In this post i will tell you what is light?, reflection of light, laws of reflection, image formed by plane mirror, Scattering of Light, Reflection of light, number of images, spherical mirror, centre of curvature, radius of curvature, radius of light, principle axis, aperture, principal focus, focal length (f), mirror formula, linear magnification, paraxial rays, light formula etc..
Contents
What is light -
Light is a form of energy
which is also called radiation. All sources of light emit radiation. "The
radiation that senses our eyes is called 'light'. As we know that when an
object is radiated then it is reflected on our eyes and then we see that object
in real The same radiation is called light. If we talk about the speed of
light, the speed of light is different in different mediums.
When the light rays are incident on an object, they are reflected, then reach to eyes and thus the object becomes visible.
Light is the principal means by which we gain knowledge of the world. Consequently the nature of the history of science. Electromagnetic radiation with wavelength in the range of about 4000Ä‚ to 7000Ä‚, to which eye is sensitive is called light.
When the light rays are incident on an object, they are reflected, then reach to eyes and thus the object becomes visible.
Light is the principal means by which we gain knowledge of the world. Consequently the nature of the history of science. Electromagnetic radiation with wavelength in the range of about 4000Ä‚ to 7000Ä‚, to which eye is sensitive is called light.
Medium
|
Speed of Light |
·
Exports
|
8
3 X 10
|
·
Glass
|
8
2 X 10
|
·
Water
|
8
2.25 X 10
|
·
Turpentine Oil
|
8
2.04 X 10
|
NOTE
\
It takes an average of 500 seconds for the light
to reach the Earth from the Sun. Similarly, it takes 1.24 seconds for the
light from the Moon to reach the Earth.
|
Scattering of Light
When light passes through a medium which contains very small particles of dust and other matter, light is transmitted in all directions by these particles. This phenomenon is called scattering of light.
Reflection of light
When the light falls on a polished spinning rhythm, most of it returns back. And the reflection of light, that is, the action of returning light after reflecting on a face glass, is called reflection of light.
"When a beam of light is incident on a polished interface, is thrown back in same medium. This phenomenon is called reflection.
In reflection the frequency, speed and wavelength do not change, but a phase change may occur depending on the nature of reflecting surface.
Experimentally it is found that the rays corresponding to the incident and reflected waves make equal angles with the normal to the surface. Thus, the two laws of reflection can be summarized as under:
"When a beam of light is incident on a polished interface, is thrown back in same medium. This phenomenon is called reflection.
In reflection the frequency, speed and wavelength do not change, but a phase change may occur depending on the nature of reflecting surface.
Experimentally it is found that the rays corresponding to the incident and reflected waves make equal angles with the normal to the surface. Thus, the two laws of reflection can be summarized as under:
Law of reflection |
|
1
|
The angle of reflection is always equal to
the angle of incidence. ∠i = ∠r
|
2
|
The incident ray, the normal at the incident
point and the returning ray are all in the same rhythm.
 |
Image
If rays of light move from some point of the object to another point after reflection, or appear to be coming from another point, then this second point is called the reflection of the first point.
Real Image |
Virtual Image |
If the light
rays moving from a point object actually meet at a point after reflection,
then this point is called the actual image of the point. These images are
inverted and can be taken on screen.
|
If the
light rays moving from a point of view appear to come from some other point
after reflection, then this point is called a virtual image of the point
object. They are always straight. Can't get them on screen
|
Image formed by plane mirror
(i) It is virtual, erect and of the same size as that of the
size of the object.
(ii) It is laterally inverted i.e right side of the same
size as the size of the object appears as the left side of the image and vice
versa.
(iii) It is at the same distance behind the mirror as the
object is in front of the mirror.
The radius of curvature (R) and hence focal length of plane
mirror is infinite.
The power of plane mirror is zero.
The number of images
of an object placed between two mirrors inclined at an angle () is given by
N= 360 / 0
-1, if 360/0 is even integer
N = 360 /0, if
360/0 is odd integer
The size of the plane mirror to produce to produce full size
image of a person standing in front of it = ½ x height of the person.
Spherical mirror is
a part of spherical reflecting surface.
Centre of curvature
is the centre of a hollow sphere of which the spherical mirror forms a part.
Radius of curvature
is the radius of a hollow sphere of which the spherical mirror forms a part.
Pole is the
centre of the spherical mirror.
Principle axis is
the line joining the center of curvature and the pole of the mirror.
Aperture is the
diameter of the spherical mirror.
Principal focus
is the point on the principal axis of the spherical mirror where the rays of
light parallel to the principal axis meet or appear to meet after reflection
from the mirror.
Focal length (f)
is the distance between the pole and principal focus of the mirror.
R = 2F or
F = R/2
Mirror formula :
The relation between object distance, image distance and focal length of the
mirror is called mirror formula
1/u + 1/v = 1/f
Linear magnification:
The ratio of size of image to the size of object.
m= I/O = -v/u =
f-v/ f = f/ f-u
Linear
magnification may be positive or negative
(i) m= +ve, If object and image both are upright
or if object is to the left side of the spherical mirror and image to the right
side ( or image is virtual)
(ii) m= -ve if object is upright and image is
inverted ( or image is real).
(iii) m= +1, if O=I
Paraxial rays:
The rays of light which are parallel and travel close to the principal axis of
the mirror.
Marginal rays:
The rays of light which are parallel and travel far away from the principal
axis of The mirror.
Spherical Aberration:
The inability of the spherical mirror to bring all the rays of a beam of light
falling on it to a focus it to a focus is called spherical aberration. Spherical
A berration can be eliminated by using a paraboloid mirror.
Paraboloid mirrors
are used in search lights torches, head lights of vehicles etc.
Convex mirror is used as a rear view mirror and hence known
as driver’s mirror.
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