Engineering Physics

by

BhaskarDepartment of Physics

K L University

Lecture 1 (23 July)Introduction to Optics

Interference

Basics of LightLight exhibits different properties such as

• Reflection• Refraction• Interference• Diffraction• Polarization

Its also shows two phenomenon : • Photoelectric effect• Compton Effect

Basics of Light…..

Theories:

Ray Theory Wave Theory Particle Theory

Ray theory of Light

Ray theory of Light• In many applications of interest the wavelength λ of light is

short compared with the relevant length scales of the optical components or system (e.g. mirrors, prisms, lenses).

• This branch of optics is referred to as Ray optics or Geometrical Optics, where energy of light is propagated along rays.

• The rays are perpendicular to the wave fronts.

Ray theory of Light…..Law of Ray optics :a) Light ray travels in a straight line in homogenous medium.

b) When there is change of medium in the propagation of light ray, there is reflection and refraction of light happens at the boundary of medium.

Ray theory of Light…..Law of Reflection:

Incident ray, reflected ray and normal of the incident surface must lie in one plane and the angle of reflection must be equal to angle of incident.

Ray theory of Light…..Law of Refraction:

Incident ray, refracted ray and normal of the incident surface must lie in one plane and the angle of incidence θ1 and the angle of refraction θ2 are related to each other, and to the refractive indices of the medium by Snell’s law of refraction.

Ray theory of Light…..Refractive index:

A number that describes how light, or any other radiation, propagates through that medium.

n = C/vFor any medium n≥1For Water, n = 1.33 Glass, n = 1.45~1.48

Critical Angle

Snell’s Law: when, n1>n2 ;

Total Internal Reflection

Light ray guiding condition

Wave theory of Light…..

What is wave…….?

Simply disturbance on the surface of a liquid body, as the sea or a lake, in the form of a moving ridge or swell.

• Wave theory for light was proposed by an DUTCH PHYSICIST named as CHRISTIAN HUYGENS, in 1678

Crest

Trough

Wave theory of Light…..

Parameters of Light:

Wave length(λ): The distance between two successive particles which in the same phase of vibration on the wave is known as wavelength.

Wave theory of Light…..

Parameters of Light:

Frequency: Number of vibrations per second completed by the particle on wave is called as frequency.

Time Period

Amplitude

Velocity

Intensity

Light is an electromagnetic radiation, in which electric and magnetic fields are perpendicular to each other and propagation of light is perpendicular to both electric and magnetic field.

Characteristics of Light:• Intensity• Wavelength (Color)• Polarization

Wave theory of Light…..

Interference: The superimposition to two waves one in to another is known as interference

Diffraction: The phenomenon exhibited by wave fronts that, passing the edge of an opaque body, are modulated, there by

causing a redistribution of energy within the wave front.

Polarization: Polarization is a property of waves that describes the orientation of oscillations.

Such as Linear, Circular, Elliptical, Random

Wave theory of Light…..

Particle theory of Light…..

But the wave theory doesn’t explains the phenomena's such as Photo electric effect and Compton effect.

Then particle theory introduced.

In 1900 Max Plank interfused that the light also travel as tiny bundles of energy called light quanta, or photons. The energy of each photon is directly proportional to its frequency.

For that Plank got Nobel prize and he also explained Photo electric effect based on this theory. It explained by particle theory, cause light is quantized.

Finally it’s conclude that the Light has dual nature. It has both particle nature and wave nature but it cannot act as a wave and particle simultaneously.

Phase Difference: The angular separation between two points of

wave is called Phase difference.It is measured in radians or degrees.

Path Difference:The linear separation between two points of

wave is called Path difference.It is measured in mm or cm.

Principle of superposition:

Interference:

Destructive Interference : Constructive Interference :