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Path of Light

Introduction

Light is a form of energy that is propagated through electromagnetic waves. Light thus constantly changes from electric to magnetic properties and is therefore considered as having a twofold nature. In some instances it is propagated as waves while in other instances it is propagated in particle form referred to as photons (Feynman, Robert and Matthew). Light bears no mass and constantly moves through space at the speed of light which is the highest speed governed by the laws of physics. As much as light bears no mass, it bears both momentum and energy. Light will always adopt a path that will use up the least time possible as is supported by the Fermat’s principle (Spring and Davidson).

Fermat’s principle

Fermat’s principle lay down the rules that determine the least time path that light will travel in. Fermat’s principle also serves to comprehensively explain other light phenomenon such as refraction, reflection, diffraction dispersion, light scattering, as well as color absorption. It is important to note that light hardly moves in paths that are straight (Spring and Davidson). This is due to the fact that as photons move through matter, they tend to interact with the many electrons contained in the medium through which these photons move. As such, the duration of time it takes for electrons and photons to interact principally determines the actual path that light will follow.

For instance, blue light which has the highest frequency is refracted at a higher degree compared to red which has the lowest frequency (The Physics Classroom). Due to the high frequency exhibited by blue light, it tends to take more time in interacting with the electrons in the medium through which it is propagated. The least time path for blue light requires it to bend more than red light as blue takes more time to interact with electrons in the medium than red (Feynman, Robert and Matthew). This is achieved so as to enable blue to move from such interactions at a faster rate. This is the same behavior that is exhibited in the way different colors of the rainbow tend to bend at different degrees.

Key concepts defining the path of light

Light energy is a produced when the rate of acceleration on charged particles is increased causing the electromagnetic fields to radiate energy outwards in the form of light. The electromagnetic field around positively accelerating and oscillating charged particles is what is referred to as light. Light is therefore a form of electromagnetic radiation.

Light has many colors. The color of light is determined by the electromagnetic radiation’s frequency. Light is both visible and invisible. Invisible light is in the form of ultraviolet radiation, x-ray radiation or gamma-ray radiation (The Physics Classroom). Visible light is in the form of red, green, blue, and violet. Invisible light has very short wavelength with the gamma ray radiation having the shortest wavelength range. As for visible light, red has the longest wavelength range while violet has the shortest wavelength range (Feynman, Robert and Matthew). The longer the wavelength, the shorter frequency and one can therefore postulate that the shorter the frequency the more intense the red hue emitted by light. Visible light is only visible to human beings as vision is limited to the wavelengths that define violet and red.

Reflection

It is now common knowledge that light moves in the shorts time path which in a geometrical point of view is a as a straight line. However this is only truly achievable if light moves in a vacuum. Interactions with electrons of the medium through which it is propagated tend to cause light to bend in an attempt to realize the shortest time path maxim (Spring and Davidson). Light also bears specific characteristics depending on the surface on which it falls on.

The most common means with which to comprehensively understand reflection is through the study of the behaviors exhibited by light when it strikes a mirror. There is one main reason as to why mirrors are the preferred objects for use in the study of light’s characteristics relative to reflection (Feynman, Robert and Matthew). When light falls on a mirror, it ceases to move in the shortest time path but bounces of the surface of the mirror taking a different path. The path of reflected light changes proportionally to the angle at which light hits the mirror’s reflective surface.

The reflected light’s path is explained by one of the simplest relations in the world of physics. The angle between the original light path and the mirror also referred to as the incidence ray is equal to the angle between the mirror and the reflected ray (Spring and Davidson). This is the postulate for the law of reflection which states that the angle of the incidence ray is equal to the angle of the reflected angle (Feynman, Robert and Matthew).

Refraction

As earlier noted, light bends as a result of the resultant interactions between electromagnetic radiation and the electrons present in the medium through which it travels. When light moves from one medium to another as with air and glass, one observes a rather queer phenomenon. Light tends to bend in a rather explicit manner such that, it is clearly visible that light does not in such an instance move in a straight line (The Physics Classroom).

When the angle with which the incidence ray or the original light path travelling through air meets a different medium such as water is almost at a 90 degree angle to the water, the bend is not quite pronounced. However, if the angle of the incident ray to the water surface is small, the bend is quite pronounced. The angle at which the incident ray bends is referred to as the breakage angle. The 17th Century Dutch Mathematician known as Willebrord Snell came with a law that related the incidence angle for the path of light in a different medium and the refracted ray in the second medium (Feynman, Robert and Matthew). He calculated that angle A, the angle in medium A and angle B is the refracted angle in medium B, then the sine of angle A is equal to the sine of angle B multiplied by a constant. This is aptly referred to as Snell’s law.

Snell’s law provides that light tends to travel faster when it propagates through mediums with diminishing refractive indexes. The refractive index is the constant arrived at through the application of Snell’s law. As explained earlier, light bends when it travels through a medium as photons and the mediums electrons interrelate (Spring and Davidson). Fermat’s principle supports this phenomenon that results in light changing its direction. It can be explained that light bends when travelling in a medium like glass. This is because interactions between its electrons and photons require light to travel in a more straight line in accordance with the least time path principle (The Physics Classroom). As such, it tends to travel in a more straight line when moving through mediums which decrease its speed. This is what gives rise to the refraction or bending of light.

Colors

What is perceived as white light is a conglomeration of all lights that are visible to man, that is violet, red, indigo, orange, yellow, blue, and green. It is important to point out that black is the human eyes’ perception relative to the lack of light (The Physics Classroom). What differentiate these colors are the different frequencies that qualify various colors. As such each color will move with a different frequency and when white light moves from one medium to another, then the difference in speed leads each color to bend at a different angle (Feynman, Robert and Matthew). The slower the color the more it have to travel faster in the second medium. This same principle gives rise to rainbows observed when sunlight is refracted by raindrops.

Applications of the path of light

There is a phenomenon referred to as total internal reflection where light is refracted to such a degree that it refracts back to the first medium trapping the light within it. This is the same principle through which fiber optic cables operate. Mirrors also apply the path of light phenomenon to benefit mankind in a myriad of ways as the salon, barber shop, rear view mirrors, periscopes just to name but a few. Lenses are made out of curved glass which can either focus light to or away from a screen. Those which tend to focus light to a specific point on a screen are referred to as convex lenses (Feynman, Robert and Matthew). Those that have the opposite effect are referred to as concave lenses. The applications of the path of light have played significant roles in the development of science through telescopes for astrology and microscopes for medicine and biology.

Work cited

Feynman, Richard Phillips, Robert B. Leighton, and Matthew Sands. The Feynman Lectures on Physics, Volume I: Mainly Mechanics, Radiation, and Heat. Vol. 1. Arizona: Basic Books, 2011.

Spring, Kenneth, R, and Davidson, Michael, W. “Light: Particle or a Wave?” Olympus America Inc, 2012. Web. 7 June 2013.

The Physics Classroom. Refraction and Ray Model of Light, 2013. Web. 7 June 2013.