Light

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Light Part 2Seeing

• Year 7 Science

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Front View of the Eye
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Parts of the eye for protecting eyeball

• Eyelids are skin flaps on the outside of your
  eyes. They are used to protect the eyeball from
  dust, smoke, bright light or physical injury.
• Tear Glands are used to provide liquid that helps
  lubricate the eye. The lubricant is also
  important for washing away small particles of
  dust that may irritate the eye.
• The small hole in the inside corner of the eye is
  the opening of the tear duct. The tear ducts
  drain any excess liquid produced by the tear
  glands.

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Front View of the Eye
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Cross section view of eye
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Parts of the eye used in vision

• The Cornea is a clear thin skin that covers the
  front of the eye and allows light to pass into
  the eyeball. The cornea is curved so that light
  is bent or refracted towards the pupil.

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Refraction

• The bending of light is called Refraction. It
  happens when light travels between substances of
  different densities like air to water. Try this
  experiment at home to see how refraction
  happens..

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Parts of the eye used in vision

• The coloured part in front of the eye is called
  the iris. This is a ring of muscle which changes
  in size, depending on the light intensity just
  like the aperture in a camera lens.
• When we say someone has brown or blue eyes we are
  referring to the colour of the iris.

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Parts of the eye used in vision

• The dark central area is the pupil and is
  actually an opening in the iris through which
  light passes. It is large when there is little
  light and small when there is plenty of light.

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Parts of the eye used in vision

• As light rays continue to pass through the eye,
  they are refracted a little more by the lens in
  the eye.
• The lens is clear and jelly-like and is connected
  to muscles which can make it thick or thin.
• The lens bends light to focus it on the retina at
  the back of the eyeball. The retina is sensitive
  to both the colour of light and brightness of
  light.

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What do lenses do ?

• The lens in your eye bends light in order to
  focus it on the retina. The drawing below shows
  how light rays are bent with a lens
• Notice how the lens bends light rays so they come
  to a point. We call this point the focal point or
  focus.

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Types of lenses

• Lenses can be either converging or diverging.
  Your eye uses a converging lens.

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How the eye focuses
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Sending image signals to the brain

• Although your eye receives the light and produces
  an image of what you see, it is your brain that
  interprets and makes sense of the image.
• The receptors on the retina respond by sending
  signals to the optic nerve which in turn sends
  signals to the brain.

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Summary
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(No Transcript)
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Homework

• Read pages 188-189 of Core Science 1 text and
  answer all Remember and Think Activities on page
  189.

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Short-sightedness
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Long-sightedness