Optical Systems
Make use of Mirrors and Lenses!
Sir Isaac Newton – developed the particle model of
light- thought that light was made of tiny particles that
travelled in a straight line until they entered the eye.
•
Light is made up of both the particle model and the
wave model = the ray model of light.
•
Light is represented as a straight line showing
direction of travel
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What you see depends on the amount of light
available
In dim light you can no longer tell colours apart
The type of matter in an object determines the
amount of light it absorbs, reflects, and transmits
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• Light can pass through freely, only a small
amount
of light is absorbed and reflected
(Example: air, water, and glass)
•
Most light rays get through but they are
scattered
in all directions (Example: frosted glass)
• Prevents light from passing through
(Example: cardboard)
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You can predict shadows using the ray model of light
Size of shadows are related to distance from the light
source
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• To act like a mirror a material must: have a
smooth surface compared to the wavelength of
the light striking the surface
• If the surface is uneven then the rays will be
reflected at different angles
• Incoming ray = incident ray
• Ray that bounces off = reflected ray
• Right angle between the two rays
• Normal line is at right angles to the reflecting surface
• Angle of incidence (i) = Angle of reflection (r)
= Law of Reflection
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• When light is bent, when it changes speed from one
medium into another, it is called refraction
• When light moves between air and glass it slows
down because glass is more dense
• Angle of refraction = angle of a ray of light emerging
from the boundary between two materials it is
measured between the normal and the refracted ray
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Can occur when light
passes through air of
different temperatures
Warm air is less dense
than cold air
Results in a mirage
Textbook questions
Page 181
Questions # 1-7, 9
There will be a homework check! 
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Plane mirror – flat
smooth mirror, where
you appear to be the
same distance behind
the mirror as you are
in front of the mirror
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• The reflected light that bounces off the
mirror is doing so in all directions but only
certain ones reach the pupil of our eye
• Our brain knows that light travels in a
straight line so it interprets the image coming
from behind the mirror
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Both will be the same
when using a plane
mirror
A plane mirror will
produce an image that
has the same orientation
as the object (both
upright) but left and right
will appear reversed
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• Curve inwards, and reflect light rays to form
images
• Causes light rays to converge and meet at a focal
point
• Image produced depends on the distance form
the focal point
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• Image will be small and upside down as you
get closer the image will get larger to a point
where it is between the mirror and the focal
point where the image will appear upright (see
p.185)
• Used for flashlights, headlights, lighthouses,
telescopes, and make-up mirrors
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• Curves outward, opposite to concave,
diverging rays are given off
• Image is always upright and smaller then the
actual image
Main Characteristics:
1. Objects appear to be smaller than they are
2.
More objects can be seen than in a plane
mirror of the same size
 • Used for security mirrors, on car mirrors
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Textbook questions
 Page 189
 Questions #1-5
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• Lens = a curved piece of transparent material
that refracts light rays to either diverge or
converge
• Can be either convex or concave
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• Are thinner in the middle than the edge
• Makes light rays diverge and won’t meet at a
focal point
• Image is always upright and smaller than the
actual object
• Uses: glasses, telescopes
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Thicker in the middle
Light rays converge meeting at a focal point
behind the lens
Image depends on the distance between the
lens and the object
Uses: magnifying glasses, cameras, telescopes,
microscopes, our eye
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• Focal length = distance between the
lens/mirror and the focal point
• This has been mathematically determined for
distance of object
Distance of Object from Lens
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More than 2 focal lengths
Between 1 and 2 focal lengths
Object at focal length
Less than 1 focal length
Type of Image Formed
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Smaller, inverted
Larger, inverted
No image
Larger, upright
Textbook Questions
Page 197
Questions # 2-7, 11