the-dark toys in the
classroom. Shut off the classroom lights, and have students observe these
toys (you may have to bring the toys to a darker area of the room). Turn the
lights on and initiate a class discussion by asking, How do these toys produce
light? How is this similar or different from a light bulb or a bolt of lightning?
Tell students that in this section they will learn that phosphorescence is the
phenomenon that causes these objects to glow.
• Before students read the section, have them preview the red headings. Point
out that each heading describes a different way in which light is produced.
Writing Tip
Writing Persuasively
Remind students to make
use of facts when stating
their key points. Remind
them that the statement
“Canadians developed the
electric light bulb before
Thomas Edison did”
represents their opinion
(for this Writing Tip) and
that persuading someone
to that opinion requires
facts.
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Explore and Explain
• Discuss incandescence (page 470) by having students explain what the lights
produced in Figure 1, Figure 2, and Figure 3 have in common. (In each case,
the light is produced by incandescence.) Make sure they understand that in
each case light is produced through heat and have students think of other
examples of incandescence.
• Proceed by talking to students about light from electric discharge. Explain
that “neon lights” is a generic term used to refer to lights using electric
discharge and that, in addition to neon, other gases are used in electric
discharge lights, each producing a different colour of light.
• Go over the information about phosphorescence and fluorescence. Remind
students of the glow-in-the-dark toys used to introduce this section and point
out Figure 8. Ask, What type of light production is associated with glow-in-the-dark
toys? (phosphorescence) How is phosphorescent light produced? (Phosphorescent
material gets excited by ultraviolet light and emits visible light.)
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• Discuss how fluorescent light is produced, making reference to Figure 9
on page 472 of the Student Book. This is a great time to discuss the energy
and cost savings that can be realized by changing incandescent lighting to
fluorescent lighting. Take a poll of students to see how many have CFLs in
their homes. Discuss any differences that students notice in CFLs versus
incandescent lights (e.g., less heat produced, different appearance (colour) of
the light).
• Have students complete Citizen Action: Thinking for the Future, in which
they will examine how changing the type of light they use can reduce their
energy bill and reduce greenhouse gas emissions.
CITIZEN
ACTION
Thinking for the Future
Purpose
• Students will research the how CFLs can be used
to personally reduce contributions to global
warming.
Notes
• As a class, you may wish to develop a letter to
parents related to this activity, as it encourages
students to actually change the lights in their homes
from incandescent to CFL. For students whose lights
have already been changed, have them compare
monthly energy usage prior to the change to the
energy usage after their lights were changed.
Remind students to use quantitative data in their
ad campaigns. Students can visit the Nelson Science
Perspectives 10 Student eSource to learn more
about this activity.
• Introduce the topic of chemiluminescence, the production of light as a direct
by-product of a chemical reaction. Show a glow stick to the class, an example
of chemiluminescence with which most students will be familiar. Save a full
discussion of chemiluminescence until after the Try This activity.
• Have students complete the Try This: Glowing With Light. Here students
will be able to experiment with glow sticks at different temperatures and
compare how much light is produced. They will find out that temperature
affects how much energy an object has.
T RY THIS
GLOWING WITH LIGHT
Skills
• Predicting, Controlling Variables, Observing
Purpose
• Students will relate the temperature of a glow stick
to the amount of light emitted.
Equipment and Materials
• per class: freezer
• per group: a light stick; two large beakers or
transparent containers; ice cubes; tap water
Student Safety
• Tell students that light sticks contain broken glass and
toxic chemicals. Provide a single place for any broken
glow sticks to be disposed, such as a plastic garbage
bag. You might want to check your school’s policy for
disposal of items like these.
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Suggested Answers
A. Sample answer: I predicted that the amount of light
emitted would decrease as the temperature decreased
and would increase as the temperature increased. I
was correct; my observations matched my predictions.
B. The light stick was dimmer when it was cooler and
brighter when it was warmer.
C. Sample answer: The chemicals in the light stick must
react to make light. When they are cold, they do not
react as quickly and produce less light. My classmates
also made the same conclusion.
D. The frozen light stick produced virtually no light, but
when it was warmed up, it once again produced
light. The freezer made the light stick so cold that
the chemicals stopped reacting, but they were able
to react when the light stick was warmed.
