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Part 1 /2
Physics Ex-48
PART-1 /2
Study the terminology
of parabolic mirrors.
Light rays
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Physics Ex-48
RULES FOR DRAWING RAYS IN CURVED MIRRORS
A ray that is parallel to the principal axis is reflected through
the principal focus (F).
A ray passing through the principal focus (F) is reflected parallel
to the principal axis.
A ray passing through the center of curvature (C) is reflected
back along its own path.
Note that images have properties called "characteristics".
Image characteristics include:
Location of image (behind mirror or in front of mirror)
Size (magnification) of image (larger or smaller than object)
Attitude (whether the image is inverted or upright)
Reversed (whether the image is reversed left-to-right, "mirror image")
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Physics Ex-48
 CONCAVE MIRRORS
The characteristics of an image formed by a concave mirror depend
on the location of the object. As it turns out, there are six “strategic”
locations where an object may be placed. For each location, the
image will be formed at a different place and with different
characteristics. We will study the six different locations and label
them as CASE-1 to CASE-6.
Be sure to study
each case!
Case-1:
Case-2:
Case-3:
Case-4:
Object
Object
Object
Object
at infinity
just beyond C
at C (center of curvature)
between C and F
Case-5: Object at F (focal point)
Case-6: Object between F and V (within focal length)
6
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Physics Ex-47
In order to draw images formed by curved mirrors, remember that :
A ray parallel to the
principal axis is reflected
through the focal point (F).
V
Principal axis
C
F
Back of
mirror
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Physics Ex-47
In order to draw images formed by curved mirrors, remember that :
A ray that goes through the
focal point (F) is reflected
parallel to the principal axis.
V
Principal axis
C
F
Back of
mirror
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Physics Ex-47
In order to draw images formed by curved mirrors, remember that :
A ray that strikes the vertex (V)
is reflected like a plane mirror.
(Angle of incidence = Angle of reflection)
V
Principal axis
C
F
Back of
mirror
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Physics Ex-47
In order to draw images formed by curved mirrors, remember that :
A ray that goes through C
(the center of curvature) is reflected
back along its own path.
V
Principal axis
C
F
Back of
mirror
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Physics Ex-48
This distance is known as the “focal length” (f).
REMEMBER
f
The focal length (f) is
from the focal point (F)
to the vertex point (V).
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Physics Ex-48
Object at infinity
No image
Due to the great distance the object is from the mirror,
all rays arrive at the mirror parallel to the principal axis.
As a result, all rays focus at the focal point and no image
is formed.
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Physics Ex-48
Object just beyond C
Image is real,
between C and F,
inverted and reduced.
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Physics Ex-48
Object at C
Image is real,
located at C, inverted and
same height as object.
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Physics Ex-48
Object between C and F
Image is real,
located beyond C, inverted
and larger than the object.
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Physics Ex-48
Object at F
All rays are reflected
parallel and thus
no image is formed.
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Physics Ex-48
Object between F and V
(within the focal length)
Image is virtual,
located inside the mirror,
upright and larger than the object.
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Physics Ex-48
Object point
Such as
Incident ray
right here!
An object is placed in front
of a concave mirror.
Find the location and
characteristics of the image.
Object
C
C of an infinite
F number
Objects consist
ofcan
points.
Image
We
now draw the image.
Image point
Reflected
ray
And each point has an infinite
number
of rays
outwards.
Back radiating
of
mirror
Images also consist of an infinite number of points.
Where
the two
rays
meet
Since
wehas
are
given
thereflected
location
of the
the
object,
Each point on the
object
anot
corresponding
point on
image.
theselect
imageany
point
of the location.
object point.
we is
can
arbitrary
Step-1
Step-2
There are two steps in finding the image of a concave mirror.
Draw
a rayon
through
parallel
to
thethe
focal
principal
pointfind
and
axisits
In locating an image, we take one
point
the object
and
and
it reflect
it reflect
parallel
through
to thethe
principal
focal point.
axis.
corresponding point (location)make
on make
the
image
object.
