Dispersion of Light through a Prism - UNSOLVED PRACTICE SET

Q7. What is dispersion of light? Why does it occur in a glass prism but NOT in a glass slab?

Q8. Write the order of colours in the visible spectrum (VIBGYOR). Which colour has the longest wavelength and which has the shortest?

Q9. Explain why violet light bends more than red light in a glass prism. Use the concepts of refractive index and speed of light.

Q10. Newton performed an experiment with two prisms — one to split white light and another to recombine the spectrum. What conclusion did he draw from this experiment?

Q11. Why does a glass prism produce a spectrum but a window pane (glass slab) does not, even though both are made of glass?

Q12. Name three phenomena in nature or daily Indian life where dispersion of light is observed. Briefly explain one.

Q13. Explain the phenomenon of dispersion of light through a glass prism in detail. Your answer must cover:
(a) what happens when white light enters the prism (refraction at the first surface),
(b) why different colours bend by different amounts (different refractive indices for different wavelengths),
(c) the order of colours in the spectrum (VIBGYOR) and which colour bends most and least,
(d) what happens at the second surface of the prism, and
(e) how Newton proved that white light is a mixture of all colours using a second inverted prism.

Q14. A glass prism has refractive indices: n_violet = 1.532, n_red = 1.515. A ray of white light enters the prism.
(a) Which colour travels slower inside the glass?
(b) Using Snell's Law, explain qualitatively why violet bends more than red.
(c) The angular spread between red and violet at the exit face is called the angle of dispersion. If n_violet gives angle of deviation 48.2° and n_red gives 46.0°, what is the angle of dispersion?
(d) What is the mean deviation (approximately) of yellow light?
(e) How does the angle of the prism (apex angle) affect the dispersion?

Q15. Compare the dispersion of white light in a glass prism and in a glass slab. Your answer must explain:
(a) why a prism produces dispersion (non-parallel faces cause different net deviations for different colours),
(b) why a glass slab does NOT produce visible dispersion (parallel faces cause the colours to recombine upon exit),
(c) describe Newton's prism experiment with diagrams or description,
(d) explain what 'recombination' of colours means and how it produces white light, and
(e) give three real-life applications or phenomena that involve the dispersion of white light.

Q16. A glass prism has a refractive index of 1.55 for violet light and 1.52 for red light.
(a) Which colour has a higher speed inside the glass? Calculate the speed of each. (c = 3 × 10⁸ m/s.)
(b) A ray of white light hits the first surface at 40°. Using Snell's Law (n₁ sin i = n₂ sin r), find the angle of refraction for violet and red separately. (sin 40° = 0.643)
(c) What is the angular separation between the two refracted rays at the first surface?

Q17. In Newton's recombination experiment, the spectrum from a prism is passed through an inverted prism of the same material and apex angle.
(a) What is observed on the screen? Explain why.
(b) If the first prism deviates violet by 48° and red by 45°, and the second prism produces equal and opposite deviations, what is the net deviation for each colour?
(c) What does this tell us about the nature of white light?
(d) If one colour is blocked (say green), what colour would be seen on the screen after recombination?

Q18. The refractive index of a glass prism for different colours of light can be estimated from the minimum deviation formula. For a prism with apex angle A = 60°, the minimum deviations are δ_red = 38° and δ_violet = 40°.
(a) Using n = sin[(A + δ)/2] / sin(A/2), calculate n_red and n_violet. (sin 49° ≈ 0.755, sin 50° ≈ 0.766, sin 30° = 0.5.)
(b) Which colour has the higher refractive index?
(c) What does this confirm about the speed of each colour in glass?