Physics assignment Paper 1 (Important questions)

QUESTION:1

 Explain the fermet's Principle

Fermat's principle, also known as the principle of least time, is the link between ray optics and wave optics. In its original "strong" form, Fermat's principle states that the path taken by a ray between two given points is the path that can be traversed in the least time. In order to be true in all cases, this statement must be weakened by replacing the "least" time with a time that is "stationary" with respect to variations of the path — so that a deviation in the path causes, at most, a second-order change in the traversal time. To put it loosely, a ray path is surrounded by close paths that can be traversed in very close times. It can be shown that this technical definition corresponds to more intuitive notions of a ray, such as a line of sight or the path of a narrow beam.

QUESTION:2

Find the Resultants Amplitude and Intensity of the Principle of Superposition

Intensity if the power transferred per unit area that is perpendicular to the direction of propagation of the energy. Intensity is directly proportional to square root of the amplitude. So, if intensity becomes double, then amplitude will become four times. Let us consider two waves that have the same frequency but have a certain fixed phase difference between them. Their super position shown below

Let the two waves are:

y₁ = a₁ sin ωt and y₂ = a₂ sin (ωt + φ)

Where,

a₁, a₂ = Individual amplitudes

φ = Phase difference between the waves at an instant when they are meeting a point.

(i) Resultant Amplitude: The resultant wave can be written as: y = A sin (ωt + φ).

Where, A = Resultant Amplitude = √(a₁² + a₂² + 2a₁a₂ cosφ)

(ii) Resultant Intensity: As we know Intensity α (Amplitude) 2

I₁ = ka₁²; I₂ = ka₂² and I = kA² (k is a proportionality constant)

Resultant Intensity (I) = I₁ + I₂ + 2√I₁I₂ cosφ

For two identical sources, I₁ = I₂ = I₀ ⇒ I = I₀ + I₀ + 2√I₀I₀ cosφ = 4 I₀ cos² (φ/2).

QUESTION:3

Explain the Fresnd's theory of half period zones

According to Fresnel's the entire wave front can be divided into a large number of parts of zones which are known as Fresnel's half period zones (HPZ's). The resultant effect at any point on screen is due to the combined effect of all the secondary waves from the various zones.

Suppose ABCD is a plane wave front. We desire to find it's effect at point P consider a sphere of radius (d+λ/2) with centre at P, then this sphere will cut the wave front in a circle (circle 1). This circular zone is called Fresnel's first (1) HPZ.
A sphere of radius b + 2(λ/2) with centre at P will cut the wave front in circle 2, the annular region between circle 2 and circle 1 is called second (II) HPZ.
The peripheral area enclosed between the nth circle and (n — 1)th circle is defined as nth HPZ.

QUESTION:4

Description of Linear, Circular and elliptical Polarization

Linear polarization: the electric field of light is confined to a single plane along the direction of propagation . 

Circular polarization: the electric field of light consists of two linear components that are perpendicular to each other, equal in amplitude, but have a phase difference of π/2.

Elliptical polarization: elliptical polarization is the polarization of electromagnetic radiation such that the tip of the electric field vector describes an ellipse in any fixed plane intersecting, and normal to, the direction of propagation.

QUESTION:5

Explain the He-Ne Laser

A Helium–Neon laser or He-Ne laser, is a type of gas laser whose gain medium consists of a mixture of 85% helium and 15% neon inside of a small electrical discharge. The best-known and most widely used HeNe laser operates at a wavelength of 6328 A^o, in the red part of the visible spectrum.