Double-Slit Interference and Diffraction Gratings AP Physics 2 FRQ – Exam Style Questions etc.
Double-Slit Interference and Diffraction Gratings AP Physics 2 FRQ
Unit 14: Waves , Sound , and Physical Optics
Weightage : 15–18%
Exam Style Practice Questions ,Double-Slit Interference and Diffraction Gratings AP Physics 2 FRQ
Question
Which of the following changes to a double-slit interference experiment would increase the widths of the fringes in the interference pattern that appears on the screen?
(A) Use light of a shorter wavelength.
(B) Move the screen closer to the slits.
(C) Move the slits closer together.
(D) Use light with a lower wave speed.
Answer/Explanation
Ans:C
Relative to the central maximum, the locations of the bright fringes on the screen are given by the expression m\(\left ( \frac{\lambda L}{d} \right ),\) where A is the wavelength, L is the distance to the screen, d is the slit separation, and m is any integer. The width of a fringe is therefore ( m + 1 ) \(\left ( \frac{\lambda L}{d} \right )-m\left ( \frac{\lambda L}{d} \right )=\left ( \frac{\lambda L}{d} \right ).\) The slit spacing will increase if there is a decrease in d.
Question
In a double slit experiment, students are attempting to increase the spacing of the fringes observed on the screen. Which modifications to the set up will result in increased fringe separation? Select two answers.
(A) Doubling the wavelength only
(B) Doubling the wavelength and doubling the slit separation
( C) Doubling the distance to the screen only
(D) Doubling the distance to the screen and doubling the slit separation
Answer/Explanation
Ans:A, C
For the double slit experiment, mλ = dsin(θ) →mλ =dx\L. The spacing of the fringes, x, increases for increasing λ and L and decreases by increasing d.