Problem 5.214

Two plates, one of thickness \(d_{1}=3.8 \mathrm{~mm}\) and the other of thickness \(d_{2}=9.0 \mathrm{~mm},\) are manufactured from a certain substance. When placed alternately in the way of monochromatic light, the first transmits \(\tau_{1}=0.84\) fraction of luminous flux and the second, \(\tau_{2}=0.70 .\) Find the coefficient of linear absorption of that substance. Light falls at right angles to the plates. The secondary reflections are to be neglected.