Download Optics

Light
In this Unit you will learn:
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Light is form of energy
Properties of light
Laws of reflection reflection
Understand how to locate an image by no parallax
Lateral inversion
How images are formed in plane mirrors
Uses of plane mirrors
Keywords
reflection
No parallax normal
Light ray
Diffuse
reflection
Ange of
incidence
Virtual
image
Lateral
inversion
Regular
reflection
Angle of
reflection
Convergin
g ray
periscope
nonluminous
Incident
ray
Energy
luminous
Reflected
ray
Diverging
ray
Light is form of energy
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Light can do work eg.
Crookes radiometer
Light can be converted
to other forms of energy
e.g. Solar cell, light to
electricity. (show demo
model of this)
Other forms of energy
can be converted to light
e.g. Fire.
Part 2 – Properties of Light
Light travels in straight lines:
Laser
Light travels VERY FAST – around
300,000 kilometres per second.
At this speed it can
go around the world 8
times in one second.
Light travels much faster than sound. For example:
1) Thunder and lightning
start at the same time,
but we will see the
lightning first.
2) When a starting pistol
is fired we see the
smoke first and then
hear the bang.
We see things because they
reflect light into our eyes:
Homework
Luminous and non-luminous objects
A luminous object is one that produces light.
A non-luminous object is one that reflects light.
Name 3 luminous sources of light and 3 reflectors
Luminous objects
Reflectors
Shadows
Shadows are places where light is “blocked”:
Rays of light
Properties of Light summary
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Light is a form of energy
Light travels in straight lines
Light travels much faster than sound
We see things because they reflect light
into our eyes
Shadows are formed when light is blocked
by an object
Reflection
The bouncing of light of an object is called reflection
A straight líne showing the direction in which the light
is travelling is called a light ray
Beams of light can be coverging, diverging or parallel.
Clear vs. Diffuse Reflection
Smooth, shiny surfaces
have a clear reflection:
Rough, dull surfaces have
a diffuse reflection.
Diffuse reflection is when
light is scattered in
different directions
Reflection
Reflection from a plane mirror:
Normal
Reflected ray
Incident ray
Angle of
incidence
Angle of
reflection
Mirror
The Laws of Reflection
Incident ray, reflected ray and normal lie
on the same plane
Angle of incidence = Angle of reflection
In other words, light gets reflected (bounced) from a
surface at ____ _____ angle it hits it.
The
same !!!
Normal
How an Image is formed in a plane mirror
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The image is located ón the perpendicular form
the object to the mirror.
The image is the sames distance behind the mirror
as the object is in front of the mirror.
Experiments
1) To demonstrate the laws of reflection
using a plane mirror.
2)To locate an image in a plane mirror the
method of no parallax
Lateral Inversion
Lateral inversion is where the left of an object appears to the right
image and vice versa.
Real and Virtual images
A virtual image is an image formed by th apparent intersection
of light rays.
Use of plane mirrors
Two examples:
1) A periscope
2) looking at
yourself
Using no parallax to find an image
The apparent relative
motion of the two
pencils due to the
motion of the
observer is called
parallax
In diagram (b) there is
not apparent relative
motion of the pencils
due to the motion of
the observer, this is
called no parallax