AP physics 2: Phase change in thin film interference

  • Thread starter Thread starter AAONA
  • Start date Start date
AI Thread Summary
When light reflects off a boundary from a medium of lower refractive index to a higher one, a 180° phase change occurs. In this scenario, light travels from air to the first layer (n₁ = 1.404) and then reflects off the glass (n_glass = 1.62). The reflection at the glass interface results in a 180° phase change, while the transition from air to the first layer does not induce a phase change. Therefore, the total phase change for light reflecting from the glass is 180°. The confusion arises from not accounting for the direction of light travel and the phase changes at each interface correctly.
AAONA
Messages
1
Reaction score
0
Homework Statement
Phase change in thin film interference
Relevant Equations
2t=. 5m/wavelength

180° phase change if n2>n1
47. Two thin layers of material with different indices of refraction are coated on a glass plate. The outer first material has n₁ = 1.404, the inner second material has n₂ = 1.531, and the glass has glass = 1.62. If light is incident from air on the first layer, what is the phase change for light that reflects from the glass?

a. 0°

b. 180°

c. 360°

d. 540°

Apparently the answer is 180, but I don't get it. I assumed since it's low n» high» higher > two consecutive 180° phase changes since moving to a denser meduim produces a 180° phase change, so 360° which is equivalent to zero.


What am I missing?
 
Physics news on Phys.org
The questions asks about the light reflected from the glass, so must traverse the layers in the opposite direction as well.
 
  • Like
Likes AAONA, SammyS and berkeman
Kindly see the attached pdf. My attempt to solve it, is in it. I'm wondering if my solution is right. My idea is this: At any point of time, the ball may be assumed to be at an incline which is at an angle of θ(kindly see both the pics in the pdf file). The value of θ will continuously change and so will the value of friction. I'm not able to figure out, why my solution is wrong, if it is wrong .
Thread 'Correct statement about a reservoir with an outlet pipe'
The answer to this question is statements (ii) and (iv) are correct. (i) This is FALSE because the speed of water in the tap is greater than speed at the water surface (ii) I don't even understand this statement. What does the "seal" part have to do with water flowing out? Won't the water still flow out through the tap until the tank is empty whether the reservoir is sealed or not? (iii) In my opinion, this statement would be correct. Increasing the gravitational potential energy of the...
Thread 'A bead-mass oscillatory system problem'
I can't figure out how to find the velocity of the particle at 37 degrees. Basically the bead moves with velocity towards right let's call it v1. The particle moves with some velocity v2. In frame of the bead, the particle is performing circular motion. So v of particle wrt bead would be perpendicular to the string. But how would I find the velocity of particle in ground frame? I tried using vectors to figure it out and the angle is coming out to be extremely long. One equation is by work...
Back
Top