Question

Identify the correct statement from the following

• A. A monochromatic ray of light after passing through the prism should create a spectrum of seven colors
• B. Wave nature of light was proposed by Huygens
• C. Huygen’s wave theory could not explain the phenomenon of reflection
• D. The direction of the light ray and its wavefront are opposite

Answer 1

The correct option is B

Wave nature of light was proposed by Huygens

Explanation for correct option:

Option (B):

1. The idea of the wave nature of light was first put forward by Christian Huygen in $1690$.
2. According to him, a beam of light consists of longitudinal pulses which propagate as compressions and rarefactions through a medium, just like sound waves.
3. As light can propagate through a vacuum the supporters of the wave theory of light postulated the presence of an all-pervading ether medium.

Explanation for Incorrect Options:

Option (A):

1. Monochromatic light ray means a ray of light that consists of only one colour or wavelength.
2. Therefore, when it passes through a prism it will not general several other colours as there is only one colour present.

Option (C):

1. According to Huygen's principle in a homogeneous and isotropic medium, every point of a primary wavefront serves as the source of spherical secondary wavelets that travel with a speed and frequency equal to those of the primary wave.
2. The wavefront at some later instant of time is the envelope of these wavelets.
3. The angle of incidence is the angle that the incident plane wavefront makes with the surface.
4. Similarly, the angle of reflection will be the angle that the reflected plane wavefront makes with the surface.
5. It has been proved that the incident way, the reflected ray and the normal at the point of incidence lie in one plane, and the angle of incidence is equal to the angle of reflection.
6. Hence, Huygen's wave theory could prove the laws of reflection.

Option (D):

1. A wavefront is a surface upon which the phase of disturbance is the same at any given instant of time.
2. It is the loci of points of constant phase.
3. A wave travels in a direction normal to the wavefront.
4. Hence, the direction of the light ray and its wavefront are not opposite.

Hence, the correct answer is option (B).