Two parallel beams of light P and Q are incident normally on a prism and the transmitted rays are brought to focus with the help of a convergent lens as shown in Fig. 2.23. If the intensities of the upper and lower beams immediately after transmission from face AC are 4I abd I, respectively, find the resultant intensity at the focus.

Explanation

To solve the problem, we need to find the resultant intensity at the focus after two beams of light with different intensities pass through a prism and are focused by a lens. Let's break down the solution step by step.

### Step 1: Identify the intensities of the beams
The problem states that the intensities of the upper and lower beams immediately after transmission from face AC are:
- Intensity of beam P (upper beam), \( I_1 = 4I \)
- Intensity of beam Q (lower beam), \( I_2 = I \)

### Step 2: Use the formula for resultant intensity
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