What is the Speed of Light?
The speed at which the light wave propagates through different materials is known as the speed of light. So, the speed of light will vary depending on the medium it propagates. In particular, the speed of light in vacuum is about 299,792,458 metres per second. When comparing the speed of light in vacuum with the speed of light in air, the speed of light in air is 1.0003 times slower than the speed of light in a vacuum. Usually, the speed of light is considered constant in nature. The constant value of the speed of light is about 3*108 m/s. This article describes the speed of light formula, equation and facts of the speed of light, and all other details are given here.
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The above image shows the values of speed of light per second, speed of light in vacuum, speed of light in km
The common terms used to measure the lights include frequency, wavelength, phase and intensity.
Frequency: The number of waves that crosses a particular point in the unit time is known as frequency. The frequency of the light refers to the colour of the light. It ranges from 430 trillion hertz to 750 trillion hertz.
Wavelength: The distance between two successive crests/ troughs of a light wave is known as wavelength. Here if the wavelength of light increases, then the frequency of light get decreases.
Intensity: The rate of emission of light from the source per unit area is called the intensity of light. The intensity of light is usually measured in Watts.
Polarization: Usually, the light wave will vibrate in all directions perpendicular to the propagation of light. If the light waves get vibrate in certain directions, then the light is called polarized light.
Properties of Light
Light has seven basic properties. They are listed below.
Reflection of Light
Refraction of Light
Dispersion of Light
Diffraction of light
Interference of light
Polarization of light
Scattering of light
The speed of light is always considered constant in nature. But it may vary for the property of electromagnetic waves. The light can serve as a single velocity throughout the universe. They don’t have any upper bound to the propagation speed of signals and for the speed of all material particles.
Relativity Equation
According to Einstein’s relativity equation, the energy of the signal (E) is equal to the product of mass and square of the speed of light (c).
E = mc2
Here, the energy of an object in rest mass is considered as m. And the speed of the object is considered as v. so, Einstein’s relativity equation is given by γm0c2.
Where, =\[\gamma = \frac{1}{\sqrt{1-\frac{\nu ^{2}}{c^{2}}}}\] represents the Lorentz factor.
Here,
m0 represents the moving particle of rest mass.
v represents the velocity.
c represents the speed of the light in a vacuum (3*108 m/s).
In the above equation, if v is zero then γ is equal to one. So, Einstein’s relativity equation, E = mc2. If the Lorentz factor γ reaches infinity, then v approaches c and it takes an infinite amount of energy to accelerate an object with mass to the speed of light. In general, no signal or energy can travel faster than the speed of light. If any object or particle that travels faster than c relative to an inertial frame of reference, then the particle or object would experience backward time travel with respect to another frame. Such a violation of causality has never been recorded and it would lead to paradoxes such as the tachyonic antitelephone.
Velocity of Light
The velocity of the light value can be calculated with the frequency and wavelength of the electromagnetic waves.
Speed of light formula
c = 𝛌f.
Here,
c represents the speed of light, the exact value of speed of light is 299 792 458 m s-1
In approximate,
The speed of light per second is equal to 3.0 x 108 m/s. The speed of light in km is equal to 300,000 km/sec.
𝛌 represents the wavelength of the electromagnetic wave
f represents the frequency of the light wave, which passes through.
As the speed of light is constant. If the wavelength of the wave increases, then the frequency of the wave will decrease accordingly.
Propagation of Light
According to classic physics, the lights are the type of electromagnetic waves. The classical behaviour of the electromagnetic waves are described in Maxwell’s equation. Here, the speed of light c in a vacuum is related to the distributed capacitance and inductance of the vacuum. They can also be represented with the electric constant ε0 and the magnetic constant μ0.
c = \[\frac{1}{\sqrt{\varepsilon _{0}\mu _{0}}}\]
In modern quantum physics, the theory of quantum electrodynamics (QED) describes the electromagnetic field. According to quantum electrodynamics, as photons are massless particles, they can travel at the speed of light in a vacuum and follow special relativity.
Speed of Light In Medium
Usually, the light cannot travel at the speed c in a medium. Here, the different types of light waves will travel at different speeds. The speed of the individual wave in a plane is considered as phase velocity vp. The largest part of the pulse travels at the group velocity Vg. The front velocity of the wave is represented as Vf.
Here, the phase velocity of the light wave is important to determine the direction the wave travels from one material to another. The phase velocity is also represented in terms of a refractive index. The refractive index of a material is defined as the ratio of light c and the phase velocity vp. The refraction index of a material also depends on the frequency, polarization, intensity or direction of propagation of the light. The refractive index of air is 1.0003 and the index of refraction denser media like water, glass and diamond are around 1.3, 1.5 and 2.4, respectively. The effective speed of light in exotic materials like Bose-Einstein condensates are only a few metres per second. Because of the occurrence of the absorption and re-radiation delay of light between atoms.
The refractive index of the transparent materials is always greater than 1, whose phase velocity is less than the speed of light c. In some cases, the refraction index will become smaller than 1 for some frequencies. The refraction index may also become negative for some exotic materials
This article described the equation and facts of speed of light. Also gave complete information about the relativity equation, propagation of light with formula and velocity of light value in detail.
FAQs on Speed of Light
1. How Does the Speed of Light Become Evident?
The speed of light seems infinite. But the true finiteness of its speed is evident in satellite communications, particularly when we use geostationary satellites.
These satellites orbit about 36,000 kilometres (km) above the Earth’s surface. The propagation delay is noticeable with the increased latency when satellite Internet services are used.
Electromagnetic waves, such as visible light, take approximately 1.3 s to cover the distance between the Earth and the moon, which is about eight minutes (8 min) to reach the Earth from the Sun.
The EM waves from stars in a Milkyway galaxy may take up to thousands of years to reach us; the EM waves from the most distant objects in the Cosmos have spent billions of years on their way to reach us, where one billion equals 1,000,000,000 or 109years.
2. How Much Part of the Visible Light Constitutes the Electromagnetic Spectrum?
Scientists estimate that the visible light spectrum makes up a small portion, i.e., 0.0035 percent of the electromagnetic spectrum.
The light that reaches our eyes constitutes less than 1% of the visible spectrum. Since the human eye is limited in its range, we can see only a small fraction of the electromagnetic spectrum. The lights that are visible are violet, indigo, blue, green, yellow, orange, and red.
3. How fast is the speed of light per hour?
Usually, the speed of light is constant. The light can travel about 1,079,252,848.8 (1.07 billion) km per hour. That is equal to 299,792,458 m/s, or about 670,616,629 mph (miles per hour).
4. What is the speed of light on Earth?
The speed of light will vary from vacuum to the presence of air. The speed of light in air is 1.0003 times slower than the speed of light in a vacuum. So, the speed of light in a vacuum is about 186,282 miles per second (299,792 kilometres per second).
5. Can an object travel at the speed of light? Why or why not?
In the universe, only massless particles like light, which is made of photons, can travel at 300,000 kilometres per second (186,000 miles per second). No other particles in the universe can travel faster than the speed of light. Because all other particles require an infinite amount of energy to accelerate the speed of the particles up to the speed of light. So, it remains impossible.