Since the intersecting rays are both reflected rays,
image
real.
As shown above, we usuallythe
take
the is
(extreme)
top point
and find its corresponding point on the image object.
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Physics Ex-48
Convex mirrors produce
a very large field of view.
For convex mirrors, the image is always virtual,
always located inside the mirror,
always upright and always smaller than the object.
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Question-1
Physics Ex-48
State the rules for finding the image formed by a curved mirror.
1- A ray parallel to the principal axis is reflected through the
focal point (F).
2- A ray through the focal point (F) is reflected parallel to the
principal axis.
3- A ray through the center of curvature (C) is reflected back
along its own path.
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Question-2
Physics Ex-48
State four characteristics of images.
1- Type (real or virtual)
2- Location (distance from mirror)
3- Magnification (size)
4- Attitude (upright or inverted
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Question-3
Physics Ex-48
What is spherical aberration and how can it be eliminated?
A fuzzy image produced by the fact that parallel rays do not pass
through the focal point (F).
It can be eliminated by making the mirror parabolic rather than
spherical.
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Question-4
Physics Ex-48
The diagram below displays a concave mirror and a beam of light
striking the mirror. Label each part.
Focal plane
Concave mirror
Principal axis
Vertex (V)
Reflected ray
Focal point (F)
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Question-5
Physics Ex-48
The diagram below illustrates the image of an object produced
by a concave mirror. Label the incident ray, the reflected ray
and the extended ray.
Extended ray
Incident ray
Reflected ray
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Physics Ex-48
Question-6
For each concave mirror below, draw the image.
a)
Image
Image is real
(formed by reflected rays)
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Physics Ex-48
Question-6
For each concave mirror below, draw the image.
b)
Image
Image is real
(formed by reflected rays)
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Physics Ex-48
Question-6
For each concave mirror below, draw the image.
c)
Image
Image is real
(formed by reflected rays)
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Physics Ex-48
Question-6
For each concave mirror below, draw the image.
d)
Image
Image is virtual
(formed by extended rays)
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Physics Ex-48
Question-7
The diagram below shows an illuminated object and its virtual
image in a concave parabolic mirror.
Determine the location of the focal point (F).
F
C
REMINDER
The focal point (F) is half
the radius of curvature (C).
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Physics Ex-48
Question-8
The diagram below shows an object in front of a convex parabolic
mirror. Draw the image.
Image is virtual,
upright and smaller
than the object.
Image
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Question-9
Physics Ex-48
Where must an object be placed in front of a concave mirror
so as to form an image that is:
a) Smaller than object?
Just
beyond the center of curvature (C).
____________________________________
b) Inverted?
Beyond
the focal point (F).
____________________________________
c) Virtual?
Within
the focal length (f).
____________________________________
d) Inverted and magnified ?
Between C and F.
____________________________________
e) Same height as object?
At
the center of curvature (C).
____________________________________
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Question-10
Physics Ex-48
Consider a convex mirror, where must an object be placed
so as produce a real image?
Impossible, convex mirrors do not produce real images.
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Question-11
Physics Ex-48
State the properties of a virtual image.
A virtual image is formed by extended rays.
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Question-12
Physics Ex-48
In what important way does a virtual image differ from
a real image?
In the fact that a virtual image cannot be projected onto a screen.
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Physics Ex-48
Question-13
Consider an object placed in front of a concave mirror. Which one
of the following statements correctly describes its image?
Back
Image
A) It is in front of the mirror, inverted, real and smaller than
the object.
B) It is behind the mirror, upright, virtual, and smaller than
the object.
C) It is in front of the mirror, upright, real and smaller than
the object.
D) It is behind the mirror, upright, virtual and larger than
the object.
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Physics Ex-48
Question-18
An object is placed in front of a convex mirror as illustrated below.
Draw and label the light rays necessary to locate the image.
Incident ray
Image
Image is virtual, upright and reduced.
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