Science 8: Unit C

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Science 8 Unit C Light and Optical Systems

• Topic 1 What is Light?

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I. Light is a form of Radiant Energy

• Light is a form of energy that we can see.
• Light travels in waves. Light, in fact is a kind
  of radiation. This means that light rays can
  travel across empty space. Other kinds of waves
  like sound waves need some kind of material to
  travel through. Thats why an astronaut cannot
  hear the explosion of his spaceship, but can see
  it explode.
• Light travels in straight lines. We call these
  straight lines rays. The more rays there are in
  an area, the brighter the light will look.

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I. Light is a form of Radiant Energy Contd

• Since light is a form of energy, different light
  sources have more or less energy than others. We
  measure light energy by its intensity. The
  brighter the light, the more energy it has.
• Light rays can be reflected, diffracted,
  refracted, or absorbed by an object. Black
  objects tend to absorb most light that hits them
  and white objects tend to reflect most light rays
  that hit them.

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II. Light Sources

• Light can either come from natural (eg. sun,
  stars, animals) or artificial sources (eg. light
  bulbs, TV screens). Here are a few types of
  artificial light sources.

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1. Incandescent Light

• Traditional light bulbs which use a thin metal
  wire to conduct electricity. The electrical
  current causes the wire to glow white hot
  producing light. An advantage of these bulbs is
  that theyre cheap, a disadvantage is that they
  are very inefficient losing 90 of its energy to
  heat.

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2. Fluorescent Light

• Fluorescent Light bulbs. An electrical current is
  run into a tube full of mercury vapor. The
  mercury atoms become excited and produce UV
  radiation. The UV radiation reaches phosphor
  powder on the tube which also gets
  energized/excited and releases light energy that
  we see. An advantage of fluorescent lights is
  that they are much more efficient than
  incandescent lights. A disadvantage is that they
  contain poisonous mercury vapor.

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3. Phosphorescent Light Sources

• Glow in the dark toys/stickers/tools. Similar to
  fluorescence except that light energy is stored
  over time and then released in the dark after the
  light source has been removed. This process of
  gradual release of light is called
  phosphorescence.

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4. Chemiluminscent Sources

• Glow Sticks. Chemical reactions produce energy in
  the form of light. So stored chemical energy
  produces light energy. In a glow stick a barrier
  separates the two reactants. When the barrier is
  broken the reactants mix producing the light
  energy.

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5. Bioluminescent Sources

• Deep Sea Creatures. Biochemical reactions in
  certain living things produce light energy. This
  is especially helpful in areas where there is no
  light from the sun such as the ocean floor.

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III. The Cost of Lighting

• Light energy in Alberta is provided by your local
  power company (Epcor, Enmax) and is part of your
  power bill. The formula to find out how much the
  light will cost is
• Cost (in or ) Power of bulb (in kW) Time
  being used (in h) Price of Power (in or )

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IV. Transparent, Translucent, and Opaque Objects

• Transparent objects allow light rays to pass
  through without getting bent. You see a clear
  image across a transparent object.
• Translucent objects allow only some light rays to
  pass through and most of these are bent. You can
  see light, but you cant see a clear image.
• Opaque objects absorb or reflect all light rays
  allowing none of them to pass through. You see no
  light or images.