Chapter 18: Light and Optics

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Chapter 18 Light and Optics
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Objectives

• Summarize the science of optics.
• Describe how mirrors and lenses can be combined
  to make complex optical tools.
• Explain how optical tools are used to extend
  natural vision.
• Recognize how laser light is made and used in
  optical technology

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Optics is the science of light and vision

• Optics is the study of visible light and the ways
  in which visible light interacts with the eye to
  produce vision.
• Mirrors, lenses, eyeglasses, cameras, lasers are
  all optical tools.

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Fiber Optics

• Used to transmit information efficiently.
• EX) Fiber Optic Cables.

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Fiber Optics

• Is Technology based on the use of light to send
  signals through transparent wires called optical
  fibers
• Very important in communications for telephones,
  TV wires, and broadband internet connections.
• Medical uses to see inside a patients body

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Lasers

• A laser is a device that produces an intense,
  concentrated beam of light that is brighter than
  sunlight.
• A laser is made in a special tube called an
  optical cavity in which an energy source
  stimulates material to give off light waves.

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Laser Beams

• A Laser Beam can travel great distances without
  spreading because its light waves are parallel
  and very concentrated.
• The light waves in a laser beam are all one
  wavelength and in one phase.

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Uses of Lasers

• Surveyors use them to measure distances and
  angles.
• Used to read bar codes, to scan images and pages
  of text and to create holograms

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Future Uses of Lasers

• Scientist plan to use them in nanotechnologyperfo
  rm extremely fine operations.
• New ways of transferring energy.
• Supply energy for the spacecraft.

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Mirrors and Lenses can be more Powerful Optical
Tools

• For example Mirrors and lenses can be combined
  with each other, as they are in an overhead
  projector.

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Microscopes

• Used to see small objects.
• A Microscope enlarges images using a combination
  of convex lens. (2)
• Most microscopes use a light or mirror to shine
  more light on the object.
• Page 613

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Telescopes

• A reflection telescope has a CONCAVE mirror that
  gathers and focuses light.

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Telescopes

• Used to see objects to far away to see well with
  the naked eye.
• 2 Types
• Refracting telescope is made by combining lenses.
• Reflection is made by combining lenses and
  mirrors.

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Refraction Reflection
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Lights, Camera, Action.

• Most film cameras focus images
• Like the eyes
• Read Page 614

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• Objectives
• Describe how mirrors control reflection.
• Describe how mirrors produce images.
• Identify how a material medium can refract light.
• Describe how lenses control refraction.
• Recognize how lenses produce images.

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Mirrors use Regular Reflection

• When light waves strike an object, they either
  pass through it or they bounce off its surface.
• The law of reflection states that the angle of
  reflection equals the angle of incidence.

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Regular Reflection

• The reflection of parallel light rays all in the
  same direction is called regular reflection.
• Surface of the object is smooth, like a mirror,
  light rays that come from the same direction will
  bounce off in the same new direction.

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Diffuse Reflection

• If the surface is not very smooth, light rays
  strike it from the same direction and bounce off
  in many new directions.
• The reflection of parallel light rays in many
  different directions is called diffuse
  reflection.
• EX) Paper, Cloth

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An Image

• When you look in the mirror, you see an image of
  yourself.
• An image is a picture of an object formed by
  waves of light.
• The image of yourself is reflected off of you,
  onto the mirror.

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Law of Reflection

• States that the angle of incidence equals the
  angle of reflection
• EX) A ray of light hits a mirror at an angle of
  incidence, the reflection angle is equal.

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Focal Length

• The focal length of a lens is the distance from
  the center of a lens to its focal point.

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Flat Mirrors

• Looks Exactly like you
• Produces an image that is identical, but opposite
  to how you look

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Convex

• A Convex mirror or lens is curved outward.
• A convex lens brings light rays to a focal point.
  
• The distance from the center of the lens to the
  focal point is the focal length.
• A convex lens forms a right-side up image when
  the object is less than one focal length away.
• If the object is twice the distance, the image
  will appear Upside down smaller
• A convex mirror will produce an image that is
  right side up smaller.

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Concave

• A Concave mirror or lens is curved inward towards
  the center.
• Parallel light rays that pass through a concave
  mirror are reflected to a focal point

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Concave/Convex
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Focal Point

• The rays striking a concave mirror cross and then
  move apart again. The point at which the rays
  meet is called the focal point of the mirror.
• P. 597

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Light Waves and Refraction
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Light Waves

• Light Waves move at different speeds through
  different Mediums.
• A ray of light will slow down when it moves from
  air into the denser medium of a pond.
• The amount direction a light ray bends when it
  enters a new medium depend on how dense the
  medium is.
• A light wave enters a new medium at an angle
  other than 90º, the wave will turn toward the
  normal.

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Electromagnetic Waves

• Electromagnetic Waves from a star will travel
  through empty space, they travel in straight
  lines because the medium has not changed.

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A medium can refract light

• Some light rays reflect off the surface of glass.
• Refraction occurs when a wave strikes a new
  mediumsuch as the windowat an angle other than
  90 and keeps going forward in a slightly
  different direction.

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Refraction of Light

• Page 600
• Waves moving at an angle into a denser medium
  turns toward the normal.
• Waves moving at an angle into a thinner medium
  turn away from the normal

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Refraction and Rainbows

• Rainbows are caused by
• Refraction and reflection of
• Light through spherical water
• Drops, which acts as prisms.
• Only one color reaches
• Your eye from each drop.
• Red appears at the top of a
• Rainbow because it is coming
• From higher drops, while violet
• Comes from lower drops.

