REFLECTION ON PLANE MIRROR

 

REFLECTION ON PLANE MIRROR

The process through which light rays fall on the surface and gets bounced back is known as reflection of light.

Concepts Of Reflection.

Non-luminous objects are seen when they reflect or throw back light from a luminous object like a candle flame or sun. when light falls on such surfaces, it is either absorbed, transmitted or reflected. Sometimes a combination of the above processes may occur.

There are two types of reflection

i.                      Regular Reflection: Parallel rays of light incident on a smooth or polished surface are reflected as parallel rays in one direction. E.g. mirror

ii.                     Diffused or Irregular Reflection: Parallel rays of light incident on a rough or irregular surface are reflected in various directions. E.g page of a book or surface of a cloth.

 Laws Of Reflection

I.                     The incident ray, the reflected ray and the normal at the point of incidence all lie in the same plane.

II.                    The angle of incidence (i) is equal to the angle of reflection (r ) .

 Terms Associated With Reflection Locating Image.

i.                      A virtual image is one that cannot be caught on a screen. It is one through which rays of light do not actually pass but which nevertheless visible to the eye.

ii.                     A real image is one that can be caught on a screen. Light rays actually pass through a real image.

Parallax is the apparent relative movements of two aligned objects when they are not at the same distance from an observer. Non- parallax occurs when both the object and its image move together in the same direction when an observer moves his eyes from side to side.

Parallel lateral inversion image produced on plane surface.

The effect of the plane mirror on objects placed in front of it whereby the appearance of the image looks like a reversal of the object is known as lateral inversion. Lateral inversion is due to the fact that an object is perpendicularly opposite its image behind the mirror.

Principle of reversibility: This principle states that the path of a light ray is reversible.

Properties of image produce of plane mirror.

I. It is the same size as the object.           II. It is virtual            III. It is laterally inverted.          IV. It is upright

V. It is as far behind the mirror as the object is in front of the mirror.

 Image produced on an inclined plane.

The number of images formed depends on the angle between the two mirrors according to the formula n =  - 1. Where n is the number of images,  is the angle between the two mirrors.

Example: How many images will form when the angles between the two mirrors is 60^o.

Solution: n =  – 1; n =  – 1= 6-1= 5 images.

 Image produce from parallel plane surfaces.

 When =0 i.e the two mirrors are placed parallel to each other, and an object is placed between them, the number of images formed is infinite. These images all lie in a straight line through the object, and perpendicular to the mirrors.

Effect of mirror rotation on a reflected ray.

If the direction of an incident on a mirror is kept constant and the mirror is rotated through an angle, it will be found that the reflected ray will be rotated through twice that that angle. This is an important fact which is made use of in mirror galvanometers used in measurement of very small electric currents, and in the navigator’s sextant

Application of plane minor

I.  in kaleidoscope    II. In periscope           III. In mirror galvanometer                    IV.  In navigator’s sextant.

Applications of reflection of Waves in Daily Life
Safety
i) The rear view mirror and side mirror in a car are used to view cars behind and at the side while overtaking another car, making a left or right turn and parking the car. The mirrors reflect light waves from other cars and objects into the driver's eyes.
ii) The lamps of a car emit light waves with minimum dispersion. The light bulb is placed at the focal point of the parabolic reflector of the car lamp so that the reflected light waves are parallel to the principal axis of the reflector. Parallel light waves have a further coverage.
Defence
i) A periscope is an optical instrument. It can be constructed using two plane mirrors for viewing objects beyond obstacles. The light waves from an object which is incident on a plane mirror in the periscope are reflected twice before entering the eyes of the observer.
Telecommunications
i) Infrared waves from the remote control of an electrical equipment (television or radio) are reflected by objects in the surroundings and received by the television set or radio.