Question

When I shine a green laser pointer (wavelength 532nm) on two slits, I find that what should be the central bright spot is actually a dark spot. Upon further investigation, I discover that there's a thin layer of oil covering one of the slits. The oil has an index of refraction of 1.5. What is the minimum thickness of the oil that would cause the observed effect

Answer 1

t = 88.7 nm

Step-by-step explanation:

`\lambda` = wavelength = 532 nm

n = index of refraction of oil = 1.5

t = minimum thickness of oil

m = order

Using the equation

2 n t = (2m + 1) (
`\lambda`/2)

for minimum , m = 0

2 n t = (2(0) + 1)(
`\lambda`/2)

`\lambda` = 4 nt

532 = 4 (1.5) t

t = 88.7 nm