Unit 33 - Optics
Optics is the study of the behavior and properties of light.
This includes it’s interactions with objects including mirrors,
lenses, and substances which reflect or scatter light.
When Light Strikes an Object
When light strikes an object, the light
can be reflected, transmitted,
scattered, or absorbed.
Magnification or Reduction
Mirrors
Mirrors reflect light at the
same angle it receives it.
But, if the mirror is curved…
Plane mirror
Mirrors
Have you ever gone to the fun house
and looked at yourself in the many
different mirrors there?
Have you ever wondered how the
image forms?
The image formed is a result of
reflection, which you learned about in
the previous unit.
Plane mirror
•There are three types of mirrors: plane,
concave, and convex.
•A plane mirror is a flat mirror
Plane Mirror
•The law of reflection states that the angel of
reflection is equal to the angle of incidence.
•Incident ray = the incoming ray that approaches
the mirror
•Angle of incidence = the angle the incident ray
makes wit a line drawn perpendicular to the
surface of the mirror.
•Reflected ray = the ray the mirror reflects from
the incident ray.
•Angle of reflection = the angel the reflected ray
makes with the perpendicular line.
Plane mirror
- Reflection and Mirrors
Concave Mirrors
A mirror with a surface that curves inward like the inside of a
bowl is a concave mirror.
Parabolic Mirrors
They can reflect the light to a focal point,
making it the strongest signal possible.
Satellite dishes direct the radiowaves to the
antenna which sits at the focal point
Parabolic mirrors direct sunlight to a focus to
absorb energy and generate electricity.
The Focal Point
Concave Mirrors
Ray diagrams show where an image forms and the size of the
image. The steps below show how to draw a ray diagram.
Concave Mirrors
Concave mirrors can form either “virtual images” or “real images”
Convex Mirrors
A mirror with a surface that curves outward is called a
convex mirror.
Comparing and Contrasting
As you read, compare and contrast concave and convex
mirrors in a Venn diagram like the one below. Write the
similarities in the space where the circles overlap and the
differences on the left and right sides.
Concave Mirror
Convex Mirror
Real images
Enlarged
images
Curves inward
Virtual
images
Reduced
images
Curves
outward
Quick Lab – everyone go get a spoon!!!
Situation 1
Grab a spoon and hold it close to your face so the back side
of the spoon is toward your face, as shown in Figure 33.1.4.
Observe your image in the spoon and slowly move the spoon
away from your face. What do you observe? Is the spoon
acting as a concave or convex mirror in this situation?
Position
yourself on
this side of a
spoon
Fig 33.1.4
Convex Versus Concave
When the back side of the spoon is facing you, it is acting as a
convex mirror.
•The image in the convex mirror is upright and always a virtual image.
•A virtual image cannot be reflected back onto a screen.
Quick lab - Situation 2
Now, repeat the same procedure but flip the spoon so the
scoop part is facing you, as shown in Figure 33.1.5. Hold the
spoon really close to your eye and slowly move the spoon
away from your face. What do you observe? Is the spoon
acting as a concave or convex mirror in this situation?
Position
yourself on
this side of a
spoon
Fig 33.1.5
When the front side of the spoon is facing you, it is acting as
a concave mirror.
•The image in a concave mirror is upright and virtual when
the object is inside the focal point.
•When the object is outside the focal point, the image
becomes a real image and it is inverted.
•A real image means that a screen could be placed there and
the image would appear.
•An inverted image has been flipped upside down.
•You may have noticed that sometimes the image in the
spoon seemed to get larger or smaller. If an image gets
larger, it will have a positive magnification and if the image
gets smaller it will have a negative magnification.
Refraction of Light
(not reflection)
When light rays enter a medium at an angle, the change in
speed causes the rays to bend or change direction.
- Refraction and Lenses
Lenses
A lens is a curved piece of glass or other transparent material.
Lenses
An object’s position relative to the focal point determines
whether a convex lens forms a real image or a virtual image.
Lenses
A concave lens can produce only virtual images because
parallel light rays passing through the lens never meet.
Asking Questions
Question
Answer
When does refraction
occur?
When light rays enter a
medium at an angle
What are the types of
lenses?
Concave and convex
lenses
Light entering the eye first enters through the cornea, where it is refracted and
begins to focus the light through the pupil. The pupil will expand during times of low
light in order to allow more light to enter the eye. During times of bright light it will
contract. When the pupil contracts, the iris gets larger and when the pupil expands,
the iris gets smaller. After light passes through the pupil it then enters the convex
lens in your eye. This lens focuses the light onto the light sensor cells on the back of
your eye called rods and cones which are collected at the retina. The area where
the nerve endings come together to form the optic nerve create a blind spot.
Correcting Vision
Concave lenses are used to correct nearsightedness.
Convex lenses are used to correct farsightedness.
Eye Glasses
Sequencing
How You See Objects
Light enters the eye.
Light focuses on the retina.
An image forms.
Rods and cones send signals to the brain.
- Using Light
Optical Instruments
A telescope forms enlarged images of distant objects.
Telescopes use lenses or mirrors to collect and focus
light from distant objects.
- Using Light
Optical Instruments
A telescope forms enlarged images of distant objects.
Telescopes use lenses or mirrors to collect and focus
light from distant objects.
Optical Instruments
A microscope uses a combination of lenses to produce and
magnify an image.
- Using Light
Optical Instruments
The lens of the camera focuses light to form a real, upsidedown image on film in the back of the camera.
- Using Light
Lasers
Laser light consists of light waves that all have
the same wavelength, or color. The waves are
coherent, or in step.
- Using Light
Optical Fibers
The floodlight in the swimming pool gives off light rays that
travel to the surface. If the angle of incidence is great
enough, a light ray is completely reflected back into the
water. This complete reflection of light by the inside surface
of a medium is called total internal reflection.
- Using Light
Optical Fibers
Optical fibers can carry a laser
beam for long distances
because the beam stays totally
inside the fiber as it travels.