Question

Assertion (A) : White light is dispersed by a glass prism into seven colours.
Reason (R) : The red light bends the least while the violet the most when a beam of white light passes through a glass prism.

• A. Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).
• B. Both Assertion (A) and Reason (R) are true and Reason (R) is not the correct explanation of Assertion (A).
• C. Assertion (A) is true, but Reason (R) is false.
• D. Assertion (A) is false, but Reason (R) is true.
  {5pt}

Answer 1

The Correct Option is A

Assertion (A): When white light passes through a glass prism, it splits into its constituent spectrum of colors (typically observed as violet, indigo, blue, green, yellow, orange, red - VIBGYOR). This phenomenon is called dispersion. The assertion states it splits into seven colors, which is a common way to describe the visible spectrum. This is true. Reason (R): Different colors of light have different wavelengths. The refractive index of glass varies slightly with the wavelength of light. Violet light (shorter wavelength) has a higher refractive index in glass than red light (longer wavelength). Due to this difference in refractive index, violet light bends (deviates) more than red light when passing through a prism. Red light bends the least. This statement is true. Explanation: The reason (R) correctly explains why dispersion (Assertion A) occurs. The differential bending of different colors of light due to their different speeds (and hence refractive indices) in the prism material is the cause of white light splitting into its spectrum. \[ Both (A) and (R) are true, and (R) correctly explains (A). \]