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CBSE Class–VI Subject Science Revision Notes CHAPTER – 11 Light, Shadows and Reflections Light: Light is the natural agent that stimulates sight and makesthings visible. Its pathis only visible when it isscattered by dustparticles present inthe atmosphere. Light is a formof invisible energy. Light itsel is not visible . It makesother objects visible. Light andthe eyes bothare necessary tosee the things. The sensation which helps usto see things is called sight or the vision. SOURCES OFLIGHT Sun, stars electric torch, candle flame Light isclassified into two: (i) Emission of light: Classifying objects on thebasis of emission of light. LUMINOUS OBJECT :- objects which emittheir own light are called luminous objcts.Ex. A candle, electric torch. NON-LUMINOUS OBJCTS :- Objects whichdo not havetheir own lightand are seenby the light scattered by them arecalled non-luminous objects.. Example: moon, chair, table, etc. Optical media :- Anysubstance which allows ligt to passthrough it either partially or wholly is calle anotical media.· Transparent: All substances that allow light to pass freely through them andthrough
which objects can clearly beseen are called transparent substances.Example: glass, water, air, etc. Translucent: A substance thatallows light toass through itonly partially iscalle a translucent medium or substance.. Example: butter paper, tissue paper, etc. Opaque: Objects thatdo not allowlight to passthrough them. Example: book, brick, etc. Shadow: A shadow isthe 'region ofabsence of light'. Light from asource is cutoff by an obstacle andshadow is formed. Opaque object cast a dark shadow. Translucent objects produce a weak shadow. Transparent objects donot cast ashadow at all. Types ofshadow: The kindof shadow depends upon the sizeof he source of light. Due tosmaller (point) lightsource: Only onedark shadow is formed andthis is knownas umbra. Due to larger(extended) light source: Two shadows are formed-a dark one in the centre anda light oneon the outside. Dark shadow iscalled umbraand the faint or lighter shadow is called penumbra. The size ofumbra decreses andpenumbra increses asthe the screen is moved away from theobject. Colour ofshadow :- Whatever bethe colour ofthe opaque objcet , the shadow formed is always ofthe same colour , that is , black. LENGTH OF THE SHADOW :- The length of the shadow differs depends uponthe angle at which lightfalls on a body. Eclipse: A shadow formed in spacethat makes thesun or themoon invisible forsome time.Eclips isthe overshading of a bright obect.
Solar eclipse: The mooncomes between thesun and theearth, so thatthe earth (inthe shadow) darkens during the day. The solar eclips occurs onlyon a 'NEWMOON DAY' . Lunar eclipse: The moon and thesun are ina straight linesuch that theearth is inthe between the sun and the moon, the shadow of the earth falls on moon and the moon cannot be seen. The lunar eclips occurs ona 'FULL MOON' NIGHT. (ii) Reflection oflight: The process of sending backthe light rayswhichafall on thesurface of an object. Silver metal is oneof the bestreflector of light.
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