Light, Shadows and Reflections: science class six
Shadows and its formation
The dark area where the light coming from a source is blocked by an opaque object is called a shadow.
In other words, a shadow is a dark area formed because of obscuring of the rays of light coming from a source by an opaque object.
How shadow is formed?
An opaque object does not allow light to pass through it. And when light is coming from a source and an opaque object is placed in its path then the opaque object blocked the rays of light passing through it. In such a situation we see the dark area on the screen or on the ground where light is obscured, this is the shadow.
Things required for the formation of shadows
Three things are necessary to form a shadow. These are light, an opaque object, and a screen. In the absence of anyone, the shadow is not formed.
Activity to cast a shadow
Some opaque objects, some transparent objects, a source of light, a screen
Take some opaque objects, some transparent objects, a source of light, and a screen.
You can consider the Sun as the source of light in the day time and consider the ground or a wall as a screen. But it will be better to perform this activity at the night. And it will be better to perform this with the help of one of your friends.
* Take a torch and some opaque objects, such as cardboard, a wooden or cardboard box, your geometry box, a ball, etc.
* Tell someone to hold the box in his hand and stand holding the box towards the wall.
* Now, throw the light of the torch to the box from a distance from the opposite side of the wall.
You will see the shadow of a box on the wall.
* Now take a different object like a ball and repeat the process.
You will see the shadow of the ball on the wall.
* Now, tell your friend to move the box or ball towards the wall and away from the wall in the direction of the torch.
You will see that when your friend moves the box or ball away from the wall the side of the shadow increases and when he moves the ball or box toward the wall the size of the shadow decreases.
Repeat the process with a translucent object, such as tinted glass or tracing paper.
In this case, you will observe that either no shadow is formed or an unclear shadow is formed.
Properties of Shadow
(a) The shape of the shadow depends upon the shape of the objects and the position of the source of light.
(b) Shadows give us some information about the shapes of objects.
(c) Sometimes, shadows can also mislead us about the shape of the objects.
(d) Size of the shadow depends upon the distance of the source of light from the object and the distance of the screen from the object.
The size of the shadow increases with the increase in the distance of the source of light and the distance of the screen from the object.
And the size of the shadow decreases with the decreasing of the distance of the source of light and the distance of the screen from the object.
(e) The colour of the shadow is always black in colour.
Observe You Own Shadow
On a sunny day, you must have observed your own shadow on roads or in the playground.
You will see that the length of your shadow will be longer at 10 am in the morning and at 3.00 pm in the evening.
You see that your shadow is shorter in the afternoon, i.e. at about 12.00 noon.
Shadows in Nature
Shadows of objects around us
On a sunny day, we can see the shadow of buildings, electric poles, trees, etc. which are formed because of the hindrance of sunlight passing through them.
When you will go under a tree in the afternoon, you will see many small shadows of leaves under the tree.
Solar Eclipse
The condition in which the visibility of the Sun gets hindered for some time in the day time because of the formation of the shadow of the Moon on the earth is called a Solar Eclipse.
Moon is an opaque object so it casts a shadow.
When the Sun, the Moon, and the Earth come in a straight line with the Moon in the middle the shadow of the Moon is formed on a particular area of the earth. In that condition the people leaving in that area do not see the Sun for some time, that is till the position of the Moon is in the middle. And when gradually the Moon moves from the middle between the earth and the Sun the Solar Eclipse becomes clear.
A Solar Eclipse takes place in the following condition
(a) When the Sun, the Moon, and the Earth come in a straight line with the Moon in the middle.
(b) On a new Moon day.
(c) The Solar Eclipse is visible only in those areas of the earth on which the shadow is formed.
Lunar Eclispe
The condition in which the visibility of the Moon gets hindered for some time in the night because of the formation of the shadow of the Earth on the Moon is called a Lunar Eclipse.
We know that we see the Moon because of the light coming from the Sun to it. Thus when the Earth comes between the Sun and the Moon in a straight line the shadow of the Earth falls on the Moon resulting stop the visibility of the Moon till the Earth does not move from this position.
The Lunar Eclipse takes place on the night of the Full Moon.
A Lunar Eclipse happens in the following condition
(a) When the Sun, the Moon, and the Earth come in a straight line with the Earth in the middle.
(b) On a Full Moon night.
(c) The Lunar Eclipse is visible only in those areas of the earth in which the shadow is formed.
Shadow of the Cloud
In the rainy season, the shadow of clouds can be seen often.
Sometimes we notice in the rainy season days that the clouds or a piece of cloud obscure the view of the sun and you feel some sort of shade on the hot and humid sunny days.
light of the sun gets dimmed for one minute, two minute, or for hours. This happens because of the overlapping of the view of the sun by clouds or a piece of cloud.
Sometimes you can have fun while chasing the moving shadow of clouds.
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