The velocity of light is maximum in a medium of
(A) diamond
(B) water
(C) glass
(D) vacuum
The correct answer and explanation is:
The correct answer is (D) vacuum.
The velocity of light is maximum in a vacuum. This is because, in a vacuum, there are no particles to interact with the light, and it travels at its highest speed, which is approximately 299,792,458 meters per second (or around 3 × 10^8 m/s).
When light travels through any medium other than a vacuum, such as air, water, glass, or diamond, its speed decreases. This reduction in speed occurs due to the interactions between light and the particles in the medium. Each medium has a property called the refractive index, which measures how much light slows down when passing through the material. The refractive index of a medium is calculated as the ratio of the speed of light in a vacuum to the speed of light in the medium.
The refractive index is always greater than 1 for all substances, meaning light slows down when it enters any medium. For example, the refractive index of diamond is around 2.42, meaning light travels about 2.42 times slower in diamond than in a vacuum. In water, the refractive index is around 1.33, and in glass, it is typically about 1.5. Thus, the speed of light is slower in these materials compared to its speed in a vacuum.
The slowing down of light is due to the fact that photons (the particles of light) interact with the atoms in the medium. As the photons are absorbed and re-emitted by the atoms, the light appears to travel more slowly. However, once light exits the medium and returns to a vacuum, it regains its maximum speed.
This principle is fundamental in understanding phenomena like refraction, where light bends when it enters a new medium at an angle, which is crucial in fields such as optics and telecommunications.