Light Shadows and Reflections - Revision Notes
CBSE Class–VI Subject Science
Revision Notes
CHAPTER – 11
Light, Shadows and Reflections
Light: Light is the natural agent that stimulates sight and makes things visible.
- Its path is only visible when it is scattered by dust particles present in the atmosphere.
- Light is a form of invisible energy.
- Light itsel is not visible .
- It makes other objects visible.
- Light and the eyes both are necessary to see the things.
- The sensation which helps us to see things is called sight or the vision.
SOURCES OF LIGHT
- Sun,
- stars
- electric torch,
- candle flame
Light is classified into two:
(i) Emission of light: Classifying objects on the basis of emission of light.
LUMINOUS OBJECT :- objects which emit their own light are called luminous objcts.Ex. A candle, electric torch.
NON-LUMINOUS OBJCTS :- Objects which do not have their own light and are seen by the light scattered by them are called non-luminous objects.. Example: moon, chair, table, etc.
- Optical media :- Any substance which allows ligt to pass through it either partially or wholly is calle an otical media.·
- Transparent: All substances that allow light to pass freely through them and through which objects can clearly be seen are called transparent substances.Example: glass, water, air, etc.
- Translucent: A substance that allows light to ass through it only partially is calle a translucent medium or substance.. Example: butter paper, tissue paper, etc.
- Opaque: Objects that do not allow light to pass through them. Example: book, brick, etc.
Shadow: A shadow is the 'region of absence of light'. Light from a source is cut off by an obstacle and shadow is formed.
- Opaque object cast a dark shadow.
- Translucent objects produce a weak shadow.
- Transparent objects do not cast a shadow at all.
Types of shadow:
The kind of shadow depends upon the size of he source of light.
Due to smaller (point) light source: Only one dark shadow is formed and this is known as umbra.
Due to larger(extended) light source: Two shadows are formed-a dark one in the centre and a light one on the outside. Dark shadow is called umbra and the faint or lighter shadow is called penumbra.
- The size of umbra decreses and penumbra increses as the the screen is moved away from the object.
Colour of shadow :- Whatever be the colour of the opaque objcet , the shadow formed is always of the same colour , that is , black.
LENGTH OF THE SHADOW :- The length of the shadow differs depends upon the angle at which light falls on a body.
- Eclipse: A shadow formed in space that makes the sun or the moon invisible for some time.Eclips is the overshading of a bright obect.
- Solar eclipse: The moon comes between the sun and the earth, so that the earth (in the shadow) darkens during the day.
- The solar eclips occurs only on a 'NEW MOON DAY' .
- Lunar eclipse: The moon and the sun are in a straight line such that the earth is in the between the sun and the moon, the shadow of the earth falls on moon and the moon cannot be seen.
- The lunar eclips occurs on a 'FULL MOON ' NIGHT.
(ii) Reflection of light: The process of sending back the lig