In this blog, we will learn about the Difference Between Image and Shadow and Factor affecting the Shape of a Shadow. Let's start with light first because a shadow can't be formed without light.
Light travels in a straight line: You must have seen shadows of trees, buildings, vehicles, and many other objects. Shadow is an area where direct light from a luminous object or light source cannot reach due to obstruction by an opaque object. When an object blocks light, it forms a shadow. Let us do an activity to understand how light moves
- Take a piece of flexible PVC pipe.
- Light a candle and fix it on a stand
- Now place the candle stand on a table at one end of a room
- Standing at a distance from the table look at the candle through the P.V.C. pipe.
- Adjust your position so that you are able to see the flame of the candle through the pipe.
- While holding the pipe with one hand, bend the pipe a little with your other hand. What do you find?
- Now the flame of the candle is not visible.
You cannot see the candle through the pipe even if you turn the bent pipe a little to your right or left.
We conclude from this, that light travels along a straight line. That is why when an opaque object obstructs light a shadow is formed.
Difference between a Shadow and an Image: Let us understand the major difference between a shadow and an image.
| Shadow | Image |
| 1. Shadow is formed by obstruction of light | 1. Image is a true reflection of an object |
| 2. Shadow is a region of the absence of light | 2. Image is formed by light rays. |
| 3. Shadow provides only a rough outline of an object as the shadow is only a dark patch formed on a surface. | 3. Image of an object provides all the details of the object like shape and colors. |
| 4. Shadow can be seen only on the surface | 4. Image formed by a plane mirror cannot be seen on a screen. |
| 5. Size of the shadow can be changed by changing the position of the object & source of light. | 5. Size of image in a plane mirror is always the same as that of the object. |
Factors affecting shape of a shadow
We have learned about the formation of a shadow. To make a shadow three things are needed. The first thing is the source of light, the second is an opaque body and the third is a screen. We cannot get a shadow if any one of these three is absent. When light rays are blocked by an object. Shadow is formed. Shadow can be seen on a screen. Wall of a room, side of a building, the ground act as a screen. Shadow and light sources are always on the opposites sides of the opaque body when the sun is in front of you, your shadow forms behind you.
The size and shape of a shadow depend on the orientation of the object with respect to the rays of light.
In other words, we can say the size of a shadow depends upon the quantity of light blocked. It is observed that the length of a shadow is maximum when the sun is at a low altitude or near the horizon during morning and evening.
When the sun is overhead during noon, the light blocked is minimum therefore the shadow is shortest.
- Size of the body: - A small tree makes a small shadow. A big building makes a big shadow. When the earth blocks the sun�s light from reaching the sky above, the whole sky above us appears dark.
- The relative position of the light source and the object:- Make shadow of a ball on the wall of a dimly lit room, using torch as a source of light. Change the distance between the ball and the torch either by moving the ball or by moving the torch. What do you observe?
- We find the size of the shadow increases when the distance between the ball and the torch decreases. Keeping the distance between the ball and the torch fixed move the set up of the ball and the torch. What do you observe? As the ball and the torch set-up moves away from the wall the size of the shadow increases.
- Solar and Lunar Eclipse: - We see a solar eclipse when the shadow of the moon falls on the earth.
- Lunar eclipse occurs when the shadow of the earth fall on the moon.
Read More- Luminous and Non Luminous Objects- Science Class 6
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