Light and Optics

1
Light and Optics

• Mirrors and Lenses

2
Explaining Light Properties

• There are two theories to explain how light
  behaves
• - The Particle model of light that says that
  light is made up of tiny particles travelling in
  a straight line
• - The Wave model of light that says that light
  travels in waves, and different colours have
  different wavelengths and frequencies.

3
Ray Model of Light

• Light radiates from the source in all directions
  as straight rays.
• These rays will keep on travelling in a straight
  line until they are bent (refracted), bounced
  (reflected), or absorbed.
• The colour of an object depends upon which
  colours are absorbed, and which are reflected.

4

• Transparent light travels right through
  objects can be clearly seen on the other side
• Eg. Regular glass windows.
• Translucent some light goes through, some gets
  reflected back, and the image is fuzzy, or
  completely distorted
• Eg. A shower door

5

• Opaque No light passes through
• The light is either absorbed or reflected.
• Causes shadows

6
Problem

• With a ray diagram, show whether your shadow is
  longer at 100pm, or 500 pm.

100
500
7
Reflection

• If an object is rough, light is reflected at all
  different angles
• The surface is unequal, so the light gets bounced
  all over the place. No image is visible.

8

• Smooth Surfaces will produce a visible image
  because all the rays reflect at the same angle.

9
Law of Reflection

• The Angle of Reflection equals the Angle of
  Incidence.

10

• The law of reflection applies even for uneven
  surfaces.

11
Refraction

• When light enters a more dense substance(medium),
  it will slow down, and bend, or refract towards
  the normal.
• When it enters a less dense substance, it will
  speed up, and bend away from the normal.

12

• This is seen when you look at a fish in the water
  the fish looks closer than it really is because
  your eyes and brain dont account for the
  refraction.

13
Mirrors

• Plane (flat) mirrors reflect exactly what is in
  front of them.
• Your eyes and brain dont account for the mirror,
  so it looks like the object is behind the mirror.
• The distance from the object to the mirror is the
  same as the apparent distance of the image to the
  mirror.

14
(No Transcript)
15
Concave Mirrors

• Mirrors that curve inward are called Concave
  mirrors.
• When light hits them, it gets reflected inwards,
  or Converges to a Focus or Focal point.

16

• Images seen in a concave mirror are upside down,
  unless you are in front of the focal point.
• This kind of mirror is used in flashlights, and
  spotlights, and in facial mirrors if you are
  close up, you will see a larger, more detailed
  image.

17
Convex Mirrors

• Curved outwards
• When light hits them, the rays diverge, or spread
  out.

Note There is still a focus, but it is
invisible.
18

• Images in convex mirrors appear to be smaller or
  farther away than they really are
• eg. Side view mirror in car
• There is also a wider field of view you can
  see more in a convex mirror than you can in a
  plane mirror.
• Used as security mirrors.

19
Concave Lenses

• Curved inwards
• Make light rays diverge
• Make images smaller and upright
• Used in some types of eyeglasses, and some
  telescopes.
• Note again, there is
• an invisible focus.

20
Convex Lenses

• Curved outward thicker in the middle.
• Causes light to converge to a focus.

21

• Again, the image will be upside down, unless you
  are looking at the image in front of the focal
  point.

22

• These lenses are used anywhere you want to
  magnify something
• Eg. Microscopes, magnifying glasses, some
  eyeglasses