A narrow beam of electrons passes immediately over the surface of a metallic mirror with a diffraction grating with period d = 2.0μm inscribed on it. The electrons move with velocity v, comparable to c, at right angles to the lines of the grating. The trajectory of the electrons can be seen in the form of a strip, whose coloring depends on the observation angle θ (Fig. 5.38). Interpret this phenomenon. Find the wavelength of the radiation observed at an angle θ = 45o.

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