Diffraction AP Physics 2 FRQ

Diffraction AP Physics 2 FRQ – Exam Style Questions etc.

Diffraction AP Physics 2 FRQ

Unit 14: Waves , Sound , and Physical Optics

Weightage : 15–18%

AP Physics 2 Exam Style Questions – All Topics

Question

A student is given a loudspeaker with a square opening and asked to make a change in the dimensions of the opening so that the sound wave is more spread out vertically and narrowed horizontally. Which of the following is the correct use of the principle of diffraction to accomplish the desired result?

(A) The task is impossible since diffraction affects only electromagnetic radiation and very short wavelengths.
(B) Make the opening into a rectangle with a longer vertical dimension and a shorter horizontal dimension.
(C) Make the opening into a rectangle with a longer horizontal dimension and a shorter vertical dimension.
(D) Keep the opening in the shape of a square, but reduce both the horizontal and vertical dimensions.

Answer/Explanation

Ans:C

Question

A shadow is formed by a point source of light. Upon closer inspection, the edges of the shadow seem to be diffuse and fuzzy. This phenomenon is probably caused by
(A) dispersion as the different wavelengths of light focus at different points
(B) refraction as the rays are bent by their contact with the shadow-forming surface
(C) diffraction as the waves nearest the edge of the shadow-forming surface are sources for waves going into the shadow region
(D) dispersion as the different wavelengths are traveling at slightly different speeds in the new medium

Answer/Explanation

Ans:(C)

Diffraction is the bending of wave fronts around obstacles or through openings. In this case, diffraction occurs around the edges of the object causing the shadow. This will cause the edge of the shadow to be slightly less than fully dark at the edges.

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

As the number of lines per cm on a diffraction grating is increased (or the slit spacing is decreased in a two-slit diffraction pattern),
(A) the spacing between the spectral lines increases
(B) the spacing between the spectral lines decreases
(C) the intensity of the spectral lines increases
(D) the intensity of the spectral lines decreases

Answer/Explanation

Ans:

(A)

Remember that d sin θ = mλ . Since d is getting smaller as the number of lines per cm increases, sin θ is getting bigger—spreading out the peaks.

Question

Light with a wavelength of 5.4 × \(10^{-7}\) meters falls on two slits that are separated by a distance of 1.0 × \(10^{-3}\) meters. An interference pattern forms on a screen 2 meters away.

The dark and bright interference pattern observed on the screen is caused by
(A) reflection and refraction
(B) refraction and diffraction
(C) polarization and interference
(D) diffraction and interference

Answer/Explanation

Ans:(D)

The diffracted light from each slit spreads out and interferes with the light from the other slit to produce the pattern.

Diffraction AP Physics 2 FRQ