Question

Assertion : If a plane glass slab is placed on the letters of different colours all the letters appear to be raised up to the same height.

Reason : Different colours have different wavelengths.

A. If both assertion and reason are true and the reason is the correct explanation of the assertion.
B. If both assertion and reason are true but reason is not the correct explanation of the assertion.
C. If assertion is true but reason is false.
D. If the assertion and reason both are false.
E. If assertion is false but reason is true.

Answer 1

The assertion is true because refraction in a glass slab makes the letters appear uniformly raised, whereas the reason is true regarding the dispersion in a prism, but it is not the correct explanation for the assertion.

Step-by-step explanation:

The assertion that all letters appear to be raised up to the same height when a plane glass slab is placed over them is true, because a glass slab causes a uniform change in the path of light due to refraction, which makes the letters appear at the same height. However, the reason given that different colors have different wavelengths is true but not the correct explanation for the assertion. The reason is concerning the dispersion of light where different wavelengths are refracted by different amounts resulting in separation of colors, as in a prism, which is a different phenomenon from the uniform refraction that occurs in a glass slab.

When a plane glass slab is placed on printed letters, the light rays emanating from those letters are refracted, or bent, as they enter and exit the slab due to its different refractive index compared to the air. However, all colors are refracted uniformly (unless the medium is dispersive like a prism), and thus, the letters appear to be elevated by the same amount regardless of their color. Therefore, the reason does not correctly explain the assertion.