Tyndall effect is applicable when

Options

A. The diameter of the dispersed particle is not much smaller than the wavelength of the light used.
B. The diameter of the dispersed particles is much smaller than the wavelength of the light used.
C. The refractive indices of the dispersed phase and the dispersed phase and the dispersion medium must be same.
D. The refractive indices of the dispersed phase and the dispersion medium must differ greatly in magnitude.

Answer

To determine when the Tyndall effect is applicable, we need to analyze the options provided in the question. The Tyndall effect refers to the scattering of light by colloidal particles, which makes the path of the light beam visible. Here’s a step-by-step solution:

### Step 1: Understanding the Tyndall Effect
The Tyndall effect occurs when light is scattered by particles in a colloid or in very fine suspensions. This scattering makes the path of the light beam visible.

### Step 2: Analyzing the Options
1. **Option A**: The diameter of the dispersed particle is not much smaller than the wavelength of the light used.
- This statement is true. For the Tyndall effect to occur, the size of the dispersed particles should be comparable to the wavelength of the light. If the particles are too small (much smaller than the wavelength), the light will pass through without scattering.

2. **Option B**: The diameter of the dispersed particles is much smaller than the wavelength of the light used.
- This statement is false. If the particles are much smaller than the wavelength, the Tyndall effect will not be observed.

3. **Option C**: The refractive indices of the dispersed phase and the dispersion medium must be the same.
- This statement is false. If the refractive indices are the same, there will be no scattering of light, and thus the Tyndall effect will not occur.

4. **Option D**: The refractive indices of the dispersed phase and the dispersion medium must differ greatly in magnitude.
- This statement is true. A significant difference in refractive indices is necessary for the scattering of light, which is a requirement for the Tyndall effect.

### Step 3: Conclusion
Based on the analysis:
- The correct options are **Option A** and **Option D**.

### Summary of the Solution
The Tyndall effect is applicable when:
- The diameter of the dispersed particles is not much smaller than the wavelength of the light used (Option A).
- The refractive indices of the dispersed phase and the dispersion medium differ greatly in magnitude (Option D).