What is light? How fast does light travel?

Light is a form of energy(an electromagnetic radiation) which enables us to see the world around us.

Light is a connection between us and the observable universe. It is considered to be the smallest amount of energy that can be transmitted.

After decades of debates it has been declared that light shows wave-particle duality.

The particle that carries light energy is called a photon. Photons are considered to be very tiny packets of energy which can't be cut down into smaller pieces but can be destryed or created.The photon was used by Einstein to demonstrate photoelectric effect for which he won nobel prize.

Light as a wave was used to demonstrate the double slit experiment.

By Light one usually means visible light which is a tiny part of visible spectrum.

Light can have various frequency and so various wavelengths as well, light waves can have wavelength of #100,000km# also. Large number right?

After centuries, physicists have been able to find the speed of light (it is also the speed of every massless particle) that is #299,792,458ms^(-1)#.

At first it was thought that light was instantaneous but later some experiments tried to find the exact speed and the belief that light was instantaneous was found incorrect.

Many physicists tried to find speed of light. One of the speed measured in early time was about #200,000ms^(-1)# which is very far away from real number but still it was a good approximation at that time. Since then other experimental values approached this value we accept now and it is the correct one.
Amazing fact: photon doesn't experience time.