Light Rays' Fascinating Journey From A Candle

Light is the energy that makes it possible for us to see. Light rays emitted by a candle are generated by the temperature of the flame, which is made up of the emissions of a black body at this temperature and the emissions of the chemical elements that make up the candle. When you light a candle, the heat of the flame melts the wax near the wick, and this liquid wax is then drawn up the wick by capillary action. The heat of the flame vaporizes the liquid wax and starts to break down the hydrocarbons into molecules of hydrogen and carbon. These molecules are then drawn into the flame, where they react with oxygen from the air to create heat, light, water vapour, and carbon dioxide. The light given off by a candle is the result of the ignition of carbon particles, which emit a full spectrum of visible light.

The speed of light

The first quantitative estimate of the speed of light was made by Ole Rømer in 1676 by studying the motion of Jupiter's moon Io. Over time, scientists like Hippolyte Fizeau and Léon Foucault improved the accuracy of these measurements, and in 1983, the speed of light was defined as an exact value of 299,792,458 metres per second.

Reflection and refraction

When light rays are emitted by a candle, they travel in a straight line—unless they are reflected or refracted.

Reflection occurs when light bounces back from a surface in the same medium without being absorbed. This happens on shiny surfaces that do not allow light to penetrate through them. Reflection can be of two types: regular (or specular) reflection and diffuse reflection. Regular reflection occurs on smooth, polished surfaces, such as mirrors, where light is reflected in a single direction. Diffuse reflection occurs on rough surfaces, where light is reflected in multiple directions, creating a distorted image or no image at all.

Refraction, on the other hand, is the bending of light rays when they pass from one medium to another. This occurs on transparent surfaces, where light is allowed to bend into a different medium. Refraction causes a change in the direction and speed of light as it enters a new medium. The denser the medium, the slower the speed of light, and vice versa.

The angle of reflection in the case of regular reflection is the same as the angle of incidence. In refraction, however, the angle of reflection and the angle of incidence are not the same.

The phenomenon of refraction can be observed in various situations, such as when an object is partially submerged in water, or when mirages occur in a hot, sandy desert.

Both reflection and refraction play a crucial role in explaining how people see images, colours, and even optical illusions.

Light as electromagnetic waves

Light is an electromagnetic wave made up of electrical and magnetic forces that travel through space at a very high speed. Electromagnetic waves are emitted by electrically charged particles undergoing acceleration, and these waves can subsequently interact with other charged particles, exerting force on them.

Electromagnetic waves can travel through a vacuum, such as the vacuum of space, as well as through air and solid materials. They differ from mechanical waves in that they do not require a medium to propagate.

Electromagnetic waves are classically defined as synchronized oscillations of electric and magnetic fields. The position of an electromagnetic wave within the electromagnetic spectrum can be determined by its frequency of oscillation or its wavelength. Electromagnetic waves of different frequencies are called by different names as they have different sources and effects on matter. In order of increasing frequency and decreasing wavelength, the electromagnetic spectrum includes radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, and gamma rays.

The energy in electromagnetic waves is sometimes referred to as radiant energy. Light, electromagnetic waves, and radiation all refer to the same physical phenomenon: electromagnetic energy. This energy can be described by frequency, wavelength, or energy.

Light as particles

Light can be considered to consist of tiny packages of energy called photons. Photons are the smallest possible particles of electromagnetic energy and, therefore, also the smallest possible particles of light. They carry electromagnetic energy, including visible light, and many other types of lower- and higher-energy forms of energy. Photons are massless and can travel at the speed of light.

Photons are emitted in many natural processes. For example, when a charge is accelerated, it emits synchrotron radiation. During a molecular, atomic, or nuclear transition to a lower energy level, photons of various energy are emitted, ranging from radio waves to gamma rays. Photons can also be emitted when a particle and its corresponding antiparticle are annihilated.

Photons can be absorbed by matter, and when this happens, their light is transformed into heat, warming the matter. This is how sunlight warms things on Earth. Photons can also be scattered by matter. For example, photons scatter so many times in the solar radiative zone after leaving the Sun's core that radiant energy takes about a million years to reach the convection zone.

Photons carry a fixed amount of energy, and their energy depends on their wavelength. Longer-wavelength photons have less energy, and shorter-wavelength photons have more. For example, red photons have less energy than blue photons.

Photons also have the characteristics of both waves and particles, known as wave-particle duality. This was a key part of the development of quantum mechanics.

Inverse square law

The Inverse Square Law is a fundamental principle in physics that describes the behaviour of light intensity with respect to distance from a point light source. The law states that the intensity of light or illuminance from a point source decreases as the square of the distance from the source increases. In other words, as the distance from the light source increases, the light spreads over a larger area, reducing its intensity at any given point.

The Inverse Square Law can be expressed mathematically as:

> {\displaystyle {\text{intensity}}\ \propto \ {\frac {1}{{\text{distance}}^{2}}}\,}

Or as:

> {\displaystyle {\frac {{\text{intensity}}_{1}}{{\text{intensity}}_{2}}}={\frac {{\text{distance}}_{2}^{2}}{{\text{distance}}_{1}^{2}}}}

This means that if the distance between an object and a light source is doubled, the given area will experience only one-fourth of the light from the source.

The Inverse Square Law is applicable in several fields. For instance, in photography, it is used to calculate proper exposure settings to ensure well-exposed photos. In astronomy, it is used to understand the brightness of stars and other celestial objects, helping determine their distance from Earth. The law is also used in lighting design to ensure sufficient and uniform illumination in indoor and outdoor settings.

The Inverse Square Law is not limited to light; it also applies to other phenomena such as gravitation, electric, sound, and radiation.

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