# Important Points and Formulas of class 7 Science Chapter-Light

## Class 7 Science Chapter-Light

It is a matter of common experience that the objects inside a dark room, which are invisible, become visible when the room is illuminated by a source of light. Thus, light can be defined as the external cause responsible for the sensation of vision.

The branch of Physics dealing with the nature and properties of light and vision is called optics

### Nature of Light - Theories

Light is a form of energy. Energy can be transferred from one point to another point either by particle motion or by wave motion. Accordingly different theories on the nature of light have been proposed.

The important theories are as follows:

1. Newton's Corpuscular Theory
2. Huygens' Wave Theory
3. Maxwell's Electromagnetic Theory
4. Planck's Quantum Theory

### Newton's Corpuscular Theory

About-Light According to Sir Issacs Newton's Corpuscular Theory, a luminous body continuously emits tiny, light and elastic particles called corpuscles in all directions. When these particles fall on the retina of the eye, they produce the sensation of vision.This theory could explain a number of phenomena concerning light like rectilinear propagation, reflection and refraction. Reflection was explained by assuming that the corpuscles which fall on a smooth surface would bounce back like rubber balls hitting a wall. When this theory was used to explain refraction, scientists found that the velocity of light in a denser medium would be more than that in a rarer medium. However, the experimental findings of Foucault pushed back the corpuscular theory of Newton. This corpuscular theory could not explain satisfactorily certain other phenomena.

### Huygen’s Wave Theory

In 1967 Christian Huygens proposed the wave theory of light. According to this, a luminous body is a source of disturbance in hypothetical medium called ether. The disturbance from the source is propagated in the form of waves through space and the energy is distributed equally in all directions. Even though this theory could satisfactorily explain several optical phenomena, the presence of ether could not be detected.

### Maxwell's Electromagnetic Theory

Electromagnetic theory of light was put forward by James Clerk Maxwell in 1873. According to this theory, light consists of fluctuating electric and magnetic fields propagating in the form of electromagnetic waves. But this theory failed to explain the photoelectric effect.

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Find Below Short Notes of chapter-Li​ght