Question

When sunlight passes through the window of your house, the dust particles scatter the light making the path of the light visible. This phenomenon is called as:

• A. Brownian motion
• B. Tyndall effect
• C. Raman effect
• D. Uniform motion

Hint:

The Tyndall effect is responsible for the visible beams of light that can be seen when light passes through dusty air.

Answer 1

The Correct Option is B

• Option 1: Brownian motion - This is incorrect. Brownian motion refers to the random movement of colloidal particles suspended in a medium, not the scattering of light.
• Option 2: Tyndall effect - This is the correct answer. The Tyndall effect refers to the scattering of light by colloidal particles or small particles in a medium. This is what makes the path of light visible when dust particles scatter sunlight.
• Option 3: Raman effect - The Raman effect refers to the scattering of light in which there is a shift in the wavelength of light due to interactions with molecules. This is not the phenomenon described here.
• Option 4: Uniform motion - This is incorrect. Uniform motion refers to motion at a constant speed in a straight line, which does not relate to the scattering of light.

Explanation:

The phenomenon described is called the Tyndall effect. It occurs when light is scattered by small particles or colloidal particles, making the path of light visible. In the case of sunlight passing through a window, dust particles scatter the light, which is why we can see the beam of light.

Answer 2

The description in the question is entirely about light becoming visible as it travels through a group of particles, so the right term has to be about optics, not about motion. Let's check what each option is actually about.

1. Brownian motion: This describes particles jittering around randomly because molecules keep bumping into them. It says nothing about light being scattered or a beam becoming visible, so it answers a different kind of question.
2. Tyndall effect: When particles like dust are roughly the same size as the wavelength of visible light, they scatter that light strongly in many directions. Some of that scattered light reaches our eyes from along the entire path of the beam, which is why we see the beam itself rather than just where it lands. This is precisely the scattering described in the question.
3. Raman effect: This is about light changing its wavelength, and therefore its colour, at a molecular level, after interacting with molecules, which is used to study molecular vibrations. The question describes ordinary scattering that makes a light path visible, not a wavelength shift, so this does not fit.
4. Uniform motion: This is a mechanics term for something moving at constant speed in a straight line. It has no connection to light or particles scattering it at all.

Light becoming visible as a beam because dust particles scatter it in all directions is the defining feature of the Tyndall effect.

So the correct answer is Tyndall effect.