Question

Consider two equivalent, triangular hollow prisms A and B made of thin glass plates and arranged with negligible spacing as shown in the figure. A beam of white light is incident on prism A from the left. Given that the refractive index of water is inversely related to temperature, the beam to the right of prism B would NOT appear white if :

• A. both prisms are filled with hot water $\left({70}^{\circ }C\right)$
• B. both prisms are filled with cold water $\left(7^{\circ }C\right)$
• C. both prisms are empty
• D. prism A is filled with hot water $\left({70}^{\circ }C\right)$ and prism B with cold water $\left(7^{\circ }C\right)$

Answer 1

Answer: (D)

prism A is filled with hot water $\left({70}^{\circ }C\right)$ and prism B with cold water $\left(7^{\circ }C\right)$

White light will appear as white light if refractive index of both prism parts are same, as the effects of dispersion will be cancelled out. Since refractive index of both parts will not be same when parts are filled with water at different temperatures, hence white light will not come out as white light.