Two beams of white light from one source arrive at the observation point P (Figure a) with a path difference D. Using a high-resolution spectroscope, the energy distribution in the spectrum of the vibration that occurs at point P when both beams are superimposed is studied. It turned out that alternating maxima and minima of the spectral intensity I(n) are observed, and the frequency interval between adjacent maxima is Dn = 10 MHz (Figure b). Determine the stroke difference D.

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