A mirror is an object that reflects light in such a way that you can see your image in it whether real or virtual, erect or inverted and diminished or enlarged. Plane mirrors are the common mirrors used in our home. This is different from other light-reflecting objects that does not preserve much of the original wave signal other than colour and diffuse reflected light.
There are two types of mirror they are:
A plane mirror is a mirror with a flat refractive surface. We use the plane mirror as a looking glass. Plane mirrors are the only type of mirrors for which a real object always produces an image that is virtual, erect and of the same size as the object.
A mirror whose polished, reflecting surface is a part of a hollow sphere of glass, is called a spherical mirror. One side of it is made opaque and another side acts as a reflecting surface.
Depending on the nature of the reflecting surface of the mirror, the mirrors are of two types:
A mirror which is a part of the sphere and is polished from the outer surface such as its reflecting side is inward is called a concave mirror. In this mirror, parallel rays of light converge at a point after reflection. A concave mirror is used to convert solar energy into heat energy, in torches and car's headlights to reflect the light of the bulb to form a powerful beam of light, in an astronomical telescope to view stars and planets.
Uses of Concave mirror
A mirror which is a part of the sphere and is silver polished from the inner surface such as its reflecting side is outward is called a convex mirror. In this mirror, parallel rays of light diverge after reflection. An image formed in the convex mirror is always virtual, erect and diminished. The convex mirror is used as rear view mirrors in cars, motorcycle, scooters, trucks, etc.
Uses of Convex mirror
Differences between Concave and Convex mirror
|Concave mirror||Convex mirror|
|A spherical mirror whose inner hollow surface is the reflecting surface is called a concave mirror.||A spherical mirror whose outer bulging surface is the reflecting surface is called a convex mirror.|
|It may give magnified or diminished image.||It forms diminished image (smaller in size only).|
|The image formed is real except when the object is between focus and principal.||The image formed is always virtual.|
Terms used in spherical mirror:
1. Pole: It is a geometrical centre of the surface of a mirror. It is represented by a point P.
2. Center of Curvature: It is the centre of the hollow sphere of which mirror is a part, represented by C.
3. The radius of Curvature: It is the radius of the hollow sphere of which mirror is a part, denoted by R.
4. Principal axis: The line joining the pole of the mirror and the centre of curvature and produced on both sides is called the principal axis.
5. Principal focus: The point on the principal axis where a beam of light incident to spherical mirror parallel to the principal axis converges or appears to be diverging from after reflection, is called the principal focus. It is denoted by the letter F. The principal focus is real in the concave mirror and virtual in the case of a convex mirror.
6. Focal length: It is the distance between principal focus and pole of the mirror. It is denoted by f. The focal length is half of the radius of curvature.
Ray diagram for Concave Mirror
Ray diagram for Convex Mirror
Sign convention for spherical mirrors
What is a spherical mirror?
A mirror whose polished, reflecting surface is a part of a hollow sphere of glass is called a spherical mirror.
What is a convex mirror?
A spherical mirror whose outer surface is reflecting surface is called a convex mirror.
What is a concave mirror?
A spherical mirror whose inner surface is reflecting surface is called a convex mirror.
Why is concave mirror also called a converging mirror?
A concave mirror is also called converging mirror because a parallel beam of light incident on it, converges to a point after reflection.
Why is convex mirror also called a diverging mirror?
Convex mirror is also called a diverging mirror because a parallel beam of light incident on it, appears to be diverging from a point after reflection.
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