In Young’s double-slit experiment using monochromatic light of wavelength \(\lambda,\) the intensity of light at a point on the screen where path difference \(\lambda\) is \(K\) units. What is the intensity of the light at a point where path difference is \(\lambda/3\)?
1. \(\frac K3\)
2. \(\frac K4\)
3. \(\frac K2\)
4. \(K\)

In a double-slit experiment the angular width of a fringe is found to be \(0.2^\circ\) on a screen placed \(1\) m away. The wavelength of light used is \(600\) nm. What will be the angular width of the fringe if the entire experimental apparatus is immersed in water?
(Take the refractive index of water to be \(4/3\)).
1. \(0.33^\circ\)
2. \(0.20^\circ\)
3. \(0.15^\circ\)
4. \(0.10^\circ\)

What is the Brewster angle for air to glass transition? (Refractive index of glass = 1.5.)

1. $49.{29}^0$
2. $43.{21}^0$
3. $50.{30}^0$
4. $56.{31}^0$

What is the distance for which ray optics is a good approximation for an aperture of 4 mm and wavelength 400 nm?

1. 40 m
2. 30 m
3. 20 m
4. 50 m

When the light diverges from a point source, the shape of the wavefront is:

1. Parabolic.

2. Plane.

3. Spherical.

4. Elliptical.

When the light is coming from a distant star that is intercepted by the earth, the shape of the wavefront is:

1. Spherical.
2. Plane.
3. Elliptical.
4. None of these.

Which of the following is not true?

A beam of light consisting of two wavelengths, 650 nm, and 520 nm, is used to obtain interference fringes in Young’s double-slit experiment. What is the distance of the third bright fringe on the screen from the central maximum for wavelength 650 nm?
1. \(1950 \frac{\mathrm{D}}{\mathrm{d}} \mathrm{nm}\)
2. \(1700 \frac{\mathrm{D}}{\mathrm{d}} \mathrm{nm}\)
3. \(1100 \frac{\mathrm{D}}{\mathrm{d}} \mathrm{nm}\)
4. \(1861 \frac{D}{d} n m\)

In deriving the single slit diffraction pattern, at which angles the intensity is zero?
1. \(\frac{2 n \lambda}{a}\)
2. \(\frac{n \lambda}{a}\)
3. \(\frac{n \lambda}{2 a}\)
4. \(0\)

A parallel beam of light of wavelength 500 nm falls on a narrow slit and the resulting diffraction pattern is observed on a screen 1 m away. It is observed that the first minimum is at a distance of 2.5 mm from the center of the screen. The width of the slit is:

1. 0.43 mm
2. 0.57 mm
3. 0.13 mm
4. 0.2 mm