Question

Which of the following nature of light waves is supported by the phenomenon of interference:
(A) Longitudinal
(B) Transverse
(C) Both transverse and longitudinal
(D) None of the above

Answer 1

Hint: Let us first understand the concept of interference. Interference is the phenomenon where two or more waves originating from a coherent source combine together to form alternate bright and dark fringes on a screen at a particular distance away from the source. There are two types of interference: constructive interference, and destructive interference.

Complete step by step solution:
Interference occurs in all types of waves, be it scalar waves like sound waves, or vector waves like waves in an elastic material.
For interference to occur there must necessarily be a wave and it should originate from a coherent source. Therefore the nature of light, or what kind of wave is a light wave cannot be determined using the phenomenon of interference.
We can observe interference of light that we know for a fact, possesses a transverse wave, by placing two small slits in front of a monochromatic source of light and letting the light pass from the slits to fall on a screen placed at a distance from the slits.
On the other hand, we can use a similar set up on water above which a ripple tank is placed. This ripple tank contains two point sources of simultaneous frequency that generate ripples in the water. These waves are longitudinal waves generating from a coherent source. When we place a screen in front of these waves, we get a similar interference pattern.
Therefore interference occurs in both transverse waves as well as in longitudinal waves.

Hence the correct answer is option (C) Both transverse and longitudinal.

Additional information:
In the case of polarization of waves, longitudinal waves can never be polarized. Only transverse waves can be polarized. Hence the transverse nature of light waves can be confirmed using the phenomenon of polarization.

Note: Even though interference cannot confirm the transverse wave nature of light, interference does confirm that light for a fact possesses a wave nature. Sir Thomas Young first confirmed the wave nature of light in 1807 from his Young’s Double Slit Experiment (YDSE). Before that most scientists believed in the Corpuscular nature of light laid down by Sir Isaac Newton.