Destructive Interference

To understand the concept of destructive interference we should first know what is the interference of light? When two waves meet one another, they are said to have interfered. Interference can be defined in simple words as the process in which 2 separate waves superpose with one another for forming a resultant wave. This resultant wave can have higher, equal, or even lower amplitude. Interference is mostly seen to be of two main types namely Destructive interference and constructive interference. In constructive interference, the two waves are seen to interfere in the same direction. Throughout this article, discussions will be done concerning destructive interference.

Destructive interference 

Destructive interference can occur in a light wave, sound wave, or any other type of wave. Destructive interference of light specifically occurs when two waves of light meet the outside phase. This essentially means that the resultant light’s intensity destructive interference of light gets reduced. In simple words, destructive interference is seen to happen when two waves meet in a manner such that they completely cancel out each other. Hence, for two waves to interfere destructively, they need to have similar amplitude and should travel in the opposite direction. In this context, it should be mentioned that due to destructive interference the two waves may not always cancel each other out. When the two waves of comparable frequency travel in a particular medium superpose. The resultant at separate positions are separate from the addition of their intensities. This is due to superposition. At some points, the intensities are too less or even negligible and this is known as destructive interference. 

The formula for destructive interference

There are some specific formulas concerning destructive interference. These have been outlined in the following.

• The path difference of the two interfering waves is always a specific odd multiple of λ/2

Hence, Δ = λ/2 (2n – 1), where Δ is the path difference and λ is the wavelength.

• The difference in phase between the two particular waves is given as the π’s odd multiple. Hence mathematically the phase difference is given as π (2n – 1).
• Lastly, the interval of time between the two waves is given as an odd multiple of the time/2. Hence, mathematically θ = T/2 (2n – 1). Where θ = time interval and T = period.

Difference between destructive interference and constructive interference

In most simple words, two waves that cancel each other are known as destructive interference. On the other hand when the two waves combine to form a smaller wave then it is known as destructive interference. Secondly, the amplitude of the resultant wave in the case of constructive interference is more than each of the interfering waves, whereas in destructive interference upon interference the amplitude of the resultant wave is smaller than each of the interfering waves. Moreover, constructive interference occurs when the two waves meet in the same direction and the resultant waves also move in the same direction, while in destructive interference the two waves interfere from the opposite direction. Lastly, when the two waves interfere constructively, their crests are seen to align together. However, in the case of the destructive trough of one wave aligns with the crest of another wave.

Destructive interference examples

In nature, there are many instances in which destructive interference is visible. Some of these instances have been outlined in the following. 

• The interference of light beams is an example of destructive interference.
• The interference of gravitational waves can also be regarded as destructive interference.
• Radio waves as well as moving electrons are an important example of destructive interference. 

Conclusion 

The entire article has been written to highlight some key points of destructive interference. Interference is a core topic in the subject of physics. However, it also has high importance in the subject of chemistry. The topic has immense importance for the UPSC exam. Throughout the article, it has been identified that interference of two separate types. These are constructive interference and destructive interference. The article mostly focuses on destructive interference and this is properly discussed through destructive interference of light, interference pattern, and the analyzing the key question that is what is the interference of light?