A sheet of glass is coated with a 505nm thick layer of oil (n = 1.42).
For what visible wavelengths of light do the reflected waves interfere constructively/destructively?
For constructive interference
For destructive interference
The Attempt at a Solution
2*1.42*505/(3 or 4) (since m=3 and 4 will give me a visible wavelength) lamba = 717 nm, 478 nm
2*1.142*505/(3 or 4 + 1/2) (since m=3 and 4 will also give me a visible wavelength) lamba = 574, 410 nm
HOWEVER, they are wrong... so im completely clueless of what to do next.. help please >.<