Question

A 5.3-cm-thick layer of oil (n=1.46) is sandwiched between a 1.5-cm-thick sheet of glass and a 2.3-cm-thick sheet of polystyrene plastic (n=1.59). How long (in ns) does it take light incident perpendicular to the glass to pass through this 9.1-cm-thick sandwich? Express your answer using two significant figures.

t = ___ns

Answer 1

time taken is t = t1+ t2 + t3

t1 is the time taken to travel through oil = thickness of oil / speed of light in oil = (5.3*10^-2) / ((3*10^8)/1.46)

t1 = 0.257*10^-9 sec

t2 is the time taken through thick sheet of glass

refractive index of glass is 1.5

t2 = thickness of glass / speed of light in glass = (1.5*10^-2)/((3*10^8)/(1.5)) = 0.075*10^-9 sec

t3 is the time taken through plastic

t3 = thickness of plastic/ speed of light in glass = (2.3*10^-2)/((3*10^8)/(1.59)) = 0.1219*10^-9 sec

t = t1+ t2+ t3

t = (0.257+0.075+0.1219)*10^-9

t = 0.4539*10^-9 sec

t = 0.46 ns