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Introduction
To understand how light waves interact with objects like tiny holes or thin films, you need to know how light waves work. It is certain that when two waves interact, they may interfere with one another. This interference of light may be constructive or destructive when you combine two waves, the areas where the peaks of one match the peaks of the other will be added together.
What Is Interference Of Light?
The phenomenon of two light waves superposing to create a new wave with a larger, smaller or the same amplitude is known as interference of light waves. Thomas Young discovered the phenomena of light interference in 1801 AD.
When two or more light rays of the same frequency, wavelength and amplitude collide in a medium, the effect is cancelled or enhanced. This is referred to as interference of light waves.”
The concept of interference between two waves is quite straightforward. Furthermore, it is significantly simpler to calculate. To obtain the resultant wave, combine each point that appears in the same location on each wave. Interference effects are observed for many waves, including light, gravity waves, sound, matter and surface water waves.
History
Christiaan Huygens proposed the light wave theory. According to Huygens, light is composed of waves that vibrate up and down perpendicularly to the direction of the light. However, this hypothesis was not easily accepted because it opposed Sir Isaac Newton’s particle theory or corpuscular theory of light. According to Isaac Newton, light is composed of microscopic particles. The hypothesis of light waves was not widely accepted in the beginning.
In later years, another researcher named Thomas Young did the renowned Interference of Light experiment, also known as the Young’s Double Slit Experiment (YDSE). This experiment revealed that light is a wave.
Following this, a few other tests were carried out, including those involving the patterns of interference, diffraction and polarisation. These tests can only be explained in terms of light’s wave nature. Thus, wave theory was developed. The corpuscular hypothesis could not demonstrate a wide range of optical phenomena, including interference, diffraction, polarisation, dispersion and many more.
Interference of Light Types
The interference of light phenomenon can be divided into two broad categories:
The interference of light types can take the form of either constructive or destructive interference, depending on the situation.
- Constructive Interference
This happens when two waves of light superpose on top of each other. When this happens, one wave’s peak falls on the crest of another wave and the trough of another wave falls on its trough. This makes the resultant wave have more amplitude and intensity. This is referred to as constructive interference.
Some of its consequences include:
- Two light waves reinforce one another in constructive interference.
- A bright fringe can be seen on the screen due to constructive interference.
- Destructive Interference
In case of destructive interference, whenever two light waves are superimposed so that their crests and troughs coincide, the resultant wave’s amplitude and intensity is zero.
Several of its consequences include the following:
- Two waves cancel out each other’s effects.
- A dark fringe appears on the screen as a result of this.
Conditions for Interference
The conditions for observing light wave interference are as follows.
- It is necessary to have coherent sources of light.
- The amplitudes and intensities of the signals must be almost equivalent to provide sufficient contrast between the maxima and minima.
- The light source would have to be small enough to be termed a point source.
- The sources of interference must be close enough to each other to produce wider fringes.
- The distance between the source and the screen must be sufficient to create wide fringes.
- The polarisation of the light must be the same for each source.
- Monochromatic light sources are required.
Pattern of Interference
The result of constructive interference is bright bands, whereas destructive interference is dark bands. These are referred to as Fringes. The interference pattern is formed due to the creation of bright and dark areas on the screen.It has two slits that act as two sources of light.
Young’s Double Slit Experiment (YDSE)
Thomas Young conducted the YDS experiment, a well-known interference of Light experiment. This experiment established the wave theory of light. Thomas Young used a single light source and passed this through the two slits to create two coherent sources. As a result, each slit acts as a source of light.
S1 and S2 are two slits on a screen very close to one another. The slits are parallel. Other small slits place special emphasis on these areas. When the light from S1 and S2 spreads out, it hits a screen. In a situation where both slits are opened, the development of interference fringes occurs. When two waves have a path difference, they interfere constructively, Δ = λ, 2λ…. Nλ. When two waves have a path difference, they interfere destructively, Δ = λ/2, 3λ/2 …. (2n+1) λ/2.
Conclusion
The wave nature of light can be proven by optical interference. T. Young’s (1773–1829) famous double-slit experiment corroborated his interference hypothesis for light waves. It is critical to notice that the sources should continuously generate waves of the same wavelength during the same period. The two sources should also be close to one another. Observed interference patterns are stable if the waves are in coherence.
