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

Radio Waves:

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).

Definitions

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.

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