Answer:
they indicate that the thickness is much less than the length of anything we have a destructive interference, bone has a dark area
Explanation:
Let's analyze the interaction of the ray reflected on the surface of the oil and at the bottom of the film, to know what kind of interference we have.
- When the beam passes from the air to the oil film, it has a phase change of 180 since the refractive index of the oil is greater than the refractive index of the air n = 1
- When the beam reaches the oil-water interface, the refractive impact of the water is oil cobs, therefore it has a 180 phase change
- in the oil film because the speed of the beam is different from that of air and the frequency in the air and oil is the same, since the propagation of a resonant type process, to meet the equation
v = λ f
The wavelength must change c = λ₀ f
c / v = λ₀ /λ
n = λ₀ /λ
λₙ = λ₀ / n
In general this type of reflection is almost normal to the surface, so we can calculate the optical path difference, if t is the thickness of the film, for constructive interference
2t = m λₙ + λₙ / 2 + λₙ / 2
The last two terms are for the phase change
2t / = (m + 1) λₙ
This is the condition to see a bright beam
For the first reflection m = 0
2t = λₙ
Therefore the minimum thickness of the film for constructive interference is λₙ / 2.
As they indicate that the thickness is much less than the length of anything we have a destructive interference, bone has a dark area
