A converging lens having a focal length F = 10 cm is cut in half, and the halves are separated by a distance a = 0.5 mm (bilens). Estimate the number of interference fringes on a screen located behind the lens at a distance D = 60 cm, if in front of the lens there is a point source of monochromatic light ( L = 5·10-5 cm) located at a distance d = 15 cm from it (Fig.).

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