# CHAPTER 15- NATURE OF LIGHT AND ELECTROMAGNETIC SPECTRUM

by • 29/07/2011 • Matric PhysicsComments (0)751

Newton‘s Corpuscular Theory of Light

This theory which was proposed by Newton is as follows:

• Light is emitted from a luminous body in the form of tiny particles called corpuscles.
• The corpuscles travel with the velocity of light.
• When corpuscles strike the retina they make it sense light.
• Medium is necessary for the propagation of light.
• Velocity of light is greater in denser medium.

## Wave Theory of Light

In 1676, Huygens proposed this theory. According to this theory:

• Light propagates in space in the form of waves.
• It can travel in space as well as in a medium.
• Light does not travel in a straight line but in sine wave form.
• Velocity of light is greater in rarer medium.
• Medium is not necessary for propagation.

## Quantum Theory of Light

According to this theory of Max Plank:

• Light is emitted from a source discontinuously in the form of bundles of energy called Photons or Quantum.
• It travels in space as well as a medium.
• Speed of light is greatest in space or vacuum.

## How A Rainbow is Formed?

As we know a prism disperses sunlight into a series of seven colors. When rain falls, raindrops behave like a prism and white light entering the raindrop splits up into seven colors on refraction. These are appeared as Rainbow.

## Spectrum:

After the dispersion of light or any electromagnetic wave, a band of colors is formed, which is known as a spectrum.

## Electromagnetic Spectrum:

Electromagnetic spectrum is a result obtained when electromagnetic radiation is resolved into its constituent wavelength.

## Waves of Electromagnetic Spectrum

It has a large range of wavelengths from a few millimeters to several meters.
Microwaves:

These radio waves have shorter wavelength between 1mm and 300 mm. Microwaves are used in radars and ovens.
Infrared Waves:

It has a long range. Its mean wavelength is 10 micrometers.
Visible Waves:

It has a range of 400 nm to 700 nm.
Ultraviolet Waves:

Their wavelength ranges from 380nm onwards. These are emitted by hotter start (about 25000 C).

## 1. Dual Nature of Light:

Light has dual nature, it behaves not only as a particle (photon) but also as a wave. This is called dual nature of light.

## 2. Dispersion of Light:

When a beam of sunlight falls on a prism, the light is split up in seven colors. This phenomenon is called Dispersion of Light.

## 3. Rainbow:

The rainbow is an arc of spectral colors formed across the sky during or after rainfall in the morning or when the sun is behind us.

## 4. Photons (Quantum):

Photons are tiny packets of energy. They behave as particles but actually they are not particles.