Category :
8th Class
Light
Synopsis
- Light is a form of energy. It is an electromagnetic radiation which can travel through vacuum with a speed of \[3\times {{10}^{8}}\,\,m{{s}^{-1}}\]. Light travels along straight lines. This property is known as the rectilinear propagation of light. We can see an object only when it reflects or scatters the light falling on it.
- Any polished or shining surface acts as a mirror and regular reflection takes place.
- When there is no regular reflection, sharp images are not obtained and so they cannot be seen by us. This happens because of scattering of light due to irregular reflection.
- An image which can be obtained on a screen is called a real image.
- An image which cannot be obtained on a screen is called a virtual image.
- The image formed by a plane mirror is erect. It is virtual and is of the same size as the object. The image is at the same distance behind the mirror as the object is in front of it. In an image formed by a plane mirror, the left side of the object is seen on the right side in the image, and right side of the object appears to be on the left side in the image. This is known as lateral inversion.
- If two plane mirrors are placed at an angle between them, a number of images are formed. If the angle between the mirrors is 6, then the number of images formed "n" is given by the formula,
\[n=\left[ \frac{360}{\theta }-1 \right],if\,\frac{360}{\theta }\] is even and \[n=\frac{360}{\theta },\]if it is odd.
- White light is composed of seven colours.
- The splitting of light into seven colours is known as dispersion of light. Rainbow is a natural phenomenon showing dispersion.
- Human eye consists of structures like cornea, iris and pupil.
- Visually challenged persons (blind) can read and write using the Braille code.
