Geometrical optics
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Transcript Geometrical optics
Geometrical optics
The Sun is our natural
source of light.
Objects such as the
sun, a light bulb, a
fire, which give off
their own light are
called luminous.
Objects which can
only be seen when
light falls on them are
called non-luminous
objects.
Geometrical optics is
the study of how light
rays interact with
matter.
In order to understand
how light behaves it is
necessary to
understand some of
the properties of light.
Light travels in straight lines.
Light rays, beams.
The fact that light
travels in straight lines
explains the formation
of shadows as well as
the fact that we are
unable to see around
corners.
In our study of optics
we represent a ray of
light as an arrow.
Several arrows drawn
together represent a
beam of light.
Parallel Beam
Converging Beam
Diverging Beam
Reflection of Light
When light strikes an
object some of the
light is absorbed and
some bounces back.
The bouncing of light
off an object is known
as reflection.
The reflection of light
can either be regular
reflection or diffuse
reflection.
Diffuse reflection!
Most objects reflect
light in a diffuse
manner which means
that the light is
reflected in all
directions.
Such an object can be
seen when viewed
from any direction.
Light rays
Object
Objects which are perfectly
smooth or polished will
reflect light in a regular
Regular reflection!
manner.
Light which is reflected in
Light rays
this way will bounce back
from an object at one
particular angle or in one
particular direction.
Objects which reflect light
Object
in a regular manner are
general called mirrors.
Mirrors can either be flat
(plane) or curved
(spherical).
Ray diagrams.
We can use simple
diagrams to explain
how light is reflected,
called ray diagrams.
Ray diagrams help us
to describe how
images are formed by
both plane and
spherical mirrors.
The ray of light striking the mirror is called
the incident ray
The ray of light reflected is called the
reflected ray.
The point where the incident ray strikes the
mirror is called the point of incidence.
A line drawn at right angles to the mirror at the
point of incidence is called the normal, ‘N’.
The angle between the incident ray and the
normal is called the angle of incidence, ‘i’..
The angle between the reflected ray and the
normal is called the angle of reflection, ‘r’.
The Laws of Reflection
When light is reflected
from the surface f a
plane mirror;
The incident ray, the
normal and he
reflected ray all lie in
the same plane.
The angle of
incidence ‘i’ is equal
to the angle of
reflection ‘r’.
N
Reflected ray
Incident ray
i
r
i=r
Images formed by plane mirrors.
The image formed by
Object
Virtual Image
a plane mirror will be
1. A virtual image
2. The same distance
behind the mirror as
the object is in front
of the mirror
3. Laterally inverted,
(reversed left to
A virtual image is one formed
right).
by the apparent intersection
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of light rays.
Uses of plane mirrors.
Because of ‘lateral
inversion’, the
practical uses of plane
are limited.
Emergency vehicles
will print names right
to left so that when
viewed in a rear view
mirror they can be
read properly, i.e. left
to right.
Plane mirrors are used to
view one own reflection.
The periscope.
The periscope is an
instrument used to
view around obstacles.
Two plane mirrors are
placed at 45º and used
to reflect light in a
regular manner.
Submarines, sports
events.
Locating images produced by
plane mirrors.
The apparent movement of one object relative
to another due to the motion of the observer is
called parallax.
The object which is farthest away moves with
the observer.
No parallax occurs if the two objects are at the
same point.
The method of no parallax is used to locate
the image formed by a plane mirror.