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Shape determines how lenses from images

• Just as a curved mirrors distort images, certain
  transparent mediums called lenses alter what you
  see through them.
• A lens is a clear optical tool that refracts
  light. Different lenses refract light in
  different ways and form images useful for a
  variety of purposes.

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Convex Concave Lenses

• A convex lens causes parallel light rays to meet
  at a focal point
• A concave lens causes parallel light rays to
  spread out.
• Page 601 602

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Images Formed by Lenses

• Notice the distance between the penguin and the
  lens in the illustration on page 602.
• The distance is measured in terms of a focal
  length, which is the distance from the center of
  the lens to the lenss focal point.

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To summarize

• If you look at an object through a concave lens,
  youll see an image of the object that is right
  side up and smaller than the object normally
  appears.
• If you look at an object through a convex lens,
  the image could be formed upside down and larger
  if two focal lengths away. Or it will appear
  right side up and larger if one focal length away.

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How does a camera lens form an image

• A camera lens uses refraction to focus light on
  the film, or in a digital camera.
• When a ray of light passes from a less dense to a
  more dense medium (such as from air to glass) it
  slows down. If it strikes the glass surface at an
  angle, it is also bent a little, and this is
  called refraction. When it passes back into air,
  it speeds up again, and is again refracted if the
  surface is at an angle.

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18.3The Eye is a Natural Optical Tool

• Objectives
• Recognize how the eye depends on natural lenses.
• Explain how artificial lenses can be used to
  correct vision problems.

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Eyes gathers and focuses light

• Eyes transmit light, refract light, and respond
  to different wavelengths of light.
• Eyes contain natural lenses that focus images of
  objects and then sends signals to the brains.
• The brain interprets these signals as shape,
  brightness, and color.

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How Light Travels through the Human Eye

• Light enters the eye through the cornea, a
  transparent membrane that covers the eye.
• The two parts of the eye that refract light are
  the CORNEA AND LENS

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Retina

• The retina detects an image and send signals to
  the brain
• The CORNEA acts like a convex lens
• The lens adjusts to focus an image on the retina

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How Light Travels through the Human Eye

• Light continues through the pupil, a circular
  opening that controls how much light enters the
  eye.
• The pupil is surrounded by the iris, which opens
  and closes to change the size of the pupil.

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How Light Travels through the Human Eye

• Next, the light passes through the lens. It
  refracts light to make fine adjustments for near
  or far objects.
• The lens is connected to tiny muscles that
  contract and relax to control the amount of
  refraction that occurs and to move the focal
  point.

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How Light Travels through the Human Eye

• 4. The light then passes through he clear center
  of the eye and strikes the retina. The retina
  contains specialized cells that respond to light.
  Some of these cells sends signals through the
  optic nerve to the brain.

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How the Eye Forms Images

• For a complete image to be formed in the eye and
  communicated to the brain. The Retina plays a
  very important role.

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Retina Rod Cells

• Rod cells distinguish between white and black and
  shades of gray. Help in night vision.

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Retina Cone Cells

• Cone cells- respond to different wavelength of
  light so they detect color. There are three
  types Red, Blue, and Green. They respond to
  other colors by using a combination of the three.

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Cameras

• Just like our eyes have to focus on an image, we
  must move the lens of a camera to focus an image
  onto film

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Corrective Lenses can Improve Vision

• How many of you wear contacts or glasses?
• About 36 million wear contact lenses
• When the image formed by the lens of the eye does
  not fall exactly on the retina. A blurry image
  is formed. Artifical lenses are used to correct
  this problem.

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Farsighted

• Objects are clearer to a farsighted person when
  the objects are farther away. It occurs when the
  lens of the eye focuses an objects image behind
  the retina.This can be caused by aging.
• A person who is farsighted can be helped by a
  convex lens, that make light rays converge
  farther towards the retina.

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Corrective Lenses

• Nearsighted cannot see objects clearly unless
  they are near. It occurs when the lens of the
  eye focuses the image in front of the retina.
• A person who is nearsighted wears glasses to
  spread light out so that the image is focused on
  the retina.

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Surgery

• Doctors can use surgical procedures to shape the
  cornea.
• To correct nearsightedness, surgeons remove
  tissue from the center of the cornea.
• To correct farsightedness, surgeons remove tissue
  from around the edge of the cornea.
• http//www.youtube.com/watch?vdZZguJNitnU

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Contacts

• Contact lenses also correct vision by changing
  the way the cornea refracts light.
• CONTACTS work with the cornea and tears to act as
  a single lens.
• This is only a temporary fix.

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Objectives

• Identify sources of EM waves
• Recognize how EM waves transfer energy
• Describe how different EM waves are used
• Observe how to detect visible light
• Explain how visible light is produced
• Describe bioluminescence
• Identify types of artificial light
• Recognize how light waves interact with materials
• Recognize why objects have color how colors are
  produced

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Visible Light Spectrum
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Electromagnetic Waves

• Electromagnetic waves can be converted into
  useful forms (Microwave ovens)

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Incandescence Bioluminescence

• Incandescence is the production of light by
  materials at high temperatures.
• Some organisms can produce their own light, this
  is called bioluminescence.

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Artificial Lighting

• There are many types of artificial lighting
  (Textbook Page 571-572)

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Light Waves

• Light can be transmitted, reflected, absorbed or
  scattered.
• A prism is a tool that uses refraction to spread
  out different wave lengths of light

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Polarization

• Polarization is a quality of light in which all
  of its waves vibrate in the same direction