Wave Theory Of Light – History, Theory, Principle & Types

Introduction

According to the wave theory of light, a light source emits disturbances in all directions. When these waves transport energy, they reach the eye, stimulating the optic nerves and providing vision. Electromagnetic radiation within the portion of the electromagnetic spectrum visible to the eye is called light or visible light. Between the infrared and the bright regions, visible light is typically defined as having frequencies in the range of 400–700 nanometers (nm). In this article, you will learn about the wave theory of light, Huygen’s principle, the history of wave theory, and the advantages and disadvantages of Hyugen’s Principle.

What is the Wave Theory of Light?

Light is arranged as an electromagnetic wave according to the wave theory of light. This hypothesis considers light to be a spectrum of frequencies, some of which we can see (apparent light) and some of which we cannot (bright and infrared light).

Christian Huygens established the basic point-by-point wave concept of light, which allowed him to formulate the principles of reflection and refraction. He asserts that light is an uncomfortable effect emanating from the source and that its generation requires the movement of mechanical waves acting as longitudinal waves via an ether medium. After that, it proved false that ether existed in every space. This idea could no longer explain how light spread throughout spaces.

When dealing with light waves, the sine waveform is used. One complete sweep from 0 to 360 degrees makes up the waveform’s period. The wavelength and frequency of light waves are two crucial properties. The wavelength is the distance separating the wave’s peaks. Light waves have wavelengths that are on the order of nanometers.

The energy of light waves can be found out by the given formula,

E = hf,

where h is Planck’s constant equals 6.63 × 10^-34 Joule-Second and f is the frequency of the light wave.

The brief history of the Wave Theory of Light

Both scientists and thinkers have always been curious about light. In contrast to Christian Huygens’ assessment that light was constituted of waves flowing perpendicular to its direction of motion, Sir Isaac Newton offered the idea that light was composed of microscopic particles known as photons.

Huygens put out the concept that any location where a light disturbance intersects becomes a source of the spherical wave itself in 1678. The total of the secondary waves, which are the disturbance’s effects, also determines the shape of the new wave.

According to Max Planck, light is made up of discrete energy packets called light quanta that depend on the light’s frequency and velocity. In 1905, Einstein claimed that light has both particle and wave properties. He proposed that tiny particles known as photons are the building blocks of light. Quantum mechanics demonstrated the dual nature of light.

Huygen’s Wave Theory

Christiaan Huygens proposed the Huygens principle. He transformed the way we saw the light’s characteristics in 1678. The rectilinear theory of light, which says that light moves in straight lines, is something you have heard about. The Huygens principle is one of the most crucial methods for understanding diverse optical phenomena. The principle is an analytical technique that can be applied to resolve issues with wave propagation in the near-field limit, reflection, and diffraction.

Light enters a room through an opened window and permeates the area. Do you understand the cause of this? This is caused by how light spreads over space and has a wave-like quality. To further comprehend this, let’s examine Huygen’s Principle.

Huygen’s Principle

Huygen’s principle states, “Each point on a wavefront serves as a source for spherical wavelets that propagate ahead at the speed of light, i.e. 3 x 10⁸ m/s. These spherical wavelets are added together to generate the wavefront”.

However, this argument does not address the reason why refraction occurred in the first place. The second problem was that it needed to explain how light transmits energy as it travels. The Huygens Principle also called the Huygens-Fresnel Principle, emphasises the wave propagation behaviour in the manner described below:

• Secondary sources produce similar wavelets to those of the original source.
• The common tangent on the wavelets travelling forward at any given time determines the new wavefront.
• Wavefront refers to the collection of spherical wavelets.

Wavefront and Wave Normal

A wavefront is a location where waves arrive simultaneously at all points in a medium so that all locations have the same phase, such as light emitted by a bulb at a specific distance. A convex lens produces a plane wavefront when a point source of light is placed at its focal point.

A wave normal is a perpendicular line drawn towards the surface of a wavefront in the direction of the light propagation. Alternatively, a wavefront carries light energy parallel to the surface.

Types of Wavefronts

• Spherical wavefront
• Plane wavefront
• Cylindrical wavefront

Huygen’s Principle: Advantages and Disadvantages

Advantages:

• It could explain the laws of diffraction, interference, reflection, and others.
• The wave theory says that the speed of light would be slower in an optically denser medium than in an optically rarer one.

Disadvantages

• It was unable to explain how light propagated rectilinearly. According to Rectilinear Propagation of Light, light moves in a straight line.
• It was unable to explain the Raman effect, Compton effect, or photoelectric effect, as well as the polarisation of light and other phenomena. Later, the idea that light is a transverse wave was adjusted.
• Huygens presupposed the existence of an alleged medium (Ether). Using a device based on the principles of light beam interference, Michelson and Morley further researched the characteristics of the hypothetical ether. The experiment results showed no ether drag as the earth passed through it. Ether is not accurate, as demonstrated by these and other investigations.

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