Speed of Light: Definition, Equation, Constant, Facts
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Speed of Light
Speed of Light: Since ancient times scholars, and researchers have struggled hard to study the concept of speed of light. The speed of light is defined as the speed at which electromagnetic radiation travels through space. Along with its properties of light they have also sought to study how fast light can travel through speed. In so doing, they have gained a better understanding of the concept of light’s mechanics and its role in physics, astronomy, and cosmology.
What is the Speed of Light?
The speed of light in a vacuum is a fundamental universal constant, commonly denoted by ‘c’. The value of the speed of light is exactly equal to 299,792,458 meters per second, which is approximately equal to 3×10^8 m/s. According to Einstein's theory of relativity, the speed of light is fastest than anything in the universe.
How is the Speed of Light Measured?
Until the 17th century, scholars were doubtful whether light traveled at a finite speed or instantaneously, even this was supported by the experiment that there is no time lag in the position of the earth's shadow on the moon. But Galileo doubted the speed of light as infinite and he devised an experiment of covering and uncovering lanterns, but no result was there. Thereafter, a number of attempts have been made to measure the speed of light.
| Year | Author | The method used for measuring | Speed of Light |
| 1676 | Olaus Roemer | Based upon Earth-Sun-Jupiter Geometry he devised that there would be a difference of 1000 seconds between projected time and actual time | c = 214000km/s |
| 1728 | James Bradley | By Stellar Abberation | c = 301,000km/s |
| 1849 | Armand Fizeau | First, who didn't use celestial events ( By toothed Wheel) | c = 315,000km/s |
| 1862 | Leon Foucault | By Rotating Mirror | c = 298000km/s |
| 1879 | Albert Michelson | By Rotating Mirror | c = 299910 km/s |
| 1907 | Rosa & Dorsay | By use of Maxwell's theory of Electromagnetism | c = 299788 km/s |
| 1958 | Froome | Microwave interferometer & Kerr Cell structure | c = 299,792.5km/s |
| 1983 | Adopted Value | c = 299,792. 458km/s |
Speed of Light in Different Medium
As we know, light travels at maximum speed in a vacuum and at different speeds in a different mediums. Below is the list of the mediums and their speed of light.
| Speed of Light in Different Medium | |
| Medium | Speed of Light(m/s) |
| Air | 3 x 10^8 |
| Diamond | 1.25 x 10^8 |
| Glass | 2 x 10^8 |
| Water | 2.25 x 10^8 |