Thin-Film Interference AP Physics 2 FRQ – Exam Style Questions etc.
Thin-Film Interference AP Physics 2 FRQ
Unit 14: Waves , Sound , and Physical Optics
Weightage : 15–18%
Exam Style Practice Questions ,Thin-Film Interference AP Physics 2 FRQ
Question
The colors observed in thin films like soap bubbles are caused by
(A) reflection and interference
(B) refraction and reflection
(C) diffraction and interference
(D) polarization and reflection
Answer/Explanation
Ans:(A)
The interference between the ray reflecting off of the top boundary and another ray bouncing off of the lower boundary either produces some bright colors (constructive interference) or does not produce certain colors (destructive interference).
Question
Two sources, in phase and a distance d apart, each emit a wave of wavelength λ. See figure below. Which of the choices for the path difference ∆L = L1 – L2 will always produce destructive interference at point P?
A) d sin θ B) (x/L2)d C) λ/2 D) 2 λ
Answer/Explanation
Ans:D
Solution: By definition, when the path difference equals ½ λ or any odd multiple of ½ λ’s for sources of the same λ, there will be destructive interference.