As we have discussed before, we will see theory of the Light chapter in this blog
Laws:
Laws of refraction :
first law: The angle of incidence is equal to the angle of reflection
second law: The incident ray, the normal to the mirror at the point of incidence and the reflected ray, all lie in the same plane.
first law: The incident ray, the refracted ray and the normal to the interface of two transparent media at the point of incidence, all lie in the same plane.
second law: The ratio of sine of angle of incidence to the sine of angle of refraction is a constant, for the light of a given color and for the given pair of media.
This law is also known as Snell’s law of refraction.
Definitions :
- Centre of curvature: The reflecting surface of a spherical mirror forms a part of a sphere. This sphere has a Centre. This point is called the Centre of curvature of the spherical mirror.
- Pole: The Centre of the reflecting surface of a spherical mirror is a point called the pole:
- Principle axis: Imagine a straight line passing through the pole and the centre of curvature of a spherical mirror. This line is called the principal axis.
- Radius of curvature: The radius of the sphere of which the reflecting surface of a spherical mirror forms a part, is called the radius of curvature of the mirror.
- Aperture: The diameter of the reflecting surface of spherical mirror is called its aperture
- Principle focus: A number of rays parallel to the principal axis are falling on a concave mirror, the reflected rays are all intersecting at a point on the principal axis of the mirror. This point is called the principal focus of the concave mirror and The reflected rays appear to come from a point on the principal axis. This point is called the principal focus of the convex mirror.
- Focal length: The distance between the pole and the principal focus of a spherical mirror is called the focal length.
- Refraction: When travelling obliquely from one medium to another, the direction of propagation of light in the second medium changes. This phenomenon is known as refraction of light.
- Refractive index ( relative): The refractive index of medium 2 with respect to medium 1 is given by the ratio of the speed of light in medium 1 and the speed of light in medium 2.
- Absolute refractive index: If medium 1 is vacuum or air, then the refractive index of medium 2 is considered with respect to vacuum. This is called the absolute refractive index of the medium.
- Power of the lens: The power of a lens is defined as the reciprocal of its focal length.
|
Position of the object |
Position of the image |
Size of the image |
Nature of the image |
|
At infinity |
At F |
Highly diminished |
Real and inverted |
|
Beyond C |
Between C
and F |
Diminished |
Real and
inverted |
|
At F |
At C |
Same size |
Real and inverted |
|
Between C and F |
Beyond C |
Enlarged |
Real and
inverted |
|
At F |
At infinity |
Highly enlarged |
Real and inverted |
|
Between F and Pole |
Behind the
mirror |
Enlarged |
Virtual
and erect |
|
Position of the object |
Position of the image |
Size of the image |
Nature of the image |
|
At infinity |
At F |
Highly diminished |
Virtual and erect |
|
Between infinity and pole of the mirror |
Between F
and Pole |
Diminished |
Virtual
and erect |
|
Position of the object |
Position of the image |
Size of the image |
Nature of the image |
|
At infinity |
At F1 |
Highly diminished |
Virtual and erect |
|
Between infinity and the optical Centre of the lens |
Between F1
and O |
Diminished |
Virtual
and erect |
|
Position of the object |
Position of the image |
Size of the image |
Nature of the image |
|
At infinity |
At F2 |
Highly diminished |
Real and inverted |
|
Beyond 2F1 |
Between 2 F2
and F2 |
Diminished |
Real and
inverted |
|
At F1 |
At 2 F2 |
Same size |
Real and inverted |
|
Between 2F1 and F1 |
Beyond 2F2 |
Enlarged |
Real and
inverted |
|
At F1 |
At infinity |
Highly enlarged |
Real and inverted |
|
Between F1 and O |
On the same side of the object |
Enlarged |
Virtual
and erect |
- virtual and erect image
- laterally inverted
- same size as an object
- forms at same distance as an object
Uses of both types of lenses and mirrors.
Concave mirror- Dentist mirror, Solar furnace, Torch light, Head lights of vehicle, etc.
Convex mirror- Rear view mirror, security mirror outside the societies, etc.
Concave lens- Eye piece of camera, security lens on door, etc.
Convex lens- Microscope, telescope, Cameras, etc.
Difference between real image and virtual image
|
Real image |
Virtual image |
|
Actual intersection of
rays takes place |
Rays do not intersect |
|
Always inverted |
Always erect |
|
Can be formed on the
screen |
Cannot be formed the
screen |
|
Image forms in either in front of the mirror or on the other side of
object in the case of lens |
Image is
either formed behind the mirror or on the same side of the object in case of
lens |
