Question

The velocity of light in vacuum is:
(A). $3 \times {10^8}{\text{ m}}{{\text{s}}^{ - 1}}$
(B). $5 \times {10^8}{\text{ m}}{{\text{s}}^{ - 1}}$
(C). $3 \times {10^5}{\text{ m}}{{\text{s}}^{ - 1}}$
(D). $6 \times {10^8}{\text{ m}}{{\text{s}}^{ - 1}}$

Answer 1

Hint: In order to find the velocity of light in vacuum we will simply use the definition of speed of light and how it was measured by scientists. We will take care of the unit especially in solving such questions.

Complete step-by-step answer:
Light speed: speed at which the light waves move through various materials. In particular, the value for the speed of light in a vacuum is now defined as exactly 299,792,458 meters per second.
It all started in the 17th century by O Roemer , he observed the eclipses of Jupiter’s moon in order to find the speed of light by assuming some time difference in observations made on Earth. He obtained the value as 214,000 km/s.
Then in the 18th century James Bradley made another estimate by observing stellar aberration and obtained the value as 301,000 km/s.
Many more scientists contributed to the same through various other experiments . Finally in 1983 the value adopted was 299,792.458 km/s or 299,792,458 m/s.

The speed of light is called a natural universal constant. Its significance in describing a property of electromagnetic waves is far broader than its role. This functions as the universe 's main limiting velocity, providing an upper bound to the speed of signal propagation and the velocities of all material particles. In the renowned equation of relativity, $E = m{c^2}$Light speed (c) serves as a constant of proportionality, integrating the historically separate concepts of mass (m) and energy (E).
Hence the speed of light is equal to $3 \times {10^8}{\text{ m}}{{\text{s}}^{ - 1}}$
So, the correct answer is option A.

Note:Speed of light in vacuum is a universal constant and students must remember the value of speed of light in order to solve various questions. When the light travels from the rarer medium to denser medium say air to water, the speed of light decreases and when it moves from denser medium to rarer medium the speed of light increases.