Light and our Sight, Shadows
We cannot see things in a dark room. However, as soon as we switch on a lamp, we can see the lamp immediately because its light reaches our eyes. At the same time, the light given off by the lamp falls on other objects in the room. These objects reflect the light to our eyes. Therefore, we can see them too. When we are outdoors in the day, we can see things around us. Again, this is because they reflect sunlight to our eyes.
From the above discussion, we can see that our sense of sight relies on both the presence of light sources and the reflection of light. As long as a light source is present, other objects can reflect the light given off by the light source to our eyes. We are able to use our sense of sight to see things around us.
We have learnt that opaque objects do not allow light to pass through them. Also, when light falls on an opaque object, it cannot bend and go round the object because light travels in straight lines. Thus, there is an area behind the object where light does not reach. This means that no light is reflected from this area to our eyes. Thus we see an area of darkness behind the object. This is what we say that the object casts a shadow.
A shadow is an area of darkness that is formed on a surface when an object stands between a light source and the surface. The shadow is formed as light is blocked by the object. The shape of a shadow resembles the outline of the object that casts the shadow. For example, when you shine a torchlight onto a monkey sitting in front of the wall, a shadow of the monkey appears on the wall. This shadow resembles the shape of the monkey.
The same object can cast shadows of different sizes. When the object is placed nearer to the light source, it casts a bigger shadow. An object can cast shadows of different shapes. When we look at the same object from different angles, the outline of the object appears to be different. Similarly, when different parts of the same object block the light, the object can cast shadows of different shapes.
A small lamp (or a larger one placed further away) will throw sharp shadows. A large source of light such as one coming from a fluorescent tube gives much lighter shadows with very blurred edges. In summary, shadows are formed when an object blocks light from passing through (transmitting). The size of the shadow depends on the position of the object, position of the light source and the screen the shadow falls on.
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