Question

Show the reflection of light by a plane mirror. man and the and the shadow
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Answer 1

Light, Shadows and Reflections

1. INTRODUCTION

If we enter a dark room, objects present there are not visible. However, if a bulb is switched on, everything in the room becomes visible. It shows that for vision the presence of light is essential.

Definition of Light: It is an invisible energy which causes in us sensation of sight (vision). Since light is obtained from heat energy, i.e., when an object is heated to a temperature beyond [500 0C, we can say that light is a kind of energy].

It must be kept in mind that light energy makes the surrounding objects visible, but by itself it is an invisible energy.

Example: If we are seeing a coloured poster, then we are seeing only the poster and not the  coloured lights reflected fronts it. It is because light is invisible. The various colours reflected from the poster excite the retina of the eye, which in turn sends a message to the brain. It is the brain which finally makes out the colours of the poster. Thus, we can conclude that light is an invisible energy which causes in us sensation of vision.

Sources of Light: Sun is the primary source of light for mankind. In addition to it, lighted bulb, a fluorescent tube, a lighted candle ,a kerosene oil lamp, etc., are other sources of light.

Speed of Light: Light travels at very fast speed i.e., 3×108" role="presentation" style="margin: 0px; padding: 0px; box-sizing: inherit; border: 0px; font-size: 15px; font-style: normal; font-weight: normal; outline: 0px; vertical-align: baseline; display: inline; line-height: normal; text-indent: 0px; text-align: left; text-transform: none; letter-spacing: normal; word-spacing: normal; overflow-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; position: relative;">3×1083×108 m/s. It means the speed of light is 300000000 m/s or 300000 km/s.

Luminous Bodies: The bodies which give out light energy by themselves are called luminous bodies. Examples: The sun, the stars, glow worm etc.

Non-luminous Bodies: The bodies which do not give light energy by themselves , but reflect the light energy falling on them are called non-luminous bodies. Examples: moon, wood, furniture etc.