A polished glass plate is placed above a ground glass cube, the edge length of which is 2 cm, so that a thin air layer appears in the space between it and the cube. If the plate is illuminated from above at a right angle to its surface with radiation with wavelengths from 400 to 1150 nm, for which the plate is transparent, then in the reflected light the condition of maximum intensity is satisfied only for two wavelengths: l0 = 400 nm and for one more wavelength. Determine this wavelength. Calculate how much the temperature of the cube must be increased so that it touches the plate. The coefficient of linear expansion of glass is a=8•10-6 K-1, the refractive index of air is n=1. The distance from the base of the cube to the plate does not change during heating.
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