Where do we get light?

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Where do we get light?
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Luminous and Illuminated Objects
A luminous object is one that produces light. An
illuminated object is one that reflects light.
Illuminated Objects
Luminous Objects
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• We see things because they reflect light into our
  eyes

Homework
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How does light behave?
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Reflection of Light

• Reflection occurs when a wave bounces back after
  striking a barrier.
• Example a reflection in a mirror.

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Three things that affect how light is reflected

• Surface of the Object
• Color of the Object
• Shape of the Object

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Clear vs. Diffuse Reflection
Surface of the Object

• 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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Color of the Object

• Ever notice that an asphalt driveway seems hotter
  on a summer day than a concrete sidewalk?

This occurs because light that is not reflected
from the surface of an object may be absorbed by
the object and converted into thermal energy.
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Shape of the Object

• Reflection from a mirror

Normal
Reflected ray
Incident ray
Angle of reflection
Angle of incidence
Mirror
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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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Types of Mirrors

• Plane (flat), Concave, Convex

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Plane Mirrors

• Flat Surface
• Light is reflected straight back, resulting in an
  upright image that is the same size as the
  original object.

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Concave Mirrors

• Curves Inward (like the inside of a bowl)
• If an object is very close to the mirror, light
  is reflected in a way that an enlarged, upright
  image is produced.
• If the object is very far away, the image is
  reduced in size and upside down.

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Convex Mirrors

• Curves Outward
• Results in an image your eyes detect as upright
  and reduced in size.
• The side mirrors on cars are convex mirrors.
  (Objects in mirror are closer than they appear.)

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Refraction of Light

• Refraction is the bending of a wave as it passes
  from one medium to another.

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What causes the light to bend?

• Whats different about air and water?
• DENSITY the amount of mass in a certain volume
  of a substance (mass/volume)

WATER
AIR
gas
liquid
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Example of Refraction
When a straw is placed in water it looks like
this In this case the light rays are slowed down
by the water and are bent, causing the straw to
look broken. The two mediums in this example are
air and water.
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Another Example

• When you use a magnifying glass, the object
  appears larger because of refraction.
• The light waves traveling in the air change
  direction when they enter the glass of the lens,
  and then again when they move from the glass back
  into the air again.

Lens
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Diffraction of Light

• Diffraction is the bending, spreading, and
  interference of waves when they go through a
  narrow opening.

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Diffraction Patterns

• Radio waves can diffract around hills, mountains
  or even the whole planet.
• Light waves can diffract through tiny slits.
• X-rays can diffract around atoms.

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Electromagnetic waves have a huge range of
wavelengths.

• If the wavelength is of a similar size to a gap
  in a harbor wall, then the wave will diffract as
  shown below.

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• If the wavelength does not match the size of the
  gap, then only a little diffraction will occur at
  the edge of the wave.

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Transmission of Light

• Transmission is the passing of waves through a
  medium.

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Think about a radio station

• An electromagnetic wave is produced.
• The wave travels from the stations transmitter
  out in all directions at the speed of light.
• Even though you cannot hear radio waves when your
  radios turned off, the waves are still being
  transmitted in the room.

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What happens when light hits these objects?

• Glass of water
• School bus window
• Notebook paper
• Waxed paper
• Plastic wrap
• Tissue paper
• Cardboard
• Textbook
• Hand lens

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Many materials are classified by how well they
transmit light.

• Three Types of Materials
• Transparent
• Translucent
• Opaque

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Transparent

• A material that permits light to pass through

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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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Translucent

• A material that transmits some light but also
  scatter light in all directions

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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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Opaque

• A material that allows no light to pass through

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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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• Shadows

Shadows are places where light is blocked