# Combination lens and double slit interference

A source of monochromatic light with wavelength lambda is located on optical (principal) axis on distance p from converging lens, which consist of two pieces of different glass as shown in the figure. Parallel to the lens axis screen is D away from it (D>>p). Define lens focal length f and derive the expression for estimating the order of the bright fringes that can be expected on the screen at point A.

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Every thing is similar to what we did in the earlier problem. Only difference is that the focal length f needs to be found for the combination lens.

Let f1 and f2 be the focal lengths of the two lenses with refractive indices n1 and n2 respectively.

Using Lensmaker's equation 1/f = (n-1)[1/R1 - 1/ R2]

1/f1 = (n1 - 1) [1/R - 1/r]

1/f2 = (n2 - ...

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I have provided very detailed and step by step solution to this problem along with a clearly marked diagram. Answer is in a 3-page word document.