These have curved reflecting surfaces and are also called curved mirrors. These mirrors are made from a hollow sphere. There are two types of curved surfaces at each hemisphere. The inner curved surface is termed as concave, while the outer is called convex. Spherical mirrors are different from plane mirrors due to their reflecting surface.
Types of Spherical Mirrors
There are two types of spherical mirrors.
- Concave mirror
- Convex mirror
If the reflecting surface of a mirror is concave, then it is called a concave mirror. A concave mirror is also known as a converging mirror. It is used to magnify objects. Concave mirrors are used by dentists to obtain a magnified image of the teeth. They are also used in solar heaters or solar concentrators, and as reflectors in flashlights, and headlights of cars and scooters.
- The image formed by a concave mirror when the object is placed close to it is virtual, erect and magnified.
- The image formed by a concave mirror when the object is moved away from it is real, inverted, and magnified.
- The image formed by a concave mirror when the object is placed far away from it is real, inverted and diminished.
If the reflecting surface of a mirror is convex, then it is called a convex mirror. A convex mirror is also known as a diverging mirror or fish eye mirror.
The image formed by a convex mirror is virtual, erect and diminished. It means that a larger area is visible in a convex mirror than in a plane mirror of the same size. That is why convex mirrors have a variety of applications – as reflectors at sharp turns and tricky or ‘blind’ corners and in parking lots, and as rear-view mirrors in cars and on motorcycles.
Rear-view mirrors enable the driver/rider to watch the road behind them. They are also used in super markets, stores and ATM centres as a security measure. Objects like thumb tacks, Christmas baubles and sunglasses act as convex mirrors.
The image formed by a plane mirror cannot be captured on a screen, and is called a virtual image.
Images that can be captured on a screen are known as real images. For example, in a camera, images are real and can be captured on the negative, which acts as a screen.
Opaque Spherical Surface
In an opaque spherical surface, the silvered surface acts as a mirror. So, a concave mirror will have its concave side silvered, while a convex mirror will have its convex side silvered.
Transparent Spherical Surface
For a transparent spherical surface, if the concave surface is silvered and later coated with red oxide, then the mirror acts as a convex mirror. Also, if the convex surface is silvered and later coated with red oxide, then it acts as a concave mirror.
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