Optics

Light is a form of energy with which we see things around us. Light is only a small part of the vast spectrum of electromagnetic radiation.

Optics deals with the study of properties of visible light. Visible light has seven different colors viz. violet, indigo, blue, green, yellow, orange and red. A combination of these colors gives rise to white light. The characteristic that distinguishes these colors is the wavelength, with violet having a wavelength of nearly 400 nm and red having the highest wavelength of nearly 650 nm. A source of light may be considered as emitting energy either as a stream of particles called photons or as wave motion in space. This dual nature of light makes it unique in many ways.

Reflection of light:

When light is incident on a surface it partly goes back, partly absorbed by the surface and the remaining part if any, is transmitted through the surface. The part which partly goes back is called reflected light.

Laws of Reflection:

• The incident ray, the normal at the point of incidence and the reflected ray all lie in the same plane.
• The angle of incidence is always equal to angle of reflection.

Refraction of Light:

The phenomenon of change in path of light as it goes from one medium to another is called refraction.

Laws of Refraction:

The phenomenon of refraction takes place according to following two laws:

• The incident ray, the normal to refracting surface at the point of incidence and the refracted ray- all lie in the same plane.
• The ratio of the sine of angle of incidence to the sine of angle of refraction is constant for the two given media. This constant is also called relative refractive index of medium. This law is also called Snell's law of refraction.

Interference of Light:

The phenomenon of non-uniform distribution of energy in the medium due to superposition of two light waves is called interference of light.

Diffraction of light:

The phenomenon of bending if light round sharp corners and spreading into the regions of the geometrical shadow is called diffraction.

Diffraction of light is of two types:

• Fresnel diffraction: It is a type of diffraction that takes place at a slit, when the source of light lies at a finite distance from it.
• Fraunhofer diffraction: it is a type of diffraction that takes place from a slit, when a plane wave front is incident on it and wave front emerging from the slit is also plane.

Polarization of light:

The phenomenon due to which vibration of light are restricted in a particular plane is called polarization of light.