Optical Systems make use of Mirrors and Lenses

light is represented as a straight line or ray
that shows the direction the light wave is
travelling. Remember that light is made up of
waves and can be described using
wavelength and frequency.
Transparent – a material that allows light to
pass through freely. All or most of the light is
transmitted.
Translucent – a material, such as frosted glass,
that lets most light rays through, but scatters
them. Some light is transmitted.
Opaque – a material that prevents any light
from passing through. All or most of the light is
absorbed or reflected.

Transparent?

Translucent

Opaque




You can use the ray model to predict where
shadows will form and how large they will be.
The closer the object is to the light source the
larger the shadow.
The further the object is from the light source
the smaller its shadow will be.
No shadow can be perfect*









If a wave strikes the sea wall on an angle how will it bounce
off?
** precisely the same angle
Incident ray= incoming ray
Reflected ray= ray that bounces off barrier
Normal= “dotted line” perpendicular to the boundary
between two materials. Drawn at right angles to the solid
barrier
Angle of incidence= formed by incident beam and normal
Angle of reflection= formed by the reflected beam and
normal
Why is it called the Law of Reflection?
** angle of reflection = angle of incidence
Normal line
When light moves into a medium of higher
density it slows down (i.e. air to water, or air to
glass) and moves towards the normal line.
When light moves into a medium of lower
density it speeds up (i.e. water to air or glass to
air) and bends away from normal.
Bowl of Water

Place a coin at the bottom of a bowl/cup.
Step back until the coin just stops being visible over the lip of the bowl/cup. Then have someone slowly pour
water into the bowl.
What do you see? Why does this happen?



Insert a pencil at an angle into the cup.
Try looking at the pencil at different angles (above and below the water line).
What do you see? Does anything change, or stay the same? Why?


Pencil
Vegetable Oil and a Cup












Put the shot glass inside the larger glass.
Fill the larger glass with water. Just enough to cover the smaller glass by an inch
Look at the glass from different angles.
Do you see the drinking glass? Why?
Spill out the water and dry the shot and larger glass.
Put the shot glass back inside the larger glass
Fill the larger glass with cooking oil.
Look at the glass from different angles.
Do you see the drinking glass? Why?
Pour the vegetable oil back into the plastic cup. Dry and clean both glasses for the next group .
Bowl of Water

When the bowl is empty the edge of the bowl stops you seeing the coin. When the bowl is full of
water the light bends over the edge so you can see the coin.

Have you ever noticed that things at the bottom of a pool or river always look closer to the surface
than they really are? This is because of the way light is bent through water and is an effect of
refracted light.
Pencil

From above, the pencil seems to bend at the water line because refraction has occurred between the
two mediums of water-air. The pencil also looks bigger underwater. This is because of the glass has
curved surfaces and therefore the water in it acts as a convex lens.
Vegetable Oil and a Cup

As light passes through one medium to another (water-air, glass-air), the light is bent (refracted) at
the boundary between the two mediums. This happens because light travels at different speeds
through different mediums. Light moves through petroleum products (including cooking oil) at about
the same speed as it does through the glass. Therefore, as light passes between glass and oil it
doesn’t bend at the boundaries, leaving the boundaries invisible.
Refraction of light can also occur
when light travels through air at
different temperatures. Warm air
is less dense than cooler air. When
light enters cooler air it will slow
down and bend towards normal.
Mirage of water on pavement on a hot summer
day. How does this happen?
Answer: Air close to the pavement
becomes superheated. As light travels
from the road to your eye, it slows
down when it hits the cooler air above
the highway. It will slow down and
bends towards normal. The effect
causes a water mirage.
http://hubblesite.org/gallery/spacecraft/22/
http://solarcooking.org/
http://www.physicsclassroom.com/Class/refln/u
13l3d.cfm

More or less than meets the eye.
A real image is one in which light rays actually come from
the image.
 In a virtual image, they appear to come from the reflected
image - but do not. In a flat mirror, for example, the virtual
image of an object is behind, or "inside" the mirror, but
light rays do not originate from there. Real images form
outside the system, where emerging light rays cross and
are "caught"...inside camera...on a screen...or in a
“Mirage.”


All concave mirrors can produce real images under certain
circumstances.

Plane Mirrors
All mirrors reflect light according to the law
of reflection. Plane mirrors form an image
that is upright and appears to be as far behind
the mirror as the object in front of it is.

Plane mirrors produce an image with the same
orientation as well. Take a look at this video ...

http://www.youtube.com/watch?v=H_DtsxVGG0

Concave mirrors curve inward. They can form an
image that is inverted or right side up, and can be
larger or smaller than the object.

Parallel light rays bounce off the curved surface and
meet at a single point called the focal point. We
describe the lights rays joining together as
converging.

Object’s distance to focal point of mirror: far= small
and upside down image. Close= remains inverted, but
larger. If the object is between the focal point and the
mirror=object is larger and upright.




Spotlights
Flashlights
Lighthouses
Car headlights
(bright light is placed at focal point)

Convex mirrors bend outwards. Remember the
question about why “objects in mirror are closer than
they appear?”
1.
2.
3.
4.
The image is smaller than the object.
The image distance is smaller than the object distance.
The image is upright.
More can be seen in convex mirror opposed to a plane
mirror.

They reflect parallel light rays as if they came from the
focal point behind the mirror. The light rays do not meet.
Instead, they diverge (spread a part after reflecting).

Which mirror is best suited for security
purposes in retail stores and why? (Plane,
concave or convex?)

Materials: Ray box, concave/convex lenses, and a printed page

1) Shine the ray box at a concave lens. Observe how the rays are
affected. Draw your observations
2) Look through the concave lens at some printed text. Observe the
appearance of the print. Draw your observations






3) Shine the ray box at the convex lens. Observe how the rays are
affected. Draw your observations.
4) Look through the convex lens at some printed text. Observe the
appearance of the print. Draw your observations.
Compare what you observed about the appearance of the text with each
of the two lenses.
Which type of lens would be best used as a magnifying glass?
What might the other kind of lens be used for?

Concave lenses are thinner in the middle
than at the edge. Light rays that pass through
a concave lens diverge
The rays never
meet at focal
point and always
bend outwards.

Concave lenses work to make something
look smaller, so they're not quite as common
as convex (magnifying) lenses.

Telescopes
Binoculars
Eyeglasses







Convex lenses are thicker in the middle of
the lens and they thin out towards the edges.
When light rays pass through they converge
and meet at a focal point.
When light rays passes through the center it
continues in a linear path.
When light rays passes through the more
curved sides, they refract, i.e. Bend
Images seen through convex lenses are larger
than concave images.

Eyeglasses

Magnifying glass


Convex lenses and concave mirrors both
reflect light rays that converge at the focal
point
Like concave mirrors, convex lenses also
produce reflective images that are either
smaller/ larger, or upright/inverted to the
object itself. The object’s position to the focal
length and lens will determine the image
produced.

Explain why a drop of water placed on the
page of a book magnifies printing beneath it.