On the other hand, if the slit is narrow, the light can be spectacularly diffracted. As a result, a bright spot is illuminated on the screen. The light will pass without touching if the slit’s width is very large. When the wavelength of the light is larger or similar to the obstacle, there produces a diffraction pattern. Two conditions need to be fulfilled to ensure the phenomenon is observable. We call this diffraction pattern because the light is diffracted (where it is painted). But, unlike the pattern produced by two slits, the light’s intensity does not seem to be distributed evenly in a single slit. It is a phenomenal discovery because it also helps produce the pattern using a single slit. The addition doubled the region’s luminosity while the negation rendered the region fully dark. In addition, when a ripple peak interferes destructively with another one, it can form a dark band. Here, one ripple’s peak interferes with another’s. He said such a pattern could only be formed by waves interfering with one another.Ī bright band is created while squeezing two waves between the slits. He proved that it is impossible to bend light or make it flow around an obstacle unless it obeys the Huygens principle. This discovery by Thomas Young vindicated Huygens. We call squeezed light an interference pattern, which can be seen as a uniform, alternating pattern of dark and bright bands. He made light squeeze through two slits kept adjacent to one another. However, he failed to illustrate the light’s wave nature, making it impossible for him to claim his achievement experimentally.Īfter nearly a decade, there came Thomas Young, a very enthusiastic British polymath who successfully illustrated the behaviour of light. He postulated a principle named Huygens’ Principle, stating that each point on a light wave could act as a source for a secondary wave capable of travelling at the same speed as light.įurthermore, he managed to explain the optical phenomena occurrence, namely reflection and refraction, using his light wave theory. His statement was contradictory to Newton’s beliefs. He suggested that the light behaves like a wave. In the 17 th century, a Dutch mathematician named Christian Huygens declared that light is not capable of behaving like a particle. This article will deeply discuss the diffraction phenomenon while explaining other related concepts and topics. In many cases, especially when an obstacle is very large, the stream of light does not flow around it. Moreover, it does not necessarily mean that the light stream must flow around the obstacle. Here, the light acts like water, which flows around the obstruction to reach our eyes. What is diffraction? Diffraction is the phenomenon that enables the light radiated by a source to be easily detectable even though there is an obstacle in between. Comparison Fresnel Diffractionġ If the screen and the source of light is at a finite distance from the obstacle, then the diffraction is called Fresnel diffraction.ġ If the source of light and screen is at an infinite distance from the obstacle then the diffraction is called Fraunhofer diffraction.Ģ To obtain Fresnel diffraction, zone plates are used.Ģ To obtain Fraunhofer diffraction, the single-double plane diffraction grating is used.ģ The waterfronts falling on the obstacle in case of Fresnel diffraction are not plane.ģ The wavefronts falling on the obstacle in case of Fraunhofer diffraction are planes.Ĥ No convex lens is needed to converge spherical wavefronts.Ĥ Plane diffracting wavefronts are converged via a convex lens.Diffraction, polarisation and interference are the three major concepts essential for light wave nature. The pattern observed is a fringed image of the source and in a particular direction. Fraunhofer Diffraction: Fraunhofer diffraction occurs with plane wave-fronts with the object situated at infinity. The waves are spherical and the pattern observed is a fringed image of the object.Ģ. Fresnel Diffraction: Fresnel diffraction occurs when light from a point source meets an obstacle. Whereas if the two are closer in size or equal, the amount of bending is noticeable and can be easily seen with the naked eye. So If the opening is greater than the wavelength of light, the bending will be almost negligible. But the proportion of bending depends on the relative size of the wavelength of light to the size of the opening. We can define Diffraction as bending of light when it passes around the edge of an object. When the light falls on the obstacle whose size is comparable with the wavelength of light then the light bends around the obstacle and enters the geometrical shadow.
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