Throughout our lives, we are surrounded by amazing things, objects, places. We see them, but not at all because they exist, but because of the light.
If it were not for light, then living beings would not have vision as an instrument, and we would have to be content with other senses. Like moles living underground, they are content with hearing. What is light? What is this concept from the point of view of physics and what is its significance for life on Earth?
What is light?
People have been trying to uncover the mystery of the light for many centuries, but it was only in the 18th century that it was possible to get closer to the solution. First, the Danish physicist Hans Oersteda found out that an electric current can influence the needle in a magnetic compass, and then the British mathematician James Maxwell was able to prove that magnetic and electric fields exist in the form of waves propagating at the speed of light.
From this, scientists have defined light as a form of electromagnetic radiation that is perceived by the human eye.
What is the nature of light?
Optical phenomena, which optics are studying, help to establish the nature of light. This science became one of the first branches of physics to establish the dual nature of light. According to the corpuscular theory, light is a stream of particles called photons and quanta.
According to the wave theory, light is a combination of electromagnetic waves, while optical effects occurring in nature are the result of the addition of these waves. Interestingly, both the theory of particle fluxes and the theory of waves have the right to exist.
What characteristics does light have?
Like any natural phenomenon, light has many unique characteristics, among which color is one of the most important. The electromagnetic radiation perceived by our eyes differs in the range of wavelengths and frequencies, which, in turn, affects the light spectral composition. For example, violet is seen at a wavelength of 380–440 nm and a frequency of 790–680 THz, and yellow at 565–590 nm and 530–510 THz.
In addition to color, light has the ability to move in space, refract and reflect. Refraction of light is a change in the direction of electromagnetic waves. In our everyday life, such a phenomenon is found everywhere. For example, if you look at a glass of tea with a spoon in it, you will notice that it is “refracted” at the interface between air and liquid.
Similarly, a familiar phenomenon for us is the reflection of light, which allows us to see ourselves in the water surface, in a mirror or on shiny objects. Other characteristics include the ability of light to polarize and change intensity.
What is the speed of light?
The speed of light is calculated in two substances – in a vacuum and in a transparent medium. In the first case, its indicators are unchanged. In outer space, the speed of light is a fundamental constant unit and is 299,792,458 meters per second.
It is believed that in addition to light, electromagnetic radiation (for example, X-rays or radio waves) and, possibly, gravitational waves propagate in nature at a similar speed. The speed of light in a transparent medium can vary depending on the phase of the oscillatory motion.
In this regard, a phase velocity is distinguished, which is usually (but not necessarily) less than the velocity in vacuum, and the group velocity is always less than the velocity in vacuum.
How is light perceived by the eye?
As mentioned above, the ability of a person to see surrounding objects exists only thanks to light. At the same time, we would not be able to perceive electromagnetic radiation if there were no special receptors in our eyes that react to this radiation. The human retina consists of two types of cells – rods and cones. The former are highly sensitive to light, so they can only work in low light, that is, they are responsible for night vision. However, they show the world exclusively in black and white.
The cones are less sensitive to light and provide daytime vision that allows you to see a color image. The spectral composition of light is well perceived due to the fact that in our eyes there are 3 types of cones, which differ in the distribution of sensitivity.