Optics I

Laws of Reflection
Reflection At Spherical Mirrors
Image Formation By Concave Mirror & Convex Mirror
When light is incident on a surface, it partly goes back (reflected), partly gets absorbed in the surface and the rest may transmit through it.
In practice, mirrors, formed by depositing a thin silver layer on one side of the glass sheet are used to reflect the light.

The phenomenon of change in the path of light without any change in the medium is termed as reflection of light.

Angle of incidence: The angle which the incident ray makes with the normal at the point of incidence is called the angle of incidence. It is generally denoted by ' i '.

Angle of reflection: The angle which the reflected ray makes with the normal at the point of incidence is called the angle reflection. It is generally denoted by ' r '.

Law of Reflection





 #              that is angle of incidence is equal to angle of reflection.

# Incident ray , reflected ray and normal to the mirror, all lie in the same plane.

Reflection At Spherical Mirrors




Some Important Definations

(1) Spherical Mirrors:A spherical mirror is a part of a hollow sphere or a spherical surface. They are classified as concave or convex according to the reflecting surface being concaev or convex respectively

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(2) Radius of Curvature(R):Radius of curvature is the radius R of the sphere of which the mirror forms a part.









(3)Pole or Vertex:The geometrical center of the spherical mirror is called the pole or vertex if the mirror.

(4) Centre of curvature: The centre of curvature of spherical mirror is the centre of the sphere of which the mirror forms a part. It is represented by C.

(5) Principal axis: The line CP joinig the pole and the center of curvature of the spherical mirror is called principal axis.

(6)Focus (F): The point F is called the focus of the spherical mirror.

(7)Focal Length(f): Focal length is the distance PF between the pole and focus along the principal axis.

(8)Aperture: The diameter of the spherical mirror is called the aperture or linear aperture of the mirror.

Relation between radius of curvature (R) and focal length (f)

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The magnitude of the focal length in spherical mirrors is half the radius of curvature,


Image Formation By Concave Mirror

(i) When the object is at infinity


(ii) When the object lies beyond C (i.e.,between infinity and C)

(iii) When the object lies at C

(iv) When the object lies between F and C

(v) When the object at F

(vi) When the object lies between P and F

Image Formation By Convex Mirror

(i) When the object is at infinity

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Mirror Formula





Object distance, image distance and focal length in spherical mirrors are related by he equation:

Linear Magnification





Linear magnification or simply magnification of a spherical mirror is the ratio of the size of the image formed by the mirror to the size of the object. It is denoted by m .
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