Explanation:explanation none

We know that,
Phase difference=K ×path difference. K=2 π/ λ.
Therefore, phase difference=(2 π/ λ) ×( λ/3)=2 π/3=120 degree.

Brewster 's angle is an angle of incidence at which light with a particular polarization is perfectly transmitted through a transparent dielectric surface, with no reflection. When unpolarized light is incident at this angle, the light that is reflected from the surface is therefore perfectly polarized.

(a) Speed of light in glass is  c/μ=2 ×10⁸ m/s

(b) The speed of light in glass is not independent of the colour of light. The refractive index of a violet component of white light is greater than the refractive  index of a red component. Hence, the speed of violet light is less than the speed of red  light in glass. Hence, violet light travels slower than red light in a glass prism.

When we use white light, the central bright will have light from all wavelengths as none of them cancel out. Hence the central bright fringe appears white.
For other bright fringes, depending on the wavelength of light constructive interference will not take place for certain wavelengths. Hence they will not be white, rather will be coloured, hence differentiated from central fringe.

Light as a wave: Light can be described (modeled) as an electromagnetic wave. In this model, a changing electric field creates a changing magnetic field. This changing magnetic field then creates a changing electric field and BOOM - you have light. Unlike many other waves (sound, water waves, waves in a football stadium), light does not need a medium to “wave ”in.

The process by which a beam of light or other system of waves is spread out as a result of passing through a narrow aperture or across an edge, typically accompanied by interference between the waveforms produced.

The shape of the wave front in case of a light diverging from a point source is spherical and is shown in the given figure. The shape of the wavefront in case of a light emerging out of a convex lens when a point source is placed at its focus is a parallel grid.

The Particle Model of emission and absorption is based on the idea that light is composed of discrete particles called photons , and these photons carry quantized energy. This model helps us understand how atoms and molecules interact with light by either emitting or absorbing photons during electronic transitions.

Distance between the slits, d=0.28 ×10 −3  m

Distance between the slits and the screen, D=1.4m

Distance between the central fringe and the fourth  (n=4) fringe, 

u=1.2 ×10 −2  m

In case of a constructive interference, we have the relation for the distance between the two fringes as:

u=n λD/d

⇒λ=ud/nD=6 ×10 −7m=600nm