Problem 5.69

In Lloyd's mirror experiment (Fig. 5.13) a light wave emitted directly by the source $S$ (narrow slit) interferes with the wave reflected from a mirror $M .$ As a result, an interference fringe pattern is formed on the screen $S c$. The source and the mirror are separated by a distance $l=100 \mathrm{~cm} .$ At a certain position of the source the fringe width on the screen was equal to $\Delta x=0.25 \mathrm{~mm},$ and after the source was moved away from the mirror plane by $\Delta h=0.60 \mathrm{~mm},$ the fringe width decreased $\eta=1.5$ times. Find the wavelength of light.