Physics Made Simple : Spherical Mirrors

Spherical Mirrors:

A spherical mirror is a portion of the reflecting surface of a hollow sphere.

Spherical mirrors are of two types:

1.Concave Mirror:

In this mirror,the inner curved surface is reflecting.

2.Convex Mirrors:

In this mirror,the outer convex surface is reflecting.

Centre of Curvature:

The centre C of sphere of which a concave or a convex mirror is a part is known as Centre Of Curvature of the spherical mirror and the Radius Of Curvature R is the radius of the sphere.

Aperture:

The front section of spherical mirror is circular one and its diameter is known as the Aperture.

The Principal Focus:

Rays of light parallel to the principal axis after reflection from a concave mirror converge to focus on a point say F.This point is called as principal focus of the concave mirror.

In case of concave mirror,as the rays of light actually pass through this point,it is called as real focus.

In case of convex mirror,rays parallel to the principal axis after reflection appear to come from a point F situated behind the mirror.This point is called the principal focus of the convex mirror and in case of convex mirror,it is termed virtual focus as the rays of light donot actually pass through this point.

Focal Length:

The distance between the pole and principal focus of a  spherical mirror is called The Focal Length of that mirror.

It is denoted by  f  

f = R/2

Where R represents The Radius Of Curvature.

Linear Magnification:

The ratio of height of image to height of an object is called as Linear Magnification and is denoted by m

Magnification = m= Image Height/Object Height.

Uses Of Spherical Mirrors:

1.In huge shopping malls,convex mirrors are used for security purposes as they give a large field of vision.

2.Concave mirrors with parabolic shape are used in search light to throw an intense beam of light to a large distance.

3.Concave Mirrors are used for shaving as it gives an enlarged image of the face when someone stand between the principal focus and pole of the mirror.

4.Giant concave mirrors are also used in telescopes.

5.Convex mirrors are used in motorcycles and automobiles that enable the driver to see automobiles coming behind them.

6.Concave mirrors are used in medical equipment such as by doctors to examine ear,nose and throat of patients andin microscopes to view slides clearly.

Effect on image of object's position relative to mirror focal point (convex)

Object's position (S), focal point (F)	Image	Diagram
	Virtual Upright Reduced (diminished/smaller)

Object's position (S), focal point (F)	Image
(Object between focal point and mirror)	Virtual Upright Magnified (larger)

(Object at focal point)	Reflected rays are parallel and never meet, so no image is formed. In the limit where S approaches F, the image distance approaches infinity, and the image can be either real or virtual and either upright or inverted depending on whether S approaches F from above or below.

(Object between focus and centre of curvature)	Real image Inverted (vertically) Magnified (larger)

(Object at centre of curvature)	Real image Inverted (vertically) Same size Image formed at centre of curvature

(Object beyond centre of curvature)	Real image Inverted (vertically) Reduced (diminished/smaller) As the distance of the object increases, the image asymptotically approaches the focal point In the limit where S approaches infinity, the image size approaches zero as the image approaches F