If a broad source is used in interference experiment choose the incorrect statement

Options

A. a broad source is equivalent to a large number of narrow sources lying side by side
B. each set these sources produce it.s own interference pattern which may overlap and cause general illumination
C. intensity of bright fringes increases and they become broad
D. bright and dark fringes will disappear

Answer

To solve the question regarding the interference experiment using a broad source, we need to analyze the statements provided and identify the incorrect one. Here's a step-by-step breakdown:

### Step 1: Understanding the Concept of a Broad Source
A broad source in an interference experiment can be thought of as a collection of many narrow sources that are closely spaced together. This means that instead of having a single coherent source of light, we have multiple sources that can produce overlapping interference patterns.

**Hint:** Remember that a broad source can be considered as many narrow sources working together.

### Step 2: Evaluating the Statements
Now, let's evaluate the statements one by one:

1. **Statement 1:** "A broad source is equivalent to a large number of narrow sources lying side by side."
- This statement is true. A broad source indeed acts like multiple narrow sources.

2. **Statement 2:** "Each set of these sources produces its own interference pattern which may overlap and cause general illumination."
- This statement is also true. Each narrow source can create its own interference pattern, and when combined, they can lead to overlapping patterns that result in general illumination.

3. **Statement 3:** "The intensity of bright fringes increases and they become broad."
- This statement is incorrect. In a broad source, the individual bright fringes do not increase in intensity; rather, they tend to merge and become less distinct due to overlapping patterns. The bright and dark fringes may disappear because of this merging.

4. **Statement 4:** "Bright and dark fringes will disappear."
- This statement is true. As the patterns from the broad source overlap, the distinct bright and dark fringes can indeed disappear.

### Step 3: Identifying the Incorrect Statement
From our evaluation, the incorrect statement is:
- **"The intensity of bright fringes increases and they become broad."**

### Final Conclusion
The incorrect statement regarding the use of a broad source in an interference experiment is that the intensity of bright fringes increases and they become broad.