The Human Eye and the Colourful WorldPractice Questions & MCQs

Q1. Consider the following statements about dispersion: (I) Violet is deviated the most by a prism. (II) White light is a mixture of seven colours. (III) Red has the shortest wavelength. Which of the above statement(s) is/are correct?

• A.Only I
• B.Only I and II
• C.Only III
• D.None of these

Answer: B. Only I and II

Which principle settles this? Correct: I, II. Does that line up with one of the options? Yes - Correct. And the rest? option A) 'Only I' fails since Re-check each statement individually; option C) 'Only III' doesn't hold - Re-check each statement individually. Pick: B) Only I and II.

Q2. Light from a projector lamp crosses a prism, deviating red 38 degrees and violet 42 degrees; by how many degrees is the violet ray spread away from the red ray?

• A.4 degrees
• B.38 degrees
• C.40 degrees
• D.80 degrees

Answer: A. 4 degrees

Angular dispersion = deviation of violet - deviation of red = 42 - 38 = 4 degrees. Violet is always bent more than red, so the difference gives the spread of the spectrum.

Q3. A lighthouse-glass prism separates a beam, turning red 36 degrees and violet 40 degrees; what is the angular dispersion of this prism for the red-violet pair?

• A.4 degrees
• B.36 degrees
• C.76 degrees
• D.38 degrees

Answer: A. 4 degrees

Angular dispersion = deviation of violet - deviation of red = 40 - 36 = 4 degrees. Violet is always bent more than red, so the difference gives the spread of the spectrum.