Note: This Laboratory will be used for your required “Formal Lab” in Physics. You will
be allowed one partner for this lab. Each person will complete his/her own laboratory
report according to the requirements of the FHS Science Department. Bolded items are
required. Helpful hints and instructions follow each bolded item where necessary. Use 12
pt. Times New Roman font, 1 inch margins, full sentences and correct grammar. Avoid
use of the words “I”, “We” and “Us”.
Lab Title: Determination of the Width of a Human Hair
Your Name:_____________________________________________
Name of Partner:_______________________________________
Academic Physics, Block #____________________________
Mrs. Broczkowski
Due Date:________________________________________________
Introductory Paragraph(s): Use Section 16.2 to help you write this part. Be sure to
include:
 What is diffraction?
 Describe Young’s experiment and his discoveries related to diffraction and
interference.
 Discuss how light which is diffracted by an obstacle can also produce a pattern.
 Write the equation used in this laboratory describing what each variable stands
for: (you do not need to look this up – copy it from below)
Y= mX
d
Where
Y is the distance between the central bright fringe and
the mth dark fringe
m is the order number (central bright fringe is the 0th order)
X is the distance from the slide to the screen
d is the thickness of the hair
 is the wavelength of the laser light
Objective: Copy from below.
In this lab the width of a human hair will be determined using knowledge of single slit
diffraction and interference of waves.
Hypothesis: Conduct research to find out the typical width of your hair type. Cite
source(s). State the hypothesis as “If the width of human hair is determined
experimentally, then____________________________________________________”
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Materials (Copy from below)
Laser Pointer (known)
Piece of clay
Meter stick
Stand and Clamp
Ruler
A Human Hair
Screen
Slide
Tape
Procedure (Copy from below)
1. Set up the equipment as shown below
screen
Hair mounted
vertically on slide
laser
2. Mount a human hair on the slide in a vertical position.
3. Set the slide on the clay near the end of the laser and position the screen at the end of
your lab bench or against the wall. Your laser should be clamped in a horizontal position
the same height as the middle of the slide. Target the laser light at the hair.
4. Record the average wavelength of your laser in the data table.
5. Record X in the data table.
6. Shine the laser at the hair on the screen. Observe the interference pattern on
the screen.
7. Measure Y for 5 different dark fringes of order number, m, on one side of the
bright central fringe. Record m and Y in the data table for each dark fringe.
Data/Results/Observations
Quantitative Results: Copy and fill in with your data.
 = ___________________
X = __________________
m
1
2
3
4
5
Y (m)
d (m)
Average
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Qualitative Results: Describe what you saw happen and anything that might lead to
error.
Analysis/Calculations:
1. Solve for d for each value of m in the data table. Record in the data table.
Show an example calculation (full work) for m = 1
2. Average the five values for d and record in the table.
Conclusion:




Compare your value to the literature range of values for human hair.
Provide a one-line sentence that supports or rejects the hypothesis
Describe at least 2 possible sources of scientific error that might have occurred.
Discuss what you learned from the experiment.
Works Cited: List all sources of information in MLA format.
Example: Kane, Joseph W. and Morton M. Sternheim.Physics. New York: John
Wiley & Sons, 1984. Print
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