Diffraction AP Physics 2 MCQ – Exam Style Questions etc.
Diffraction AP Physics 2 MCQ
Unit 14: Waves , Sound , and Physical Optics
Weightage : 15–18%
Exam Style Practice Questions ,Diffraction AP Physics 2 MCQ
Questions
A beam of electrons is moving at a speed of \(6\times10^{6}\frac{m}{s}\). If the beam is incident on each of the following objects, for which of the objects will diffraction be observed? Select two answers.
(A) A human hair (diameter about \(10^{-5}\) m )
(B) A metal crystal (interatomic spacing about \(10^{-10}\))
(C) A nanometer-width slit (size about \(10^{-9}\)m )
(D) A narrow paper strip (width about \(10^{-3}\)m )
▶️Answer/Explanation
Ans: B and C
B: This option is correct. An electron moving at \(6\frac{m}{s}\) has a de Broglie wavelength (\(\lambda =\frac{h}{p}\)) as calculated:
\((\lambda =6.63\times10^{-34}j.s)\) / \((9.11\times 10^{-31}kg)\) \((6\times 10^{6}\frac{m}{s})=1.2\times10 ^{-10}m\)
The opening must be small (within several orders of magnitude of the wavelength). The width of the interatomic spacing in the crystal is close enough to the wavelength for interference diffraction to occur, as shown by the well known Davisson-Germer experiment.
C: This option is correct. An electron at the speed given has a de Broglie wavelength (\(\lambda =\frac{h}{p}\)) . Using the mass of an electron and Planck’s constant:
\((\lambda =6.63\times10^{-34}j.s)\) / \((9.11\times 10^{-31}kg)\) \((6\times 10^{6}\frac{m}{s})=1.2\times10 ^{-10}m\)
The opening must be small (within several orders of magnitude of the wavelength). The width of the slit is within about one order of magnitude larger than the wavelength, so diffraction of electrons could occur.
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.