Unlocking the secrets of energy: how does light travel?18th May 2023
Our world is full of wonders, and one of the most amazing ones is … light. How does light travel? What is the speed of light in water, in space, in a vacuum, how it passes through obstacles, which is faster, light or sound?
This article will answer these and other questions about this unique natural phenomenon and the main energy source for all living things.
In physical optics, light is electromagnetic wave radiation visible to the human eye. As a rule, these are waves with a length of 380 – 760 nm and a frequency of 790 – 400 THz. Also, light is often referred to as radiation outside these ranges. There are radio waves, microwaves, infrared, ultraviolet, x-ray and gamma waves but in this case, the term “light” is synonymous with the term “electromagnetic radiation”, regardless of its parameters, especially when the specification is not important, but one wants to use a shorter word. Further on, we will be discussing visible light.
You may be surprised, but our eyes capture light in the same way as a digital camera. The light flux is refracted in the crystalline eye lens (similar to the camera lens), hits the retina (matrix) and creates an impulse that the brain (processor) decodes into an image.
Where does light come from?
The entire world around us consists of atoms, which, in turn, consist of a nucleus and electrons. The nucleus is positively charged, and the electron is negatively charged, so they are attracted to each other. When heated or irradiated, the atom receives energy, which causes the electrons to go into an excited state and move away from the nucleus. However, the electron and the nucleus will still strive to get closer. When an electron returns to its ground state, it releases energy in a stream of light particles, also called photons or quanta.
What light sources are there?
Light sources are usually divided into natural and artificial ones. The brightest (both literally and figuratively) example of a natural light source is the Sun. Also, these are other stars, auroras, lightning, the bioluminescence of living organisms, the glow of oxidizing organic products and minerals, etc. Artificial sources include various types of lamps, lamps, LEDs, gas burners, and lasers.
And now, let’s find out how light travels in different environments.
As mentioned above, light is a wave, or a stream of photons called a beam. It does not require any mechanical medium, matter, or materials to propagate. This means that light can travel through a vacuum — absolutely airless space. In a homogeneous medium, the rays are straight lines. Still, when the light flux encounters an obstacle, such as an opaque object or an object with a high density, the atoms of which have many free electrons capable of absorbing photon energy in a wide range, the light is reflected from this object, absorbed by it or refracted. Whereas glass and water are transparent at these frequencies, so their atoms cannot absorb photons and, thus, transmit light.
Space is a very rarefied medium, close to vacuum, so the light of the Sun and other stars reaches us at a tremendous speed called the speed of light. It is equal to 299,792,458 m/s. To understand how fast it is, it is enough to answer the question of how long does it take light to travel from Mars to Earth? A little over three minutes. In other words, if our spaceships could travel at the speed of light, we would be to reach Mars faster than a cafe on the next block.
But even in space, there are obstacles to light. A good example of this is a solar or lunar eclipse. In the first case, the Moon is in the path of the Sun’s rays flying to the Earth, so for a moment, it obscures the star from us; in the second case, the Earth becomes an obstacle between the Moon and the Sun, preventing the Moon from reflecting the star’s light.
How fast does light travel in water?
Water is an “optically” denser medium than air, so light propagates in it not only more slowly but also with a higher refractive index. In other words, when light passes from one transparent medium to another, it is refracted at the boundary of these two media. So, how fast does light travel through water? In water, the refractive index is about 1.3, so the speed of light is reduced to 230,769 kilometres per second. Refraction can make things appear closer than they actually are. This is why, for example, a 13-foot pool appears to be only 10 feet deep.
Why does light travel faster than sound?
To answer this question, let’s recall what type of wave light is. Light is an electromagnetic wave that does not need a medium to in which to propagate. But sound is a pressure wave that definitely needs a physical medium. It is because of the interaction with the physical medium that the sound waves arise, and the denser this medium is, the faster the sound propagates. In the air, it moves at a speed of 330 meters per second; in water — 1450 meters per second; and in solid materials — up to 6000 m/s. But the sound is slower than light by about a million times, which is why we first see the lightning, and later hear the thunder. In a vacuum, sound cannot exist because there is no matter there. By the way, read this article of ours if you want to know more — Can We Hear The Sounds Of Space.
So, how does light travel? Faster than sound, rockets, and anything else known to us. In space, it feels like a fish in water, but still, it is not omnipotent, so it cannot overcome every obstacle. Seems unbelievable? Think about this when seeing a bizarre shadow or watching a solar eclipse.