Wave Optics: Diffraction of Light

Question 1

Diffraction

Answer 1

The bending of light round the corners of the obstacles, or apertures, is called diffraction

Question 2

What is the diffraction pattern of a single slit

Answer 2

A central bright band, having on both sides narrower, alternately dark and bright bands of decreasing intensity

Question 2

What happens on decreasing the slit width

Answer 2

The diffraction pattern becomes broader and the central band is wider

Question 3

What happens on increasing the slit width

Answer 3

The diffraction pattern becomes narrower and the central band also becomes narrower

After a certain limit, a thin line appears, i.e. the propagation of light becomes approx rectilinear (difffraction nealy vanishes)

Question 4

When does diffraction take place

Answer 4

When the slit width/diffracting obstacle is of the order of the wavelength of the wave i.e. e ≈ λ

Question 5

What is angular width of central maximum

Answer 5

The angular position between the first minima on the two sides of central maximum

W = 2sin^-1(λ/e)

Question 6

Difference b/w interference and diffraction

Answer 6

Interference
1. Deue to superposition of light waves from two coherent sources
2. Interference fringes may or may not be of the same width
3. In interference pattern, all bright fringes are of same intensity
4. In interference pattern, the intensity at minima is usually zero or very small adn there is good contrast b/w bright and dark fringes

Diffraction
1. Due to interference of secondary wavelets coming from different points of the same wavefront
2. Diffraction fringes are never of the same wifth
3. In diffraction pattern, the intensity of successive bright fringes goes on decreasing.
4. In diffraction pattern, intensity at minima is never zero and there is poor contrast b/w bright and dark fringes