Which of the following is correct for light diverging from a point source ?

Options

A. The intensity decreases in proporation for the distance squared.
B. The wavefront is parabolic.
C. The intensity at the wavelength does not depend on the distance.
D. None of these.

Answer

To solve the question about the behavior of light diverging from a point source, we will analyze the options provided and determine which statement is correct.

### Step-by-Step Solution:

1. **Understanding the Point Source**:
- A point source of light emits light uniformly in all directions. As the light travels away from the source, it spreads out over a larger area.

2. **Analyzing the Wavefront**:
- The wavefront created by a point source is spherical. This is because all points on the wavefront are equidistant from the source, and they have the same phase.

3. **Evaluating the Options**:
- **Option 1**: "Intensity decreases in proportional to the distance squared."
- Intensity (I) is defined as power (P) per unit area (A). For a point source, the area through which the light spreads is the surface area of a sphere, given by \(A = 4\pi r^2\).
- Thus, intensity can be expressed as:
\[ I = \frac{P}{A} = \frac{P}{4\pi r^2} \]
- This shows that intensity is inversely proportional to the square of the distance from the source, confirming that this option is correct.

- **Option 2**: "Wavefront is parabolic."
- As established, the wavefront from a point source is spherical, not parabolic. Therefore, this option is incorrect.

- **Option 3**: "Intensity at a wavelength does not depend on the distance."
- This statement is incorrect because intensity does depend on the distance from the source, as shown in the analysis of Option 1.

- **Option 4**: "None of these."
- Since we have established that Option 1 is correct, this option is also incorrect.

4. **Conclusion**:
- The correct answer is **Option 1**: "Intensity decreases in proportional to the distance squared."