The frequency of waves: definition and the ways of calculation

A common concept in physics, waves are described as disturbances that transmit energy through matters and space. Sometimes, they are associated with mass transport, sometimes, they are not. Waves are reported, in physics, at a fixed point, and consist of oscitations or vibrations of a physical field or medium. In physics, there are known two types of waves: mechanical and electromagnetic. While mechanical waves take place in solid, physical matters, electromagnetic waves do not require a physical medium to propagate. They are formed from oscillations of electrical and magnetic fields, periodic ones, generated by particles, and thus, they can also travel through the vacuum. In this category are included radio waves, microwaves, infrared radiation, visible light, ultraviolet radiation, X-rays and gamma rays.

Velocity vs. frequency of wavelengths

Another term to describe weaves is frequency. Frequency is usually described as the number of waves passing in a certain unit of time. In wave’s case, the unit used is usually Hertz. The equation for this is one wave per one second, equals a Hertz. As wavelengths increase, the frequency decreases, thus the relationship between the two is an indirectly proportional one.

Many mix wave frequency with wave velocity. However, these two are not even remotely related. Velocity is the same as speed. In the case of many types of waves, the speed is the same for all: 186,000 miles per second. This is described as the speed of light. Frequency is not describing how fast is a wave travelling but how many complete cycles are completed in a certain time unit.

The frequencies of light waves

Now that we know what frequencies are and their relationship with waves, we have to understand the fact that depending on the light, there are various frequencies for each of those.

  • Visible light, usually referred to as colour, is between 430 trillion hertz (red) and 750 trillion hertz (violet).
  • Invisible light – the frequency varies from less than 3 billion hertz to greater than 3 billion hertz (gamma rays).

Everything in between the two above is usually referred to as the electromagnetic spectrum. The first to link the electromagnetic spectrum to electromagnetism is Michael Faraday. He observed that polarized light traveling through transparent materials responds to the magnetic field. This is known as the Faraday Effect.

How to calculate frequencies of light?

Sound, light, and water have all the same frequency and they are calculated based on the same formula. The frequency of light (f) is the number of times a wave’s crest passes a fixed point in a certain time unit, usually second (s). The speed of light is approximately 300,000 km/s and it is noted with a c, usually. The Greek symbol for lambda will represent the wavelength of the wave. You will get the frequency of the light by dividing the speed with which the wave you want to calculate, by the wavelength of the wave in the matter. While there are other formulas based on which you can calculate this, this one is the simplest.

What is gravitational lensing?

Everyone is already familiar with the real-life applications of gravity. Not only do we feel its effects every day, but also we are provided enough information from mass media. Gravity allows to keep our feet on the ground. Without gravity, we would simply float off into the atmosphere. Gravity is an essential force in the Universe, holding the Earth and all of the planets in place. Our galaxy is made up of hundreds of billions of stars and all of them hold together due to the force of attraction.

One of the most interesting things about gravity is that it operates like a lens, making distant objects appear nearer. Thanks to Albert Einstein’s insight on how gravity works, we now know that the universe isn’t static. On the contrary, it’s fully dynamic. Einstein predicted gravitational lensing, in which massive objects can bend light. Clearly, he was ahead of his time.

Cosmic lensing is something that allows us to see faint objects that otherwise would not be visible. What happens is that the light emitted from faraway galaxies goes past massive objects, such as galaxy clusters, and the force of attraction from these objects can distort or bend the light. This is the so-called gravitational lensing effect. The bigger the object is, the more powerful its gravitational pull is and, consequently, the greater the refraction of light is.

The gravitational lens effect was first validated during the first total solar eclipse in 1919 when astronomers Arthur Eddington and Frank Watson Dyson noticed that the position of the stars close to the Sun was a little bit different. The astronomical objects near the Sun were not in the correct place, the light coming from these stars being bent due to the curvature of spacetime. The two astronomers basically proved the theory of relativity. However, it was not until 1936 that humanity understood the true potential of gravitational lensing. Fritz Zwicky discovered that cosmic lensing can be used to study distant galaxies. Cosmic lensing is very similar to a magnifying glass in the sense that it makes distant objects easier to examine. It’s, therefore, possible to image the universe with the help of gravity.

The natural phenomenon can magnify light by factors of 10 and 20. What is more, the gravitational lensing effect is visible only in rare cases. The good news is that there is a telescope that can capture the phenomena. We are talking about Hubble. Hubble is capable of seeing the most remote cosmic lenses. The space telescope was launched in 2009 and since then it has offered sensitive images obtained from distant universes. At present, there is another program that guarantees to reveal galaxies a lot faster.

Most of the clusters of galaxies consist of matter that does not emit light – in other words, dark matter. Examining the nature of gravitational lensing patterns allows astrophysicists to understand how dark matter is distributed. If we understand dark matter, then we understand how background galaxies are distorted. An example in dark matter research is represented by Bullet Cluster. The nature of dark matter will be discussed another time.

The bottom line is that our Universe is full of cosmic lenses. It is these lenses that provide us useful insight into various parts of the universe. The question now is where should we concentrate our gravitational lensing efforts.