The Sun is also a star.

Light: Useful Basic Physics You Need to Know

Light seen from the Sun.

What is light?

Light can be defined in a simple way as a form of energy. Using light, we can see the world around us. Not just in a physical sense but also biologically, light plays a dominant role in the functioning of a human/ organism. For example- plants use sunlight to produce food in the Photosynthesis process. We cannot imagine the world without light.

We sustain life on this Earth due to the heat and light produced by the Sun. Many wonder whether light is a particle or a wave. In physics, it can be represented as a particle and a wave, depending on the theory used to describe it. In some scenarios, light is better explained by the wave theory, and in some by the quantum theory, better described as a particle.

In this case, light is made of particles called photons. Albert Einstein was the first person to explain the photoelectric effect based on the particle nature of light. But the photons are considered to be having no mass. So, in simple words, light can be called photons.


Is light an electromagnetic wave?

According to the wave theory, light is a transverse electromagnetic wave consisting of electric and magnetic fields which oscillate and are perpendicular to each other. Electromagnetic radiation of any type is also known as light. Hence light possesses electromagnetic energy.

Visible light spans a tiny wavelength range in the electromagnetic spectrum. Of these, the red color has the highest wavelength and lowest frequency, whereas, for violet, it is vice versa. Just below the frequency of the visible light, there is infrared light and just above the frequency range of the visible light is ultraviolet radiation.

The picture shows the visible (light) emission spectrum of Chlorine.
The picture shows the visible emission spectrum of Chlorine.

What are the sources of light?

The light can originate from natural as well as artificial sources. Examples of natural sources include the Sun, the stars, moonlight, insects that emit light, phosphorus, lightning, chemical reactions, etc. Examples of artificial light sources include fluorescent lamps, blue LEDs, matchsticks, lightbulbs, etc. Light doesn’t need a medium to propagate; hence it travels in a vacuum for huge distances.

A LED (Light-emitting diode) emits green light.
A LED (Light-emitting diode) emits green light.

What are its properties?

The main properties of light are its intensity, frequency/wavelength, polarization, monochromaticity, and direction of propagation. When they are incident upon a medium or travel through them, they exhibit other properties such as reflection, refraction, diffraction, interference, dispersion, and scattering. The speed of light is also an important property in Physics.

In a vacuum, its value is approximately equal to 3,00,000 meters per second. According to Einstein’s Special Relativity theory, no object in the Universe can travel faster than light. Hence it is an absolute parameter in physics. Light also exhibits different types of effects when interacting with matter.

When the light is incident on a material, it ejects electrons from the material if the frequency of the incident light is greater than the threshold frequency of the material. This effect is called Photoelectric Effect.


How is it created?

Light is created when an atom or a nucleus goes from a higher to a lower energy state. The difference in energy is emitted as light. For example, the light in Sun originated from nuclear fusion, i.e., mass was converted to light energy. Hence to create light, you need either an electric charge in accelerated/ oscillating motion or mass-energy equivalence.

The creation of light in an atom.

Keywords: Light, speed of light, properties, sources, characteristics, energy, wave, speed, reflection, wavelength, EM waves sources, fluorescent, types of light, light energy, blue led, lightyear, lightning, light color, UV lights, UV led, EM waves, infrared waves, electromagnetic spectrum.


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