Transcript Physics 2015 – General Physics Lab 1 Introductory Meeting

Modern Optics Lab
Introductory Meeting
Modern Optics Lab
Contact Information
Gernot Laicher
South Physics 410
(801) 585-5553
[email protected]
TAs:
Joel Brownstein (Wednesday Section)
[email protected]
Bijaha Thapa (Thursday Section)
[email protected]
Bryant Svedin (Tuesday and Friday Sections)
[email protected]
Website:
http://www.physics.utah.edu/~gernot/Modern Optics/Modern Optics.html
Modern Optics Lab
Lab Format
•
Lab descriptions will be on our website (pdf files).
•
Before the lab:
* Read through lab description.
* Try to understand the principle of the experiment and the
data evaluation methods.
* Think about the format of your lab report.
•
Labs are done individually, not in groups.
•
A short introduction/overview to the lab activity is usually given at
the beginning of the lab.
•
Lab report is written as much as possible during the lab. Submission
deadline is 1 week after lab completion.
•
9 labs (11 lab sessions) are planned over the course of the class
(may vary).
Modern Optics Lab
Grading in Modern Optics
•
•
•
•
Quizzes: 15%
Midterm Exams: 20%
Final Exam: 30%
Lab Grade: 35%
•
Your lab score is obtained as follows:
90%: Grade received for lab reports
10%: General Lab conduct
- Displayed interest/diligence in lab activity
- Ability to answer questions asked by TA
- Cleanliness of workspace at the end of the lab
- Creativity
- Punctuality
There is a 10% grade deduction for every day the lab report is late.
Modern Optics Lab
Guidelines for Writing the Lab Report
•
Keep in mind the main purpose of a lab report which is a written record of the
a) purpose of the lab activity,
b) methods and techniques - experimentally and mathematically,
c) raw data as measured and their uncertainties,
d) data analysis (e.g., computations) including error propagation,
e) conclusions derived from your data analysis.
•
“Say what needs to be said” as efficiently, concise, and clear as possible – we
are not writing novels.
•
A picture is worth a thousand words:
Include a sketch of the apparatus when describing the methods.
Label what’s on the sketch.
•
Don’t forget units !
•
Don’t submit messy lab reports in which the TA needs to “fish for information”.
Modern Optics Lab
Lab Report Grading
•
General guideline (may vary somewhat depending on lab activity and TA):
20% Purpose, Methods, Techniques …..
30% Raw Data Record
20% Data Analysis
10% Error calculation
- Measurement uncertainties in raw data
- Propagation of error
20% General appearance and organization
- Legible ?
- Looks organized ?
- Easy to follow ?
Modern Optics Lab
Missing a lab due to Illness, etc.
• Arrange with the TA a way to make up the missed
lab activity.
- If possible, in another section the same week.
- Alternatively a time outside the regular lab
hours may be arranged between you and TA.
- Worst case: We may waive a lab and base your
grade on the remaining average.
You cannot expect to be allowed to make up a lab
activity without penalty unless you have a very
good reason (illness, etc.).
Modern Optics Lab
Sample Lab Report Pages
Modern Optics Lab
Significant Figures and Uncertainty
• Report uncertainties (error) in measurements to
one significant digit
• Make sure the position of the least significant
digit of the measured value agrees with that of
the uncertainty.
x  5.8  0.4cm
Modern Optics Lab
Estimating and Reporting Uncertainty
• Estimation of uncertainty from a single
measurement due to measuring device (e.g., ability
to read out a scale)
• Uncertainty in repeated measurements and
averaging (averaging 5 or more measurements to
get mean)
 calculate standard deviation of the mean
x
x
N
 x  Standard deviationof themean
 x  Standarddeviation
Modern Optics Lab
Error Propagation
• Calculating the error in the final result based on
the error in the measured quantity can be done in
several ways.
a) Calculate the “high” and “low” possible
outcome based on using extreme values of
input data (x+x and x-x).
b) Doing a “proper” error calculation.
Modern Optics Lab
“High/Low” Method
Suppose you measure a quantity and it’s uncertainty
xo  xo
….and you want to calculate the value of a function f(x) and the
uncertainty f of the function f(x) at the point x=xo
f x   x 2
xo  2.5  0.3
Modern Optics Lab
15
f(x)=x^2
10
f(x)
f xo   xo 
f xo 
5
f xo   xo 
0
0
1
2
xo   xo
Modern Optics Lab
xo
3
xo   xo
x
4
2  f xo 
 f ' xo    f xo   f ' xo  xo 
2  xo
15
f(x)=x^2
10
f ' xo 
f xo   xo 
f(x)
f xo 
 f ' xo  xo 2
2  f xo 
5
f xo   xo 
0
0
1
2
xo
2 xo
Modern Optics Lab
3
x
4
General Error Propagation Method
f x   ........
 df 
 f ( x )   x 
 dx 
2
f x, y, z......  ........
2
 f   f   f 
 f ( x, y, z...)   x    y    z  ...
 x   y   z 
2
Modern Optics Lab
2
Example
n1 sin 1  n2 sin  2
n1  1.52  0.03
n2 
1  34.2  0.4 
 2  27.4  0.6 
2
n1 sin 1 1.52  sin 34.2

 1.8565.....
sin 2
sin 27.4
2
 n2
  n
  n

n1    2 1    2 2 
 n1
  1
  2

2
 n2  
n2 sin 1 sin 34.2


 1.221
n1 sin  2 sin 27.4
n2 n1 cos1 1.52  cos34.2


 2.732
1
sin  2
sin 27.4
n2 n1 sin 1
1.52  sin 34.2

cos


cos27.4  3.582
2
2
2
 2 sin  2
sin 27.4
Modern Optics Lab
Example
n1 sin 1  n2 sin  2
n1  1.52  0.03
n2 
1  34.2  0.4 
 2  27.4  0.6 
n1 sin 1 1.52  sin 34.2

 1.8565.....
sin 2
sin 27.4
  
 

 n2  1.221 0.03   2.732 0.4

3
.
582

0
.
6

 

180

180


 

 0.056
2
2

n2  1.86  .06
Modern Optics Lab
2
Example using “High/Low” Method
n1 sin 1  n2 sin  2
n1  1.52  0.03
1  34.2  0.4 
 2  27.4  0.6 

n1   n1 sin 1   1  1.55 sin 34.6
n2,max 

 1.952....
sin  2    2 
sin 26.8
n   n1 sin 1   1   1.49 sin 33.8  1.766....
n2,min  1
sin  2    2 
sin 28.0
n2 
n2,max  n2,min
2

1.952 1.766
 0.09
2

n2  1.86  .09
Modern Optics Lab
Method overestimates
error somewhat