Question

In an isotropic medium the secondary wavelets centred on every point of a given wave front are all

Answer 1

Explanation:

(1)When a disturbance is caused in a medium, the particles of the medium start vibrating. The surface in the medium, on which each particle vibrates in same phase, is called the wave front. In a homogeneous medium, the wave front is normal to the direction of propagation of the wave. If the source is like a point at a finite distance, the wave front is always spherical. If the source is very far (i.e. at infinite distance) the wave front is plane. If the source is in form of a slit at a finite distance, the wave front is cylindrical.

(ii) Every point of the medium on a given wave front is a centre of originating new disturbance. This new disturbance is called the secondary wavelet. If the medium is homogeneous, the secondary wavelets travel with the same speed as the speed with which the original wave front travels.

(iii) The common tangential surface (or envelope) drawn on these secondary wavelets at any instant, represents the position of new wave front at that instant.

For example in Fig. (a) let AB be the position of spherical wave front at any instant originated from a point source S. According to Huygen's principle, secondary wavelets are given out from each particle of medium on this wave front AB, which travel forward with the speed v of the original wave front. Hence to obtain the position of new wave front after time t, draw spheres of radius vt with such point a, b, c, d..... of the wave front AB as centre.

Answer 2

Answer:

In an isotropic medium the secondary wavelets centred on every point of a given wave front are all spherical.

Explanation:

• Huygens's Principle states that every point on a wavefront is a source of secondary wavelets, which spread forward at the same speed.

• Thus is enables to find the position of wavefront.Every point on a wave-front may be considered a source of secondary spherical wavelets which spread out in the forward direction at the speed of light.
• The new wave-front is the tangential surface to all of these secondary wavelets.