Light (wavelength, frequency, photon)

What is light? Two main theories have been developed: the English mathematician and physicist Sir Isaac Newton described light as an emission of particles, and the Dutch astronomer, mathematician, and physicist Christiaan Huygens developed the theory that light travels by a wave motion. It is now believed that these two theories are essentially complementary. In fact, depending on the experimental conditions, light can act like a series of particles or like a wave.
Therefore, light can be seen in two ways:

• as a wave that travels at a certain constant velocity (the speed of light). The wave vibrates at right angles to the direction of propagation of the wave (this means that light can be polarized in two mutually perpendicular planes ):
 Where is the wavelength, the distance between two crests. The frequency ( or f ) tells how many crests pass during each time interval Light is unique among waves, since it doesn't need a medium to propagate: it can travel in vacuum, while sound cannot. Furthermore, the speed of light is the ultimate speed limit: nothing in our Universe can travel faster.
• as a bunch of particles called photons characterized by an energy E, a wavelength and a frequency ( or f ), and a speed c. These quantities are related in the following ways:
 where c is the speed of light () and h is a constant called Planck's constant.

From this formula, we know that the higher the frequency of light, the shorter its wavelength and the higher its energy. X-rays or gamma-rays are examples of high frequency and high energy light. On the other hand, Radio waves are examples of light with a long wavelength, low frequency, and low energy.