Waves
5 marks · NormalWhite light is passed through a glass prism in a laboratory experiment. The student notices the formation of a rainbow-like spectrum on the screen beyond the prism.
Explain why the prism produces a spectrum of colours from white light.
Put the following colours in order from longest to shortest wavelength: green, red, violet, yellow.
State whether red or violet light is refracted most by the prism and explain your answer.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
Show answer
(a) A prism separates white light into its different colours (spectrum) because each colour has a different wavelength and is refracted by a different amount. Shorter wavelengths (like violet) bend more than longer wavelengths (like red).
(b) Red, yellow, green, violet (from longest to shortest wavelength).
(c) Violet light is refracted the most because it has the shortest wavelength, so it bends more in the glass than red light (which has the longest wavelength).
Common mistakes: Mixing up wavelength order; Confusing red/violet refraction
Show mark scheme and worked solution
Marking points
B1 (a) · 1 mark · States that prism disperses/separates white light into colours/spectrum.
B2 (a) · 1 mark · Explains cause: different wavelengths are refracted different amounts.
B3 (b) · 1 mark · Correct order: red, yellow, green, violet.
B4 (c) · 1 mark · Identifies violet as most refracted (or red as least).
B5 (c) · 1 mark · Gives correct explanation (shorter wavelength bends more).
Worked solution
a) White light is a mixture of all visible colours. The prism splits the light (dispersion) because each wavelength is refracted by a different amount; shorter wavelengths (violet) bend more than longer ones (red).
b) Red, yellow, green, violet (from long to short wavelength).
c) Violet is refracted most as it has the shortest wavelength, so it slows more and bends more than red.