Physics final exam problem: hair diffraction

Physics 205B Final Exam, fall semester 2010
Cuesta College, San Luis Obispo, CA

Cf. Giambattista/Richardson/Richardson, Physics, 2/e, Problem 25.47

Shown at right is a scaled diagram[*] of the diffraction pattern of hair illuminated by a 610 nm wavelength laser. The screen is 4.40 m from the hair. Find the width of the hair. Show your work and explain your reasoning using trigonometry and the properties of diffraction.

[*] en.wikipedia.org/wiki/File:Diffraction1.png.

Solution and grading rubric:

• p:
  Correct.
  
• r:
  Nearly correct, but includes minor math errors. May have used angle of first maxima instead of first minima in W·sinθ = (1)·λ.
  
• t:
  Nearly correct, but approach has conceptual errors, and/or major/compounded math errors.
  
• v:
  Implementation of right ideas, but in an inconsistent, incomplete, or unorganized manner.
  
• x:
  Implementation of ideas, but credit given for effort rather than merit.
  
• y:
  Irrelevant discussion/effectively blank.
  
• z:
  Blank.
  

Grading distribution
Section 70856
Exam code: finalv0L7
p: 4 students
r: 2 students
t: 3 students
v: 0 students
x: 0 students
y: 0 students
z: 1 student

A sample "p" response (from student 0057) with a minor cm to m transcription error for the hair-to-screen distance: