In a biprism experiment, a slit is illuminated by a light of wavelength `4800`. The distance between the slit and biprism is and the distance between the biprism is `15cm` and the distance between the biprism and eyepiece is `85cm`. If the distance between virtual sources is `3mm`, determine the distance between `4th` bright band on one side and `4th` dark band on the other side of the central bright band.

Explanation

To solve the problem, we will follow these steps:

### Step 1: Understand the given data
- Wavelength of light, \( \lambda = 4800 \) angstroms = \( 4800 \times 10^{-10} \) m
- Distance between the slit and the biprism, \( d_1 = 15 \) cm = \( 0.15 \) m
- Distance between the biprism and the eyepiece, \( D = 85 \) cm = \( 0.85 \) m
- Distance between the virtual sources, \( d = 3 \) mm = \( 3 \times 10^{-3} \) m

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