Table of Contents
Introduction
Huygens proposed a model in 1678 in which each point on a wavefront can be thought of as a source of waves expanding from that point. In a ripple tank, send plane waves toward a barrier with a small opening to demonstrate expanding waves. When waves approaching a beach collide with a barrier that has a small opening, the waves may be seen to expand from the opening. Huygens’ principle makes it easy to visualize refraction.
It is easy to see why the direction of light propagation changes if points on the wavefront at the boundary of a different medium serve as sources for the propagating light. The principle view of Huygens enabled visualization of how light could penetrate into the geometric shadow in a way that the particle view could not. Although Huygens’ principle was useful in establishing a wave rather than a particle view of light for ordinary optics, it left a number of unanswered questions. With its view of each point on a wavefront as a source, for example, it provided no explanation for why it did not propagate backward as well as forward. Miller and Fresnel expanded on the theory of light propagation to include diffraction. Kirchhoff improved the rigour of the light propagation theory.
The Huygens–Fresnel principle (named after Dutch physicist Christiaan Huygens and French physicist Augustin-Jean Fresnel) is an analytical method used to solve problems of wave propagation in the far-field limit, near-field diffraction, and reflection. It states that every point on a wavefront is a source of spherical wavelets, and secondary wavelets emanating from different points interfere with one another. The total of these spherical wavelets forms the wavefront.
Overview
Christiaan Huygens proposed the Huygens principle. In 1678, we had a new understanding of light and its properties. You’ve probably heard of the rectilinear theory of light, which states that light travels in straight lines. One of the most important methods for studying various optical phenomena is the Huygens principle. The principle is a method of analysis that is applied to wave propagation problems in the far-field limit, as well as near-field diffraction and reflection. It is stated that: “Every point on a wavefront is the source of spherical wavelets that spread out at the speed of light in the forward direction. The total of these spherical wavelets forms the wavefront.”
This theory, however, did not explain why refraction happened in the first place. Second, it was unable to explain how light transports energy as it travels. The Huygens Principle, also known as the Huygens–Fresnel principle, highlights the wave propagation behaviour described below: Secondary sources generate wavelets that are similar to the primary source’s.
The new wavefront is given at any given point in time by the common tangent on the wavelets in the forward direction.
The wavefront is formed by adding the spherical wavelets.
A plane light wave propagates through free space at the speed of light, c, according to Huygens’ principle. As shown in Figure the light rays associated with this wave-front propagate in straight lines. Using Huygens’ principle, it is also relatively simple to account for the laws of reflection and refraction.
According to Huygen’s principle, all points on the wavefront will become secondary sources. As a result, the wavefronts will move forward. Wavelets are emitted by all secondary sources. The new position of the waveform is the tangent drawn to all of the wavelets. The waves spread out in all directions. Previously, the water was at rest. However, as soon as we throw the stone into the water, the disturbance spreads in all directions within a few fractions of a second. In the water, ripples have formed. The ripples spread out and form a concentric circle around the disturbance.
The ripples are nothing more than the wavefront. The wavefronts spread out in all directions gradually. So we have a wave coming out of every point. The primary wavefront is formed, and then a secondary waveform is formed from the primary wavefront, and so on. The disruption does not last very long. It gradually fades as more and more waveforms are formed.
According to Huygen’s principle, every point on the wavefront can be thought of as a source of secondary spherical wavelets that spread out in the forward direction at the speed of light. The tangential surface to all of these secondary wavelets is the new wavefront. As a result, it is a geometrical method for determining the wavelength.
Wavefront and Huygens’ principle
A wavefront is a surface that has a constant phase when an optical wave passes over it. The surface over which a wave has its maximum (the peak of a water wave, for example) or minimum (the trough of the same wave) value is known as a wavefront. Huygens’ wave theory describes the wave nature of wave propagation.
When applied to lightwave propagation, this principle states: “Every point on a wavefront can be thought of as a source of secondary spherical wavelets that spread out at the speed of light in the forward direction. The tangential surface to all of these secondary wavelets is the new wave-front.”
State huygens principle
Huygens had a crucial insight into the nature of wave propagation, which is now known as the Huygens’ principle. When applied to lightwave propagation, this principle states: Every point on a wavefront can be thought of as a source of secondary spherical wavelets that spread out at the speed of light in the forward direction. The tangential surface to all of these secondary wavelets is the new wave-front.
Following the creation of the primary wavefront, each primary wavefront is followed by the creation of a secondary wavefront. Second, each point on the wavefront acts as a secondary source of light, emitting additional wavefronts. As a result, the effective wavefront produced is tangential to all of the secondary wavefronts produced by the secondary sources, as shown in the figure. A light wave propagates through space in this manner by generating secondary sources and wavefronts. The transverse direction is always perpendicular to the wavefronts.
Huygens wave theory
The Huygens Principle of Secondary Wavelets Principle is used to provide a qualitative explanation of both rectilinear and spherical wave propagation, and to derive the laws of reflection and refraction, however, it is unable to explain the rectilinear propagation derivations that occur when light hits edges, apertures, and screens, which are often referred to as diffraction effects. David A. B. Miller explained the resolution of the above-mentioned error in 1991. The resolution is that the source is a dipole, not a monopole as Huygens assumed that cancels in the reflected direction.
Christiaan Huygens proposed the wave theory of light, which stated that light is made up of waves that vibrate up and down perpendicular to the direction of light travel. Huygen’s theory, as stated above, fails to explain the photoelectric effect, Compton’s effect, and other phenomena.
When light passes through an aperture, every point on the light wave within the aperture can be regarded as a source, resulting in a circular wave that propagates outward from the aperture. As a result, the aperture generates a new wave source that propagates as a circular wavefront. The intensity is higher at the center of the wavefront and lowers at the edges. This explains the observed diffraction pattern and explains why a perfect image of the aperture is not created on a screen. This phenomenon occurs frequently in everyday life. If someone calls to you from another room, the sound appears to be coming from the doorway.
Also read: Earth’s Magnetic Field
FAQs
Why does sound bend around a building's corner but light does not?
Because the wavelength of visible light is in the order of 0.5 microns, or 0.0005 mm, the light will only diffract when passing through very small openings. Sound waves, on the other hand, have a wavelength of about one metre and diffract very easily. Sound waves can then bend around the corner as a result of this.
What conditions cause light to behave as a wave and as a particle?
When light interferes with objects many times larger than its wavelength, it behaves as a wave. When light interacts with objects that are comparable or smaller in size to its wavelength, it behaves as a particle.
What is the significance of the Huygens Principle?
The Huygens principle aids us in predicting and comprehending light's classical wave propagation.
