Light

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Light
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I. The Eye

• Humans have two light detectors.

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• The outer layer
• 1. Cornea Clear bulge at the front of the
  eye.
• 2. Sclera Whites of the eye. For
  protection.
• B. The middle layer
• 1. Choroid Blood vessels of the eye.

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• C. The inner layer
• 1. Retina Nervous tissue. Its like the
  screen a
• film is projected on to.
• 2. Optic nerve This carries images we see
  to
• the brain.

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• D. Others
• 1. Lens Focuses light on the retina
• 2. Iris the colored part of the eye.
• 3. Pupil Black center of the iris which
• allows light to pass to the retina.

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II. Properties of Light

• A. Light travels in straight lines

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• B. Light travels VERY FAST
• 1. It travels at about 300,000 km/ sec.
• 2. It travels at 186,000 miles/second

At this speed it can go around the world 8 times
in one second. The time for light to travel to
the moon 1.3 seconds to the sun 8.3
minutes
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• C. Light travels much faster than sound.

• Thunder and lightning start at the same time, but
  we will see the lightning first.

• 2) When a starting pistol is fired we see the
  smoke first and then hear the bang.

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D. Light is an electromagnetic wave. (It
does not need a medium)
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• E. Light is made of packets of energy called
  photons that travel in waves. It has a dual
  nature in that it is both particles and waves.

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• III. We see things because they reflect light
  into our eyes

Homework
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A. Our primary source of light is the sun.
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B. A luminous object is one that produces
light such as light- bulbs, candles,
fireflies, or the sun.
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• C. illuminated objects are lit up by a light
  source. They absorb or reflect light.
• Example The moon

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D. Shadows are places where light is
blocked
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IV.When light reaches an object, A. The
light can be

• 1. Transmitted- passes through
• 2. Absorbed - travels into and stays in
• the medium
• 3. Reflected -bounces off the medium

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Reflection, absorption, transmission
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B. The object can be
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1. Transparent- All light passes through.
Examples Window glass, overhead
transparencies
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Transparent objects

• The windows on a school bus,
• A clear empty glass,
• A clear window pane,
• The lenses of some eyeglasses,
• Clear plastic wrap,
• The glass on a clock,
• A hand lens,
• Colored glass
• ALL of these are transparent. Yes, we can see
  through them because light passes through each of
  them.

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2. Translucent- some light passes
through, but not all. No clear image is
formed. Ex. Sheer curtains, a shower door.
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Translucent objects

• Thin tissue paper,
• Waxed paper,
• Tinted car windows,
• Frosted glass,
• Clouds,
• All of these materials are translucent and allow
  some light to pass but the light cannot be
  clearly seen through.

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3. Opaque- Does not allow light to pass through.
Light is blocked.Ex. a wall or door

• Opaque curtains can be used to block sunlight.

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Opaque objects

• Heavy weight paper,
• Cardboard
• Aluminum foil,
• Mirror, bricks, buildings,
• Your eyelids and hands,
• Solid wood door,
• All of these objects are opaque because light
  cannot pass through them at all.
• They cast a dark shadow.

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V. Methods of producing (making) light

• A. Incandescent Light - This means
• glowing hot. Light that comes from
• thermal radiation.
• Examples Light bulbs, glowing
• coals

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Incandescent Glowing Hot
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• B. Chemical reaction- Burning something or
• chemicals reacting to produce light.
• Examples candles, glowsticks

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• C. Electric current through a gas
• Examples neon lights

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• D. Fluorescent- Light produced by using electrons
  to bombard molecules of a gas in a tube. (It is
  cooler than incandescent and cheaper.) Ex
  Fluorescent bulbs

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VI. Color

• A. White light is made up of all the
• colors. They appear in a spectrum.
• It can be abbreviated as ROYGBIV

We can demonstrate this by splitting white light
with a prism This is how rainbows are formed
sunlight is split up by raindrops.
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The colors of the rainbow

• Red
• Orange
• Yellow
• Green
• Blue
• Indigo
• Violet

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• B. The color an object appears depends on the
  colors of light it reflects.

