Question

In the following, for which colour speed of light in water will maximum?
A. Red
B. Yellow
C. Green
D. Violet

Answer 1

Hint: The speed of light in any medium will depend upon the refractive index of that medium. In medium, the light will not propagate with the same speed as it travels in vacuum. The speed of light in the vacuum will be $c$ .

Complete answer:
The speed of light is the speed at which the light waves travel in different mediums. The speed of the light in vacuum is denoted as $c$ and is shown below
$v = \dfrac{c}{\mu }$
Here, $c$ is the speed of light in vacuum, $v$ is the speed of light in water and $\mu $ is the refractive index of water.
The speed of light in water will depend upon the refractive index of the water. The refractive index of any material is defined as the ratio of speed of light in vacuum $c$ to the phase velocity. The refractive index of any material depends on the light’s frequency, polarization, or direction of propagation. The refractive of the transparent materials will be greater than one, which means that the phase velocity phase velocity is less than the speed of light in vacuum.
Now, the larger refractive index indicates that the speed of light is low. On the other hand, the lower refractive index indicates that the speed of light is high. Now, the speed of light in water will be the minimum for red colour. Therefore, the speed of light for red colour in water will be maximum.

Hence, option A is the correct option.

Note:Now, you might wonder why the red colour has a minimum refractive index. This is because the wavelength of the red colour is maximum. Also, we have used the term phase velocity in the question. The phase velocity is the speed at which the individual crests and troughs will propagate.