science project, plane mirrors, properties, examples, activities, physics

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PRODUCERS :
SEHAJPAL SINGH &
MANJOT SINGH
BUDHA DAL PUBLIC
SCHOOL, Patiala,India
Class Xth (2010-11)

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3. In this section we deal with plane mirrors. These are
mirrors that are flat. In most cases the mirrors we see
are pieces of glass with a silvered coating on the back,
while in some cases the silvered coating may be on the
front of the glass. Such a mirror is referred to as a
front-surface mirror. Other objects behave like mirrors
including smooth surfaces of :

7. What are the rules by which mirrors
operate when light strikes them?
When an ordinary object is placed in front of
a plane mirror, it is sending light rays out
from itself in all directions, either by
emission or by reflection. This is shown
here:

8. Therefore the light rays that strike the mirror will be
doing so from a wide variety of angles. What is the
pattern for light's reflection and how does it depend on
angle?
In Reflection we picture a line perpendicular to the
mirror at the point of reflection. This is called
the Normal. (Remember when we used the normal to
define the angles in Snell's Law.) The Law of
Reflection states that light reflecting from
a plane mirror forms an angle to the
NORMAL equal to the angle between the
normal and the incident light.

9. When an object is placed in front of a mirror,
two different observers appear to see an image
of the object in different places. The light,
however, travels from the single object to the
mirror and then to the respective observers. The
manner in which it reflects must meet the
conditions stated on the previously.
Notice how the light reflects from
the smooth surface of the mirror,
creating congruent or equal angles
to the normal at each place it
strikes the mirror. The two
observers only see light when it
has been reflected from the mirror
in the proper manner .

10. What is the nature of the light at
the image location?
 In fact, there is no light there. This is only the
apparent source of the light so it is referred to as
a virtual image. Virtual images are ones that are
not formed by putting the light rays together, but
only appear to exist as the apparent source of the
light rays.

11. GEOMETRY:
What is the geometry of the plane mirror's image? In
the next series of drawings we can follow the
geometric proof of where the image is located.
Use the vertical angle theorem to establish other
angles congruent to the ones you had seen in the last
drawing.

12. And use the complementary angle theorem to
establish two more sets of congruent angles.
Now, using the logic of ASA, the two triangles formed, one on
the object side of the mirror, the other one behind the mirror,
can be proven congruent
Thus the triangle "behind" the mirror is the same size and shape
as the triangle in front.

13. The object and its virtual image can be joined by a line which is
perpendicular to the mirror, forming altitudes for the two
triangles.
Now because the two perpendicular lines are altitudes for
triangles that are exactly the same shape and size, their lengths
must also be the same. This leads us to the following conclusion:
The image formed by a plane mirror will be as far behind the
mirror as the object is in front of it. A line joining the two will be
perpendicular to the mirror.

14. The relationship between the number of images and the
angle between the mirrors is
No. of images = 360°
angle between mirrors
1.
We can change the number of images
produced by two mirrors by changing the
angle between them .
The relationship between the number of
images and the angle between the mirrors is
No. of images = 360°
1
angle between mirrors
We will proof it by doing an ACTIVITY…

15. WHAT WAS REALLY HAPPENING WHILE
DOING THE ACTIVITY ???
Multiple reflections are difficult to
understand and visualize. If you have one
flat mirror, light
from the object will reflect off the mirror
once and leave the system. When you have
more than one mirror, you can create
multiple reflections. These multiple
reflections can lead to multiple images.
I
1
I
2
OBJECT
I1
I2
Consider the two mirrors (solid lines) shown
at right at an angle of 120 degrees to each
other. The object is a small ball. The images,
I1 and I2, form exactly on the opposite side
of each mirror, the same distance from the
mirror, just as you would expect for
reflection from a single mirror. The two
mirrors each yield an image.
You will also notice that I1 and I2 lie equal

16. WHAT WAS REALLY HAPPENING WHILE
DOING THE ACTIVITY???
When the angle is decreased, more
reflections will occur. Let’s look at two
mirrors that are perpendicular to each
other. One image will form from a
single reflection from each mirror. You
might recall from “Right is Right, or is
it Left?” that perpendicular mirrors
yield two reflections. These two
reflections create the third image, I3.
You can see these reflections by looking
into the mirror as shown. .