For example, a red book only reflects red light
White light
Only red light is reflected
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A pair of purple trousers would reflect purple
light (and red and blue, as purple is made up
of red and blue)
Purple light
A white hat would reflect all seven colours
White light
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Using colored light

• If we look at a colored object in colored light
  we see something different. For example,
  consider a football kit

Shirt looks red
White light
Shorts look blue
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• In different colors of light this kit would look
  different

Red light
Shirt looks red
Shorts look black
Shirt looks black
Blue light
Shorts look blue
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Red socks reflect red and absorb all other
colors.
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C. The primary colors of light are red,
blue, and green.
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Adding colors

• White light can be split up to make separate
  colors. These colors can be added together
  again.
• The primary colors of light are red, blue and
  green

Adding blue and red makes magenta (purple)
Adding blue and green makes cyan (light blue)
Adding all three makes white again
Adding red and green makes yellow
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• E. The primary colors
• of pigments are.. yellow, cyan, and
• 
  magenta
• When mixed together,
• they produce Black

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VII. Reflection

• A. Reflection - The bouncing back of light

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• 1. Regular reflection - Rays hit and are
  reflected at
• the same angle. A clear image is formed.

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• 2. Diffuse reflection- Reflected light is
• scattered due to an irregular (bumpy)
• surface. No image is formed.

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Clear vs. Diffuse Reflection

• Smooth, shiny surfaces have a clear reflection

Rough, dull surfaces have a diffuse
reflection. Diffuse reflection is when light is
scattered in different directions
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B. The angle of incidence equals the angle
of reflection.
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• The Law of Reflection

Angle of incidence Angle of reflection
In other words, light gets reflected from a
surface at ____ _____ angle it hits it.
The same !!!
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Using mirrors

• Two examples

2) A car headlight
1) A periscope
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C. Mirrors and shiny surfaces reflect light.

• 1. Types of mirrors
• A. Plane mirror mirror with a perfectly
  flat
• surface.
• B. Concave mirror- mirror where the surface
• curves inward.
• C. Convex mirror- mirror where the surface
  curves
• outward.

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VIII. Refraction

• A. Refraction- the bending of light as it
  
• passes from one medium (material) into
• another due to a change in speed.

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B. Refraction occurs in prisms and causes
rainbows.
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Red is always on the top of a rainbow
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Refraction makes the ruler look like it is bent.
(It is not.)
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Refraction Light slows down as it enters the
glass and speeds back up in the air.
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Refraction makes fish appear in a different
location
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• D. Mirage- An optical illusion caused by the
• refraction of light by the atmosphere.
  
• Examples Seeing water that isnt there, oil
  drops giving rainbows, mirage boxes.

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• IX. Diffraction
• A. Diffraction is the bending of waves
• around the edge of an obstacle or
• through a groove.

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X. Lenses

• Lens - Any transparent material that causes
  light to converge or diverge
• B. Convex Lens- A lens that converges, or
• brings together light rays. It is thicker in
  the
• center.

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C. Concave lense- A lens that diverges, or
spreads out light rays. It is thinner in the
center.

• Convex lens
• Concave lens

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XI. Polarized light-

• A. Polarized light- Light that vibrates in
  only one plane.
• B. Polarizing filters allow light in only one
• direction through.
• Ex. Sunglasses, cameras Polarizing filters allow
  
• light through in only one direction

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XII. Lasers

• A. Laser- A device that produces an
  intense
• beam of light of one color
• B. Coherent light Light that is all
  one wave
• length and in step
• C. Laser stands for Light Amplification
  by
• Stimulated Emission of Radiation.

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D. Uses of lasers

• 1. measurement
• 2. medicine
• 3. industry (UPC codes, CDs)
• 4. Fiber optics
• 5. Holograms
• 6. Laser levels
• 7. Light shows
• 8. Laser pointers
• 9. CDs (To write and to read the CD)

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XIII. Optical instruments

• A. Cameras
• B. Microscopes
• C. Telescopes
• D. Lasers

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Notes Ch. 25 and 26

• Light
• A. Definition Packets of energy
• (photons)
  traveling in
• waves.
• C. Speed of light in
• Air 300,000 km/ sec
• Water 223,000 km/sec
• Glass 200,000 km/ sec
• Diamond 124,000 km/sec

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• F. The primary colors of
• light are Red, blue, and green
  
• When mixed together,
• they produce White

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• red light green light yellow
• blue light red light magenta
• blue light green light cyan

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• B. Location at which parallel Focal point
• light rays reflected from
• a mirror or passed through
• a lens meet and form an
• image.
• C. The angle of incidence is
• equal to the angle of reflection

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Refraction