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

Two towers on top of two hills are 40 km apart. The line joining them passes 50 m above a hill halfway between the towers. What is the longest wavelength of radio waves, which can be sent between the towers without appreciable diffraction effects?

1. 11.23 cm
2. 12.5 cm
3. 10.02 cm
4. 13.87 cm

In a double-slit experiment using the light of wavelength \(600\) nm, the angular width of a fringe formed on a distant screen is \(0.1^\circ.\) What is the spacing between the two slits?
1. \(3.44 \times 10^{-4} \) m
2. \(2.54 \times 10^{-4} \) m
3. \(1.31 \times 10^{-4} \) m
4. \(2.01 \times 10^{-4}\) m

The 6563 Å ${\mathrm{H}}_{\mathrm{\alpha }}$ line emitted by hydrogen in a star is found to be red-shifted by 15 Å. The speed with which the star is receding from the Earth is:

1.\(6.87 \times 10^{5} m/s\)
2.\(4.75 \times 10^{4} m/s\)
3.\(3.20 \times 10^{5} m/s\)
4.\(5.45 \times 10^{4} m/s\)

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