Question

ASSERTION: Light of different colours travels at different speeds in vacuum.
REASON: Speed of light depends on medium.
A) Both the assertion and reason are correct and reason is the correct explanation for the assertion
B) Both the assertion and reason are correct and reason is NOT the correct explanation for the assertion
C) Assertion is correct but the reason is incorrect.
D) Assertion is incorrect but the reason is correct.

Answer 1

Hint: We know that white light is a combination of different colours in the spectrum. Each colour holds different properties and it possesses different wavelengths.
We also know that there is a variation in the propagation of light as it changes its medium while travelling. The angle with which the rays emerge show variation.

Complete step by step answer:
We know that light is an electromagnetic wave which travels in the form of waves. Electromagnetic waves propagate through vacuum with the same velocity, irrespective of wavelength.
Our assertion is that light of different colours travels at different speeds in vacuum. However, all forms of light travel with the same speed irrespective of wavelength. Hence, our assertion is wrong.

As light travels from one medium to another, its velocity changes as the refractive index of the material or the medium changes. In other words, the refractive index determines how fast the light can travel in a medium. Hence we can say that the speed of light is dependent on the medium. Hence our reason is correct.

To conclude, our assertion is incorrect but the reason is correct.
Option D is the correct answer among the given options.

Note:Refractive index is used to measure all the forms of matter. It is commonly used to measure the concentration of a solute in an aqueous solution. It is also used to differentiate between different types of gemstone, due to the unique chatoyance displayed by individual stones.