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?

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