A: When a tiny circular obstacle is placed in the path of light from a distant source, a bright spot is seen at the centre of the shadow of the obstacle.
R: Waves diffracted from the edge of the circular obstacle interfere constructively at the centre of the shadow producing a bright spot.

Options

A. IF both Assertion & Reason are true and the reason is the correct explanation of the assertion, then mark (1).
B. If both Assertion & Reason are true but the reason is not the correct explanation of the assertion, then mark(2)
C. IF Assertion is true statement but Reason is false then mark(3)
D. If both Assertion and Reason are false statements, then mark (4)

Answer

To solve the problem, we need to analyze the assertion and reason provided:

**Assertion (A):** When a tiny circular obstacle is placed in the path of light from a distant source, a bright spot is seen at the center of the shadow of the obstacle.

**Reason (R):** Waves diffracted from the edge of the circular obstacle interfere constructively at the center of the shadow producing a bright spot.

### Step-by-Step Solution:

1. **Understanding Diffraction:**
- When light encounters an obstacle, it does not just travel in straight lines; instead, it bends around the edges of the obstacle. This phenomenon is known as diffraction.

**Hint:** Recall the definition of diffraction and its dependence on the size of the obstacle relative to the wavelength of light.

2. **Considering the Circular Obstacle:**
- In this scenario, we have a tiny circular obstacle placed in the path of light from a distant source. The light rays that strike the edge of the circular obstacle will diffract.

**Hint:** Visualize how light behaves when it encounters a circular edge, and think about the path of the light rays.

3. **Formation of Shadow:**
- The region behind the obstacle where light is blocked is called the shadow. However, due to diffraction, light waves bend around the edges of the obstacle.

**Hint:** Remember that the shadow is not completely devoid of light due to the diffraction effect.

4. **Interference of Light Waves:**
- The diffracted waves from the edges of the circular obstacle will spread out and overlap. At the center of the shadow, these waves can interfere with each other.

**Hint:** Consider the principle of superposition, where overlapping waves can add together constructively or destructively.

5. **Constructive Interference:**
- At the center of the shadow, the waves from the edges of the obstacle meet in phase, leading to constructive interference. This results in a bright spot at the center of the shadow.

**Hint:** Think about the conditions for constructive interference, such as the path difference being an integer multiple of the wavelength.

6. **Conclusion:**
- Both the assertion and the reason are correct. The assertion describes the observation of a bright spot at the center of the shadow, and the reason explains why this occurs due to constructive interference of diffracted waves.

**Hint:** Summarize the relationship between diffraction, interference, and the resulting bright spot.

### Final Answer:
Both the assertion (A) and the reason (R) are correct, and the reason correctly explains the assertion.