Find the ratio of intensities of two points P and Q on a screen in Young's double-slit experiment when waves from sources `S_1 and S_2` have path difference (i) zero and (ii) `lambda//3` respectively.

Explanation

To find the ratio of intensities of two points P and Q on a screen in Young's double-slit experiment when the waves from sources \( S_1 \) and \( S_2 \) have path differences of (i) zero and (ii) \( \frac{\lambda}{3} \), we can follow these steps:

### Step-by-Step Solution

1. **Understanding the Setup**:
In Young's double-slit experiment, we have two coherent sources \( S_1 \) and \( S_2 \) that produce waves that interfere with each other on a screen. The path difference between the waves arriving at points P and Q will determine the resulting intensity at those points.

2. **Intensity Formula**:
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