Junior High

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Junior High

• Light and our World

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Section 1 Mirrors and Lenses

• Rays are arrows used to the path of a single
  light wave.
• Ray Diagrams are used to show where images are
  formed by mirrors and lenses.
• There are three kinds of mirrors plane, convex,
  and concave.
• Plane and convex mirrors produce virtual images.
• Concave mirrors produce both virtual and real
  images.

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• A virtual image is an image through which light
  can not travel.
• A real image is formed in front of the mirror and
  light does travel through the image. This image
  occurs when you are further away from the mirror
  than the focal point of the light reflected by
  the mirror. When you are closer to the mirror
  than the focal point you will see a virtual image
  in the back of the mirror. It is right side up
  and light does not pass through it.

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• Lens a transparent object that refracts light
  waves.
• Convex Lenses Thicker in the middle. Form
  virtual images larger than the object if the
  object is less than one focal length away. Form
  a smaller real image if the object is more than
  two focal points away from the lens.
• Concave Lenses Thinner in the middle. Rays
  entering the lens are spread out and never meet
  therefore they never form a real image. They
  form virtual images.

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Section 2 Light and Sight
The main parts of the eye appear below. The
image was taken from Holt Science and Technology
PowerPoint notes prepared by the company for this
unit.
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The path of light in your eye

• 1. Light enters the cornea (outer protective
  membrane) and is refracted toward the pupil.
• 2. Light passes through the pupil (the opening
  in the eye). The outer colored part of your eye
  is the iris. It contracts to let less light in
  or relaxes to let more light in.
• 3. Light passes through the lens ( a convex
  transparent lens that refracts light to a focal
  point in the back of the eye).
• 4. Light passes to the retina (the back surface
  of the eye that contains the photoreceptors rods
  and cones) This is where light is detected and a
  message is generated to the nervous system..
• 5. The optic nerve takes the information from
  the eye to the brain for translation

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Vision Problems

• There are three common vision problems
• Near sightedness The eye is too long and the
  light from the lens is focused in front of the
  retina. Objects far away appear blurry. A
  concave lens causes the light to refract outward
  and the lens in the eye can focus on the retina.
• Far sightedness The eye is too short and the
  light from the lens focuses behind the retina.
  Objects close appear blurry. A convex lens
  placed in front of the eye refracts the light
  through the lens of the eye so it focuses on the
  retina.
• Color Blindness This is a genetic disorder that
  is linked to the X chromosome therefore it
  appears far more in males. There are three
  different kinds of cones and they each detect
  different wavelengths of light. They are red,
  blue and green cones.

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Eye Surgery

• Eye surgery is used to correct the shape of the
  cornea and adjust the amount of light it refracts.

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Section 3 Light and Technology

• Optical instruments any device that uses lenses
  and or mirrors to help people make observations.
• Cameras use lenses to focus light on the film.
  The shutter of the camera opens and closes to
  allow a certain amount of light to expose the
  film.
• Telescopes There are three different types of
  telescopes. Only two use lenses and mirrors.
  The third uses radio waves.
• Refracting telescope Uses lenses to refract
  light through a tube. The light enters the
  objective lens, passes through the tube, exits
  the eyepiece lens to your eye. The bending of
  light distorts images.
• Reflecting Telescope Uses mirrors to reflect
  light to a convex eyepiece lens. Generally
  produces clearer images.

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• Microscopes The light microscopes use convex
  lenses to magnify tiny objects.
• Lasers Laser light is light of one wavelength
  tightly focused. The Laser light is produced by
  exciting helium and neon gases. The neon atoms
  release photons of red light that are
  concentrated and sent out a small opening in a
  concentrated beam. Plane mirrors reflect and
  concentrate the beam before it exits.
• Uses of lasers
• 1. Make hologram images (three dimensional
  images)
• 2. Cutting materials
• 3. In surgery
• 4. CD players

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• Optical Fibers Thin glass wire that act like
  pipes that carry light. They have TOTAL INTERNAL
  REFLECTION. This means that light is completely
  reflected and not lost.
• Polarized Light Light waves that vibrate in
  only one plane. Polarized sunglasses reduce
  glare. Glares are light waves that are polarized
  horizontally. Polarized sunglasses cut out these
  waves.
• Communication technology
• 1. Cordless telephones The base signal is
  translated to a radio wave and transmitted to the
  phone.
• 2. Cellular phones They use microwaves to
  transmit information
• 3. Satellite Television Companies broadcast
  information in the form of microwaves from
  satellites orbiting the Earth.
• 4. Global Positioning System (GPS) 27
  satellites orbiting Earth continuously send
  microwaves that can be picked up receivers on
  Earth.