Diffraction of light is observed only, when the obstacle size is-

Options

A. should be much larger than the wavlength
B. has no relation to wavelength
C. should be of the order of wavelength
D. should be `lambda//2` where `lambda` is the wavelength

Explanation

To determine the condition under which diffraction of light is observed, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Diffraction**:
- Diffraction is the bending of light waves around obstacles or through openings. It occurs when light encounters an obstacle or a slit that is comparable in size to its wavelength.

2. **Identifying the Size of the Obstacle**:
- For diffraction to be noticeable, the size of the obstacle (or aperture) must be on the order of the wavelength of the light being used. This means that the dimensions of the obstacle should be similar to the wavelength.

3. **Comparing Sizes**:
- If the obstacle is much larger than the wavelength, diffraction effects will be minimal, and light will mostly travel in straight lines. Conversely, if the obstacle is much smaller than the wavelength, diffraction will also be negligible.

4. **Conclusion**:
- Therefore, the correct condition for observing diffraction is that the size of the obstacle must be comparable to the wavelength of light. This can be expressed as:
\[ d \approx \lambda \]
- Where \(d\) is the size of the obstacle and \(\lambda\) is the wavelength of light.

5. **Final Answer**:
- The size of the obstacle should be of the order of the wavelength of light.