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Chapter – 16 Light
Light: The natural agent that stimulates sight and makesthings visible. Lightis reflected from allsurfaces. It isa form ofenergy. Objects that give out light on their own are called luminous objects. Objects that do not give out light on their own are called non-luminous objects. They just reflect light that falls on them.When light reflected from an object enters into oureyes, the object becomes visible to us.
Reflection ofLight: Bouncing backof light after striking a shiny or polished surface, in the same medium, is called reflection.
Types of Reflection:
(i) Regular Reflection: When a beam of parallel light rays is incident on a smooth and plane surface, the reflected rayswill also beparallel. This typeof reflection iscalled Regular
Reflection. The reflection from a planemirror is anexample of regular reflection.
(ii) Diffused orIrregular Reflection: When light is incident upon a roughor uneven surface, it is reflected in many directions due to presence of irregularities on that surface. If a reflected light ray is reflected again on being incident on another surface, it is termed multiple reflections. Multiple reflections are used in periscopes. Periscopes are used in submarines, wartanks and by soldiers in bunkers to see objects that are notvisible directly. In a kaleidoscope, beautiful patterns areformed due to multiple reflections.
Laws ofreflection The angle ofincidence is equal to the angleof reflection. Incident ray,reflected ray andthe normal drawn at the pointof incidence tothe reflecting surface, lie in thesame plane.
Lateral inversion is the effect produced by a planemirror in reversing images from leftto right. Fore.g. our lefthand will appear as right andvice versa.
The imageformed by a plane mirror is: of the samesize as thatof the object left-right inverted erect and virtual formed behind the mirror at the samedistance as thedistance of theobject in frontof the mirror. Two mirrors inclined to each other give multiple images. Sunlight, called white light, consists of seven colours. Splitting of light into its constituent colours is known as dispersion. A normal eye can seenearby and distant objects clearly. Visually challenged persons can readand write using Braille system. Visually challenged persons develop their other senses moresharply to improve their interaction withtheir environment.
Parts of Human Eye: (i) Cornea: Transparent bulgeon the frontsurface of theeyeball which protects the eye andhelps in refraction of light. (ii) Iris: Coloured diaphragm behind the cornea which controls theamount of light entering the eye. (iii) Pupil: Dark hole inthe middle ofiris through which light enters theeye. (iv) Eye lens: Transparent, crystalline structure behind pupil and iris. (v) Ciliary muscles: Holethe eye lensin position andcontrol the focallength of theeye lens. (vi) Retina: Surface ofthe rear partof the eyeball where the lightentering the eyeis focused. (vii) Rods andCones:Rod cells respond to the brightness of light whilecone cells respond to colours. (viii) Blind spot: It isthe least sensitive point where norods and cones are present. (ix) The space between the cornea andthe eye lensis filled withaqueous humour. (x) The space between the eye lensand the retina is filled withvitreous humour.
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