7.4 Shadow formation
Light travels in a straight line. When an obscure object is placed in the path of light it cannot pass through it.Instead it forms a shadow.
Shadow is a dark region behind an obscure object. The location, size and shape of the shadow depend upon the location and distance of a light source.
If we move the light source, the shadow of object also moves. This is because the light rays keep changing their direction in which they fall on the object.
If the object moves, then again the shadow moves as it is formed when the object blocks light.
1. Location of light source
The shadow appears to be larger when light rays fall on them diagonally. When light rays fall on the objects vertically, the shadows appear to be small, For instance, Sun rays fall on the objects diagonally in the morning.
The shadows formed appear to be larger. Shadows appear to be smaller in the noon as light rays fall on the object vertically.
ii. Distance from a light source
The size of the shadow also depends on the distance of an object from the light source. The shadow of an object is bigger if object is close to the source of light. Shadow of an object is smaller as object moves away from the source of light.
Shadow disappears in cloudy weather due to less sunlight whereas in a bright sunny day shadow becomes clear.
7.5 Eclipse
Eclipse is a shadow that is formed in space. We know that Earth is revolving around the Sun and Moon is revolving around the Earth.
During their motion the Sun, Moon and Earth come in the straight line. In this situation the Earth and Moon make shadows on each other.
These shadows of the Moon and Earth are called Eclipses. Eclipses are of two types.
- Solar Eclipse
- Lunar Eclipse
i. Solar Eclipse
When the Moon moves between the Sun and the Earth,it has an eclipse.For a short period of time, Moon blocks the light coming from the Sun to Earth.
It causes darkness on the parts of the Earth. When a complete solar eclipse occurs, day turns into night. This temporary darkness is known as umbra shadow.
ii. Lunar eclipse
In this situation, Earth blocks the light coming from the Sun to reach the Moon. In this way, the shadow of Earth is formed on the Moon and Moon looks dark.
The condition is called eclipse. The complete lunar eclipse is known as Penumbra Lunar partial eclipse is known as penumbra lunar eclipse.
You can also understand solar and Lunar eclipses by performing the following activity.
7.6 Pinhole camera
A pinhole camera works on the scientific principle that light always travels in a straight line. A pinhole camera is a small box with a black inner walls and a tiny hole in the centre of one end. Light cannot enter in it.
The only entrance of light is a small, tiny hole at one surface. It is called pinhole camera due to this hole. Its inner walls are kept black to avoid reflection of light. The Light of an object can passes through a pinhole. It goes to the screen where it forms inverted and small image.
The colour of the image is the same as the objects.if the pinhole is small,the image will be sharp and clear. If the pinhole is large, many images will be formed on the screen or blurred image will be formed.
The most common use of a pinhole camera is to capture the sun's movements over a long period of time. Such photography is called Solar-graphy. Similarly, pinhole camera is also used to observe the Sun directly.
