When white light is passed through a glass prism, a band of colours is observed on a screen placed on the other side. (i) Name this band and the phenomenon responsible for its formation. (ii) Explain why different colours emerge at different angles from the prism, and identify which colour undergoes the maximum and minimum deviation.
Generated by claude-sonnet-4-6 · 2026-06-26 01:08 · grounding rag
Model Answer
(i) The band of colours formed on the screen is called the spectrum. The phenomenon responsible for its formation is dispersion of light.
(ii) White light is made up of seven colours, each having a different wavelength. When light enters the prism, different colours bend (refract) by different amounts because each colour travels at a different speed in glass. Violet light undergoes maximum deviation (bends the most), while red light undergoes minimum deviation (bends the least). Thus, each colour emerges at a different angle, forming the spectrum — VIBGYOR.
Source: Chapter 10, Section 10.4 – Dispersion of White Light by a Glass Prism
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Explanation
- Key terms to use: spectrum, dispersion, deviation — examiners look for these exact words.
- The reason for different bending is that different colours have different speeds (and hence different refractive indices) in glass — mention this for full marks.
- Always state both: violet = maximum deviation, red = minimum deviation. Forgetting one costs a mark.
- VIBGYOR is a helpful sequence to mention briefly; it shows you know the order of colours.