Question

How will you use two identical prisms so that a narrow beam of white light incident on one prism emerges out of the second prism as white light?
A) Just put them side by side
B) One placed on the top of the other
C) One placed inverted with respect to the other
D) None of the above

Answer 1

Hint: In this question, use the concept of the prism that the prism is a piece of glass or any transparent material which is cut and arranged in such a way that it is useful in analyzing and refracting the light. When the white light incident on the prism it splits the light into different color wavelengths.

Complete step by step answer:
In this question, there are two prisms which are to be arranged in such a way that the reflected light from one prism emerges out of the second prism as white light only.
We know that when white light is passed through the prism, it gets separated into its constituents’ colors due to the wavelengths of the different colors. The deviation of the different color rays depends on the wavelength that is the shorter the wavelength the larger is the deviation.
Now, in order to get back the white light, one must place the second prism inverted with respect to the other so that the spectrum bends with an equal amount and we get white light as a result.
Consider the following diagram of the two identical prisms to get the white light back as

We can see in the above diagram that first the white light ray falls on the prism and then the white light is diffracted into seven colors from violet(V) to red(R) as shown in the above figure. Now, to get the same white light put the identical prism in an inverted way, so as the different color rays refracted to a point to give us the white light again.

Therefore, Option (C) is the correct answer.

Note:
The prism splits the white light into seven colors that is VIBGYOR that is Violet, Indigo, Blue, Green, Yellow, Orange, and Red. The refraction of the prism depends on the refractive index of the material of the prism.