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Optics
What is Optics?
– the study of how light behaves, or
– the collection and use of light to create images.
• Optical system: Collects light and uses
refraction and reflection to form an image
– lenses-which refract (bend) light
– mirrors - which reflect (bounce) light
How can it bend?
• Light always travels in a straight line, but if
it encounters another object or medium, it
can change directions.
– when light is bent so that it comes together it is
called converging
– when light is bent so that it spreads apart it is
called diverging
Light Rays
• an imaginary arrow that follows a single
beam of light
Bending of light that occurs when light crosses a boundary between
two different substances.
Objects or waves “bounce” off a surface
Images
• A place where many light rays from the same point
on an object meet together again in a point called the
focus, or focal point.
– They are “pictures” of objects
 Two types of images:
– virtual - "not real" - the image only seems to be
where it is; cannot be projected onto a screen
– real -can be projected onto a screen, because the
light actually passes through the point where the
image appears
Optical Devices
• Most optical devices have two functions:
1. They collect light rays
2. They bend the collected rays to form an
image.
• To illustrate how an optical device works,
we draw ray diagrams to trace several light
rays through a system
The Ray Diagram
Two rules:
1. In through the focal point, out parallel
2. In parallel, out through the focal point.
Ray diagrams
• Help answer questions like:
–
–
–
–
Where is the focal point (or is there one)?
Will the image be magnified or reduced in size?
Will the image be upside down or right side up?
Will the image be inverted left or right?
Law of Reflection
Light rays bounce off a mirror at the same angle at
which they arrive.
Three Types of Mirrors
–plane
- flat
– image is right-side-up, the same size and
virtual
–concave - curved inward; creates a focal
point
–if the object is placed at the focal point, the
image
is inverted, smaller, and real
–if the object is placed closer to the mirror the
image is larger and virtual
–convex - curved outward
–the image is right-side-up, smaller, and virtual
Lenses

a transparent material that
refracts light

usually made of glass or
plastic with one or two
curved surfaces
Bending of light that occurs when light crosses a boundary
between two different substances.
Two types of lenses:
–convex
converging
–- thicker in the center than at the edges
–converges the light rays (forms a focal point)
–forms a real image (magnifies objects)
–corrects farsightedness
–concave diverging
–thicker at the edges and thinner in the center
–diverges the light rays
–images are smaller and right-side-up
–forms virtual images
–corrects nearsightedness