Tyndall Effect and Scattering of Light - UNSOLVED PRACTICE SET

Q7. Define the Tyndall effect. Give two real-life Indian examples where it can be observed

Q8. Why does the sky appear blue during the day? Explain using the concept of scattering and the wavelength of blue light

Q9. Why does the sky appear reddish-orange at sunrise and sunset? Explain in terms of the path length of sunlight through the atmosphere.

Q10. State the relationship between the scattering of light and the wavelength of light. Which colour scatters the most and which scatters the least?

Q11. Explain why clouds appear white even though the sky appears blue. What does this tell you about the size of water droplets in clouds versus gas molecules in the atmosphere?

Q12. Why are traffic danger signals and the tail-lights of vehicles and aeroplanes always red or orange and never blue or violet?

Q13. Explain the Tyndall effect and its role in explaining the blue colour of the sky. Your answer must include:
(a) what the Tyndall effect is and what types of particles cause it,
(b) how the gas molecules of the atmosphere act as scatterers,
(c) the inverse fourth-power relationship between scattering intensity and wavelength — which colours scatter most and least,
(d) why we see scattered blue light when we look at the sky (not at the Sun directly), and
(e) why the sky on the Moon is black even during the day (connect to absence of atmosphere).

Q14. Explain why the Sun appears white at noon but red/orange at sunrise and sunset in India. Your answer must cover:
(a) the path length of sunlight through the atmosphere at noon vs near the horizon,
(b) which colours are scattered away at each time of day,
(c) which colours remain to reach the observer's eye at noon vs sunset,
(d) why the sky around the setting Sun is often orange and red during a beautiful Indian sunset, and
(e) why a thick layer of pollution or dust (as seen in Delhi in winter) makes sunsets even more dramatic and red.

Q15. Analyse the following observations using Tyndall effect and scattering:
(a) A beam of sunlight entering a dusty room through a window is visible as a bright shaft — explain.
(b) Milk appears white because it contains tiny fat globules that scatter all wavelengths equally — explain why equal scattering of all colours gives white.
(c) The sky near the horizon during the day appears a paler, lighter blue than overhead — explain using path length of scattered light.
(d) Fog appears white while the sky is blue — compare the size of fog droplets vs air molecules.
(e) In Indian temples, incense smoke (agarbatti) appears blue-grey from the side but reddish from the front — explain this using scattering and transmission of light.

Q16. Rayleigh's law states that the intensity of scattered light I ∝ 1/λ⁴. The wavelength of blue light is 450 nm and red light is 700 nm.
(a) Calculate the ratio of scattering intensity for blue vs red light: I_blue/I_red = (λ_red/λ_blue)⁴.
(b) How many times more is blue light scattered compared to red?
(c) This is why the sky is blue. In 2–3 sentences, explain how this ratio explains the blue sky and red sunsets.

Q17. During a winter morning in Delhi, the city is covered by a thick smog layer. The smog contains suspended particles of varying sizes.
(a) Larger particles scatter all wavelengths equally — what colour does smog appear?
(b) Tiny nanoparticles in smog preferentially scatter shorter wavelengths. As sunlight passes through 30 km of smog (compared to 10 km of clear atmosphere at noon), qualitatively describe what colours are preferentially scattered away and what colour light reaches an observer.
(c) A photographer in Delhi notices that fog-filter photos appear warmer (more orange/red) in the morning. Explain this observation using scattering.

Q18. A student shines a laser pointer (red, λ = 650 nm) and a blue LED (λ = 450 nm) through a jar of dilute milk solution (a colloid demonstrating Tyndall effect).
(a) Which beam will show a more visible Tyndall cone (be scattered more)? Justify using Rayleigh's law.
 (b) Calculate the relative scattering: (650/450)⁴.
(c) The student then shines the blue light through the solution and observes the transmitted light from the far end of the jar — what colour does it appear? Explain why.
(d) A similar experiment is what causes sunlight to turn red by sunset — connect the jar experiment to the atmosphere.