What type of wavefront will emerge from a (i) distant light source and (ii) point source?
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → (i) Plane; (ii) Spherical
A point source sends out light equally in all directions, so the points that the disturbance reaches at the same time lie on a sphere centred on the source: the wavefront is spherical. Far from the source the sphere has a very large radius, and a small part of it is practically flat, so a distant source gives a plane wavefront.
NCERT (2026-27):
Huygens Principle – “… If we have a point source emitting waves uniformly in all directions, then the locus of points which have the same amplitude and vibrate in the same phase are spheres and we have what is known as a spherical wave as shown in Fig. 10.1(a). At a large distance from the source, a small portion of the sphere can be considered as a plane and we have what is known as a plane wave [Fig. 10.1(b)].”