Name and explain the phenomenon of light due to which the path of a beam of light becomes visible when it enters a smoke filled room through a small hole. Also state the dependence of colour of the light we receive on the size of the particle of the medium through which the beam of light passes.
Name and explain the phenomenon of light due to which the path of a beam of light becomes visible when it enters a smoke filled room through a small hole. Also state the dependence of colour of the light we receive on the size of the particle of the medium through which the beam of light passes.
- Phenomenon: The phenomenon is called the Tyndall effect, which is caused by the scattering of light by minute particles (such as smoke, dust, or tiny water droplets) present in the air.
- Explanation: When a fine beam of light enters a smoke-filled room through a small hole, it collides with the suspended smoke and dust particles. These particles scatter the light in all directions, making the path of the beam visible to our eyes.
- Dependence of colour on particle size:
- Very fine particles scatter mainly light of shorter wavelengths, which is blue.
- Larger particles scatter light of longer wavelengths, such as red.
- If the size of the scattering particles is sufficiently large, the scattered light may appear white because all wavelengths are scattered almost equally.
Marking Scheme
- 11 mark
- 21 mark
- 31 mark
Hint
Think about the Tyndall effect and how the scattering of light by colloidal particles of different sizes affects the wavelength (and thus the colour) of the light that reaches our eyes.
Quick Oral Answer
The phenomenon is the Tyndall effect. It occurs because suspended particles in a colloidal solution or heterogeneous mixture scatter light in all directions, making the path of the light beam visible. The colour of the scattered light depends on the size of the particles: very fine particles scatter blue light, while larger particles scatter longer wavelengths or all wavelengths, making it appear white.
Analysis & Explanation
The Tyndall effect is a direct consequence of the scattering of light by colloidal or suspended particles in a heterogeneous mixture. The earth's atmosphere contains smoke, tiny water droplets, and dust particles. When light passes through such a medium, its path becomes visible. The color of the scattered light depends heavily on the size of the scattering particles:
- Extremely small particles (like air molecules) are highly effective at scattering shorter wavelengths (blue light).
- Larger particles (like dust and water droplets) scatter longer wavelengths (red light) or scatter all wavelengths equally, making the light appear white.
Common Mistakes
- 1Confusing scattering of light with simple refraction or reflection.
- 2Failing to mention that very large particles scatter all wavelengths equally to appear white.
- 3Not linking the visibility of the path directly to the scattering by suspended particles.
Interesting Facts
The Tyndall effect is also observed when sunlight passes through a canopy of a dense forest, where tiny water droplets in the mist scatter the light.
The blue color of the sky is due to the scattering of sunlight by nitrogen and oxygen molecules, which are much smaller than the wavelength of visible light, thereby scattering blue light more strongly than red light.
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Frequently Asked Questions
How many marks does this question carry in CBSE Class 10 Science 2024?
This question carries 3 marks in the CBSE Class 10 Science 2024 examination.
Which chapter does this question come from in Science?
This question is from the chapter "The Human Eye and the Colourful World" in the CBSE Class 10 Science syllabus.
What topic does this question cover in Science?
This question covers the topic "Scattering of Light" from CBSE Class 10 Science.
What type of question is this in the CBSE Class 10 Science 2024 paper?
This is a Short Answer question from Section C in the CBSE Class 10 Science 2024 paper.