wave optics

Question 1

the speed of the wave.

Answer 1

The speed with which the wavefront moves outwards from the
source is called the speed of the wave.

Question 1

wavefront

Answer 1

a locus of points, which oscillate in phase is called a
wavefront; thus a wavefront is defined as a surface of constant
phase.

Question 2

The energy of the wave travels
in a direction _____ to the wavefront.

Answer 2

perpendicular

Question 3

spherical wave

Answer 3

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

Question 4

plane wave

Answer 4

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

Question 5

Huygens principle is essentially a geometrical construction. justify

Answer 5

Huygens principle is essentially a geometrical construction,
which given the shape of the wafefront at any time allows us to determine
the shape of the wavefront at a later time

Question 6

Huygens principle

Answer 6

according to Huygens principle, each point of the
wavefront is the source of a secondary disturbance and the wavelets
emanating from these points spread out in all directions with the speed
of the wave. These wavelets emanating from the wavefront are usually
referred to as secondary wavelets and if we draw a common tangent
to all these spheres, we obtain the new position of the wavefront at a
later time.

Question 7

how could Huygens could
explain the absence of the backwave?

Answer 7

Huygens argued that the amplitude of the
secondary wavelets is maximum in the forward direction and zero in the
backward direction; by making this adhoc assumption, Huygens could
explain the absence of the backwave. However, this adhoc assumption is
not satisfactory and the absence of the backwave is really justified from
more rigorous wave theory.