When a mica sheet of thickness 7 microns and `mu=1.6` is placed in the path of one of interfering beams in the biprism expriment then the central fringe gets at the position of seventh bright fringe. What is the wavelength of light used?

Explanation

To solve the problem, we need to find the wavelength of light used when a mica sheet is placed in the path of one of the interfering beams in a biprism experiment. Here’s a step-by-step solution:

### Step 1: Understand the given data
- Thickness of the mica sheet, \( t = 7 \) microns = \( 7 \times 10^{-6} \) meters
- Refractive index of mica, \( \mu = 1.6 \)
- The central fringe shifts to the position of the 7th bright fringe, so \( n = 7 \).

### Step 2: Calculate the optical path difference
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