Problem 4 - 43 Years JEE ADVANCED (1978-2020) + JEE MAIN Chapterwise & Topicwise Solved Papers Chemistry

Question

Tyndall effect is observed when :(a) The diameter of dispersed particles is much larger than the wavelength of light used. (b) The diameter of dispersed particles is much smaller than the wavelength of light used. (c) The refractive index of dispersed phase is greater than that of the dispersion medium. (d) The diameter of dispersed particles is similar to the wavelength of light used.

Step-by-Step Solution

Answer

(d) The diameter of dispersed particles is similar to the wavelength of light used.

Step 1: Understand Tyndall Effect

The Tyndall effect refers to the scattering of light by particles in a colloid or dispersed medium. It helps differentiate between solutions and colloids by observing light passing through a sample.

Step 2: Analyze the Conditions

Evaluate each condition provided in the question. The Tyndall effect specifically occurs when the size of the dispersed particles is significant enough relative to the wavelength of light used to cause visible light scattering.

Step 3: Examine Particle Size Requirements

For the Tyndall effect to occur, the diameter of the dispersed particles must be similar or comparable to the wavelength of light used. This means that the particles are large enough to scatter visible light.

Step 4: Evaluate Each Option

Review each option: (a) Particles much larger than the wavelength of light tend to obstruct or block light rather than scatter it. (b) Particles much smaller than the wavelength of light would not scatter light appreciably. (c) The refractive index factor is unrelated to the Tyndall effect. (d) Particles of diameter similar to the wavelength of light are optimal for producing visible scattering, demonstrating the Tyndall effect.

Step 5: Conclusion

The correct condition for observing the Tyndall effect is when the diameter of the dispersed particles is similar to the wavelength of light used, which is reflected in option (d).

Key Concepts

Colloids

Colloids are mixtures where one substance is dispersed evenly throughout another. This creates a system where you have tiny particles suspended within a continuous medium. These particles are too small to settle out of the mixture due to gravity, yet large enough to scatter light.

Here are some important features of colloids:

• Particles in colloids range in size from 1 to 1000 nanometers.
• They can be found in different phases, such as solid, liquid, or gas.
• Examples include milk, fog, and whipped cream.

Colloids are essential in the study of the Tyndall effect because the effect occurs specifically in these kinds of mixtures. The dispersed particles in colloids are significant enough in size to scatter light, which distinguishes them from solutions where the solute is completely dissolved and does not scatter light.

Light Scattering

Light scattering happens when light rays are deflected from their original path after encountering particles. This phenomenon is fundamental to many optical effects in nature, including the Tyndall effect. When light passes through a colloid, the dispersed particles disrupt the incident light, causing it to scatter in different directions.

Important points about light scattering:

• It is more pronounced when the particles are similar in size to the light's wavelength.
• It's responsible for the blue color of the sky, as shorter wavelengths (like blue) are scattered more than longer wavelengths (like red).
• This is crucial for differentiating between true solutions and colloids.

In practical applications, the scattering of light can help in understanding the properties and behavior of colloids, making it a pivotal tool in various scientific fields.

Particle Size

Particle size is a critical factor in determining whether a particular light scattering effect, like the Tyndall effect, will occur. The diameter of the particles must be neither too small nor too large relative to the light's wavelength; it needs to be just right.

Here's why particle size matters:

• When particles are too small compared to the wavelength of light, they don't scatter the light effectively; the light passes through almost unaffected.
• If they are too large, they might block or absorb the light rather than scattering it.
• The ideal particle size for the Tyndall effect would be around the same length as the light's wavelength. This allows for maximum scattering and makes the phenomenon observable.

Achieving the right particle size is crucial in experiments and real-world applications where observing the Tyndall effect is necessary. It helps in material characterization and the creation of various products.

Wavelength of Light

The wavelength of light is the distance between successive peaks of a wave, typically measured in nanometers (nm) for light. This property of light plays a significant role in the Tyndall effect and relates closely to particle size within a colloid.

Key details about wavelength include:

• The visible light spectrum ranges approximately from 400 nm (violet) to 700 nm (red).
• Shorter wavelengths scatter more than longer ones — this is why the sky appears blue.
• The scattering effect and its visibility depend on how the wavelength compares to the size of the dispersed particles.

Understanding the wavelength of light is important in predicting and explaining why certain materials show the Tyndall effect. Scientists can use this principle to measure and infer characteristics of colloidal particles and even identify unknown substances.