Physics CH # 13

1. Incident Ray:The ray that strikes the surface of the medium is known as Incident Ray
2. Reflected Ray:The ray that is sent back into the same medium after reflection is known as reflected ray.
3. Plane Mirror:A flat smooth reflecting surface, which shows regular reflection is known as plane mirror.
4. Normal:Perpendicular line on the reflecting surface is known as normal.
5. Pole:The centre of the spherical mirror is called pole.
6. Angle Of Incidence:The angle subtended by the incident ray to the normal is known as angle of incidence.
7. Angle Of Reflection:The angle subtended by the reflected ray to the normal is known as angle of reflection.
8. Center Of Reflection:The center of the hollow sphere of which the mirror is a part is called center of curvature.
9. Principle Axis:The straight line passing through center of curvature nad the pole is known as principle axis.
10. Principle Focus:The ray coming parallel to principal axis after converges to or diverges from a point, which is called principle focus.
11. Focal Length:The distance between the principle focus and pole of the mirror is called Focal Length.
12. Radius Of Curvature:The distance between the center of curvature and the pole is called radius of curvature.
13. Real Image:The image that can be seen on a screen is known as a real image.
14. Virtual Image:The image that cannot be seen on a screen is known as a virtual image.
15. Magnification:The ratio between the image height and object height is known as magnification.or
The ratio between the image distance to the object distance is known as magnification.
Reflection Of Light:

“The process in which light striking the surface of another medium bounces back in the same medium is known as Reflection of Light.”
Laws Of Reflection:
1. The angle of reflection, is equal to the angle of incidence
2. The incident ray, reflected ray and normal, all lie in the same plane.
Kinds Of Reflection:
There are two types of Reflection:
1. Regular Reflection:
When parallel rays of light strike a surface and most of them are reflected in a same particular direction or same angle, they are said to be regularly reflected and the phenomenon is known as regular reflection.
Regular reflection occurs when parallel rays of light strike with an ideal smooth plane surface. In regular reflection parallel rays remain parallel after reflection.

2. Irregular Reflection:
When some rays of light strikes a surface and the reflected rays scatter in different directions, this type of reflection is called irregular reflection.
It occurs when parallel rays strike with an irregular rough surface. In this case rays does not remain parallel after reflection and they scattered.

Advantages Of Irregular Reflection:
  • Due to this reflection, sunlight reaches us before sunrise and persists for some time even after the sunset.
  • Due to this reflection we get sufficient light in our rooms and other places where sunlight do not reach directly.
  • Due to this reflection sunlight reaches to each of the leaves of a tree and photosynthesis takes place on large scale.
  • Due to this reflection, we can see luminous objects.
Image Formed By A Plane Mirror:
Consider a mirror MM’, A is an object. Consider that a point A lies on the tip of the object. From A as ray travels and strikes mirror and reflect back to the eye, they appear to come back. From Point A’ as shown in the figure. Hence A’ is the image of A. Similarly, infinite points lying an object produces infinite images of points and complete image of an object is formed.
Characteristics Of Image Formed By A Plane Mirror:
  • Image is same in size as that of the object.
  • The distance of object and image are equal from the mirror.
  • The image formed is virtual and inverted.
Spherical Mirrors:
“A spherical mirror is a section of a of a hollow sphere.”
Types Of Spherical Mirrors:
There are two types of spherical mirror:
1. Concave Mirror (Converging Mirror)
2. Convex Mirror (Diverging Mirror)

1. Concave Mirror:
“The spherical mirror in which inner side of the surface is polished for reflection is called a concave mirror.”
  • The bulging side is polished.
  • Reflection occurs from its hollow side.
  • They converge the parallel rays at a point.
  • They can form real and imaginary, both types of images.
2. Convex Mirror:
“The spherical mirror in which inner side of the surface is polished for reflection is called concave mirror.”
  • The bulging side is polished.
  • Reflection occurs from its hollow side.
  • They converge the parallel rays at a point.
  • They can form real and imaginary, both type of images.
Formation Of Image By Concave Mirrors
There are six cases to form an image by concave mirror.
1. Object Beyond C:

If The object is placed beyond C, rays coming from the object are not parallel. They meet after reflection between the focus and center of curvature. Therefore, image is formed between the focus and center of curvature.

Details of Image
  • Formed between F and C.
  • Small in size.
  • Real
  • Inverted
2. Object At Center Of Curvature ‘C’:
When object is placed at the centre of curvature, the image formed at the same place.

Details of Image
  • Formed at C
  • Equal in size
  • Real
  • Inverted
3. Object Between F And C:

When the object is placed between the focus and Centre of curvature, the image is formed beyond the centre of curvature.

Details of Image
  • Formed beyond C.
  • Large in size.
  • Real
  • Inverted
4. Object Between P And F:

For locating object between pole and focus the rays reflected do not meet because they diverge. But they meet backward. So, the image is formed backward or behind the mirror.

Details of Image
  • Formed behind the mirror.
  • Large in size
  • Virtual
  • Erect
Uses Of Spherical Mirror:
Spherical mirrors are used in several places. Some of them are given below:
Shaving: A concave mirror is used to enlarge the image.
Microscope: A convex mirror is used for magnification in a microscope.
Telescope: The convex mirror is used.
In Searchlights and Headlights: Concave mirror is used to form the rays in searchlights and headlights, used for different purposes.
For Rear View: The convex mirror is used in automobiles.
In Medical Examination (Opthalmoscope): Doctors use concave mirror for the examination of ear, nose, throat and eyes of patients.
Mirror Equation:
The characteristics and location of an image formed by a spherical mirror can be determined from an equation which is called spherical mirror formula.

To derive concave mirror formula consider fig. where an object OA, is placed in front of a concave mirror. A ray of light starting from the end point A of the object and moving parallel to the principal axis strikes the mirror at the point E. it is reflected at E and passes through the principal focus F. A second ray also starting from A falls on the mirror at pole P. it is reflected by making an angle of reflection equal to the angle of incidence and intersects the first reflected ray at point B i. e., . Thus, point B is the real image of point A.

Generally, the distance of the object from the mirror is denoted by P and that of image as q. focal length of the mirror is denoted by f.
Therefore, the above equation can be written in the following manner:


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