Light is a form of energy, which induces the sensation of vision in our eyes and makes us able to see various things present in our surrounding. The light ray may be objects self-light or reflected light.
Luminous objects are objects which emit light of their own.
Example: Sun, bulb, tubelight
Non-luminous objects are objects which reflect light from other sources. They do not emit light of their own.
Example: Moon, tree, table, painting.
Fig: Reflection of Light on mirror
TYPES OF REFLECTION
Light undergoes either diffuse or regular reflection.
(1) In regular reflection, a parallel beam of incident light is reflected as a parallel beam in one direction.
(2) Regular reflection of light occurs from smooth surfaces like that of a plain mirror.
(3) Images are formed by regular reflection of light.
(1) In Diffuse reflection, a parallel beam of incident light is reflected in different directions.
(2) The diffuse reflection of light takes place from rough surfaces.
(3) A sheet of paper produces diffuse reflection of light. No image is formed in diffuse reflection of light.
Fig: Diffused reflection
Characteristics of image formed by a plane mirror:
(1) The image formed by a plane mirror is virtual & Erect.
(2) The image formed in a plane mirror is the same distance behind the mirror as the object is in front of it.
(3) The image formed in a plane mirror is of the same size as the object.
(4)The image in a plane mirror is laterally inverted.
Fig: Plane Mirror Reflection Image
Uses of plane mirror:
1. To see ourselves
2. To make some instruments like periscope
3. In shops for decoration
(i) When two or more mirrors are placed at an angle to one another, we can see multiple images of an object.
(ii) For example in the hair dresser shop two mirrors are placed opposite to each other. If a man is sit between them, His image is formed in both the mirrors. The image in one mirror would act as an object for another mirror and this sequence would continue. This will give result in the formation of multiple images.
(iii) If two plane mirrors are inclined at an angle q, then the number of images formed in them is given by the formula:
No. of images formed = (3600/ q) - 1
(iv) If the given two mirrors are at a right angle to each other, 3 images will be obtained. If the given mirrors are at 60° angle, we shall get 5 images.
(v) When the two mirrors are kept opposite and parallel to each other, we will get infinite number of images formed.
Kaleidoscope: The kaleidoscope is an instrument which produce multiple reflections of colored glass pieces (or colored plastic pieces) and create beautiful patterns.
Fig: Kaleidoscope changing pattern of colorful images
Construction: The Kaleidoscope consists of three long and narrow strips of plane mirrors inclined at 600 to one another forming a hollow prism, and fitted into a cardboard tube. One end of the cardboard tube is closed by an opaque disc (cardboard disc) having a small hole at its centre. The other end of cardboard tube is closed with circular discs of glass. The inner disc being of transparent glass (clear glass) and the outer disc of ground glass (translucent glass). A number of small pieces of different colored glass (or plastic) and having different shapes are kept between the two glass discs (which can move around freely in the space between the two glass discs). When we hold the kaleidoscope tube towards light and look inside it through the small hole, we see beautiful patterns of colored glass.
Fig. Patterns formed by Kaleidoscope
DISPERSION OF LIGHT
The splitting up of white light into seven colors on passing through a transparent medium like a glass prism is called dispersion of light. The seven colors of the spectrum of white light are: violet, indigo, blue, green, yellow, orange and Red.
Fig: Dispersion of light
The Human Eye
Fig: The Human EyeRods and cones
Fig: Myopia and Hypermetropia the Defects of the Eye