By Huygen's wave theory of light, we cannot explain the phenomenon of:

If L is the coherence length and c the velocity of light, the coherent time is 

(1) cL

(2) $\frac{L}{c}$

(3) $\frac{c}{L}$

(4) $\frac{1}{Lc}$

Wavefront is:

1.  locus of all adjacent points at which the phase of vibration of a physical quantity associated with the wave in the same

2.  locus of all adjacent points at which the electric field is the same

3.  series of points on the wave with the same amplitude

4.  series of points on the wave with the same frequency

Huygens' wave theory allows us to know the:

Huygen's principle for secondary wavelets may be used to:

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:

The refractive index of glass is \(1.5\). What is the speed of light in glass? 
1. \(2 \times 10^{8}~\text{m/s}\)
2. \(3 \times 10^{8} ~\text{m/s}\)
3. \(1.5 \times 10^{8} ~\text{m/s}\)
4. \(2.2 \times 10^{8}~\text{m/s}\)

Which of the following is not true?

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.\(5.45 \times 10^{4} m/s\)