Question

Assertion: A beam of white light gives a spectrum on passing through a hollow prism.
Reason: Speed of light outside the prism is different from the speed of light inside the glass prism.
A. Bothe assertion and reason are correct and reason is the correct explanation of the assertion.
B. Bothe assertion and reason are correct and reason is not the correct explanation of the assertion.
C. Assertion is correct, but reason is incorrect.
D. Assertion is incorrect, but reason is correct.
E. Both assertion and reason are incorrect.

Answer 1

A spectrum is an ordered separation of colored light rays from red to violet like the rainbow colors. White light or visible light must pass through an object like a prism to produce a spectrum. When light passes through different objects, its speed also changes.

Complete step by step answer:
We are given an assertion and a reason.
We have to find whether the assertion is true or not and the reason is true or not.
Spectrum is the dispersion of white light or visible light into its component colors when passing through objects like prisms. The obtained colors will be red, orange, yellow, blue, green, indigo and violet.
A hollow prism contains air in it, so when a beam of white light is passed through it, it does not give a spectrum. Because light is passed from air through air, so there will be no spectrum produced.
Speed of light in gases is more than the speed of light in solids. Prism is solid and outside the prism is air.
So the speed of light outside the prism is greater than the speed of light inside the glass prism. The glass prism is not hollow so the speed will be obviously changed.
Therefore, the assertion is incorrect and the reason is correct.

So, the correct answer is “Option D”.

Note:
Assertion means a statement and reason is the explanation about that particular statement. You have to find out whether each statement is correct or not. If both the statements are correct, you have to find out whether the reason supports the assertion or not. Do not confuse in answering these types of questions. White light has all the visible wavelengths whereas monochromatic light has a single wavelength. Sun, light bulbs and stars are sources of white light whereas laser light is an example of monochromatic light. Do not confuse white light with monochromatic light.