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• Further discuss chemiluminescence with the class and introduce
bioluminescence. Explain that both rely on chemical reactions to produce
light, but that bioluminescence is a particular kind of chemiluminescence
that takes place in a living organism. Discuss examples of each:
chemiluminescence (luminol test for the presence of blood), bioluminescence
(firefly)
• Have students complete Try This: Eating Candy For the Sake of Science.
This activity will provide students with a fun way to learn about
triboluminescence and see it first-hand.
T RY THIS
EATING CANDY FOR THE SAKE OF SCIENCE
Skills
• Observing
Purpose
• Students will observe triboluminescence.
Equipment and Materials
• per group: a lab partner or a large mirror
• per student: two sugar cubes; a wintergreenflavoured hard candy
Notes
• Students may work in pairs for this activity; alternatively,
this activity can be done independently at home.
Suggested Answers
A. The sugar cubes produced “sparks” of light when
struck together.
B. The candy also produced “sparks” of light when
bitten.
• Remind students that conductors were studied in Grade 9. Ask a volunteer
to recall and summarize what they remember about conductors for the class
(metals are good conductors, copper is commonly used in household wiring,
resistance depends on material and the cross-section and length of wire).
Explain that a semiconductor only allows current to flow in one direction,
as opposed to two directions for conductors. This is why semiconductors
are used in LEDs. Ask students to explain some of the advantages of LED
light production when compared to incandescent lighting (more energy
efficient, produce less heat).
Extend and Assess
• Lead a class discussion comparing and contrasting the various ways that light
is produced. This will give students a good summary of the section. You may
wish to provide some students with BLM 0.0-3 Compare and Contrast Chart
and have them examine the similarities and differences between light sources
of their choosing.
• Have students complete the Check Your Learning questions on page 476 of
the Student Book.
CHECK
YOUR LEARNING
Suggested Answers
1. Stars are luminous; planets and moons are non-luminous because they only reflect light and do not actually
produce it
2. Most of the electrical energy it uses becomes heat, not visible light.
3. electric discharge
4. Phosphorescent materials turn absorbed UV light into emitted visible light over varying periods of time, but
fluorescent materials do so immediately.
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5. (a) No, they just make clothes “glow” by fluorescence in daylight.
(b) Sample answer: It is unwise to use detergents with additives, because they cause harm to the environment.
This threatens all living organisms.
6. A fluorescent material would not glow if it were illuminated by infrared light. This is because fluorescence requires
ultraviolet light. Infrared light has less energy than ultraviolet light.
7. Chemiluminescence is called “cold light” because it produces light, but virtually no heat.
8. A light stick would be relatively safe in an explosive environment because it produces virtually no heat and cannot
cause sparks.
9. Organisms might protect themselves from predators, lure prey, and attract mates.
10. Sample answer: Compared to incandescent bulbs, LEDs produce little heat, do not require a filament, and are more
energy efficient.
11. Student answers should focus on the key drawback to CFLs: They contain mercury, a health hazard; LEDs promise
to be more environmentally friendly. LEDs, however, are still more expensive than CFLs. CFLs are considered a shortterm replacement for incandescent bulbs until LEDs become more economically practical.
DIFFERENTIATED INSTRUCTION
• Pose the following problem for mathematical/logical learners to solve. How
could you prove that ordinary light bulbs emit ultraviolet light? How could you
prove that the Sun gives off much more UV light than a light bulb? (Expose
phosphorescent material to both ordinary light bulb light and sunlight. If the
material glows, it must be receiving UV radiation. If the Sun makes it glow
brighter, it shows that the Sun emits more UV radiation). Encourage students
to share their findings with the class.
• Visual/spatial learners may have an easier time remembering each of the terms
related to light production if they draw a picture or diagram representing
each method on their flashcards. For example, the card for bioluminescence
might include a picture of a firefly.
ENGLISH LANGUAGE LEARNERS
• This section introduces a great number of terms describing methods of
light production. Students may benefit from making flashcards to review
the methods of light production. Encourage students to practise the cards
with a partner. You may wish to distribute copies of BLM 0.0-8 Term Box to
students. They can use it for recording and organizing what they have learned
about each type of light production.
• Write the word part -lumin- on the board. Explain that this word part means
“light.” Ask students to look for this word part in the vocabulary terms from
this section. Then, have students brainstorm a list of other familiar words that
contain this word part. (An example is “illuminate.”)
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