LIGHT AND SHADOWS
During the day hours we can see everything clearly. But in the night we have to switch on the light. Switch off the lights of the room in night! Are you able to see anything? The answer is known, it is no. We have understood that only through light the things can be seen. Light is a form of energy that makes everything visible around us. Let’s know about it in more detail.
SOURCES OF LIGHT
A source of light can be defined as the point from where the light originates. There are two types of light sources: natural and artificial.
Natural Sources: The sources of light that exist in the nature are called natural sources. For example, Sun and moon. During the day the Earth is enlightened by the light of the Sun and in the night moon shines in the sky.
Artificial Sources: The sources of light which are created by men to emit light are called artificial sources. For example, bulb, tubelight, etc. They don’t exist naturally they are made by men so that they can be used as source of energy.
LIGHT TRAVELS IN A STRAIGHT LINE
The light always travels line straight line. The speed of light in air is 3 x 108 m/s. Some of the following examples will illustrate the same.
- In a dark room if a pinhole is made and light source is kept at the hole, we’ll notice that the beam of light travels in a straight line and does not disperse in the whole room.
- The headlight of the car or bike in a foggy or misty night can be seen travelling in a straight line.
- The shadows are formed because light travels in a straight line.
- The Sunlight reaches us on the Earth because light travels in a straight line. As between the Sun and the Earth there is only vacuum, if the light does not travel in straight line, it cannot reach the surface of Earth.
All the above examples give a clear view that light travels in a straight light. The property of light travelling in a straight line is called rectilinear propagation of light.
HOW DO WE SEE?
We see so many things around us trees, wall, chair and table. Not all the things emit light then how do we see them? Well, our eyes play a very important role in this.
When the light from a source falls on a surface, it is reflected back to our eyes. The image of the object is formed in our eyes as it is formed in camera when a picture is clicked. Thus, we are able to see the objects around us.
Depending upon which objects have their own light and which reflect back, the objects are classified into two types:
- Luminous objects: These are those sources which generate their own light. For example, Sun, bulbs and tubelights.
- Non-luminous objects: The objects which do not have their own light but they reflect the light falling on them are called non-luminous objects. For example, moon, wood and table.
When the light falls on a surface it gets reflected. The amount of light that gets reflected depends upon the kind of surface. If the surface is smooth, the whole light falling on it gets reflected. If the surface is rough, most of the part of the light is absorbed and only a few is reflected back.
Depending on how much light can pass through surfaces, there are three types of objects.
- Opaque: These objects don’t allow light to pass through them at all. For example, wood, chair, table, and wall.
- Translucent: The objects which allow only a little amount of light to pass through them are called translucent. For example, butter paper.
- Transparent: The objects which allow the light to pass through them completely are called transparent. For example, glass and clear plastics.
The shadows are created by the blockage of the light by an opaque object. The shadows do not remain the same everytime. The shadow is affected by the size of the source of light, the intensity of light, the direction of light and the distance between source and object.
- If the source of the light is increased, the size of the shadow also increases.
- The brighter the source, the darker is the shadow.
- The shadow is always formed in the direction opposite to the direction of the source of light.
- If the distance between the source and the object decreases, the size of the shadow increases.