Transcript Orientation for Physics Lab for Engineers (Auto and Nano program)

Orientation for
Physics Lab for Engineers
2304 193, 194 and 169
Email: [email protected]
This document is available at Physicslab Homepage
http://www.physicslab.sc.chula.ac.th
1
A Glimpse of Physics
Experiments
Why experiment is important?

Experiment is used to identify a value of unknown quantity from the
known physics formula, i.e. to find a gravitational constant (g) from a
swing of pendulum, using an equation
T  2



l
g
Results from experiments can help formulate the relationship
between two quantities, despite precise formula is yet to be
identified.
It is well accepated that any new theory/hypothesis must be
physically verified by a real observation (experiment).
Sometimes, an advanced experiment can lead to a new physics
phenomenon.
3
Goals of the physics lab courses
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Measurement skills that minimize errors - discrepancy between
result and theoretical values.
The use of instruments - understand how it works and basic
operation.
Data recording with appropriate accuracy and precision.
Error analysis of the results.
Data analysis by statistical and graphical methods.
Gaining physics concept
4
Important Accessories
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Pen
Pencil
Rubber/Eraser
Transparent Ruler
Scientific Calculator
etc.
List of
Exp.No
st
1
Year Physics Experiments
Experiment
1
Measurement & Uncertainties
2
Simple Pendulum, Linear Graph and
Statistical Analysis
4
Simple Harmonic & Hooke's Law
5
Moment of Inertia
6
Central Force
7
PostTest
Yes
EN IND
ENG G19 A16
193
4
9
1
1
1
No
2
2
2
No
4
4
4
5
5
5
No
6
6
6
Rotational Motion
No
7
7
7
9
Standing Waves
No
9
9
9
10
Viscosity of Fluid
No
10
10
10
21
Heat Capacity
No
21
21
21
22
Sound Waves (Beats & Fourier
Analysis)
No
22
22
22
Yes
List of
Exp.N
o
st
1
Year Physics Experiments
Experiment
11
Electrical Measurement
13
Ammeter & Voltmeter
14
Basic Oscilloscope Operation
15
Alternating Current
17
Lenses and Spherical Mirrors
18
Polarization of Light
19
Interference and Diffraction of Light
31
Electrical Field Lines nd Equipotential
Lines
33
Transistor and Semiconductor Devices
35
Electromagnetic Induction
PostTest
Yes
EN EN
G19 G19
3
4
IND
A16
9
11
11
11
No
13
13
13
No
14
14
14
Yes
15
15
15
Yes
17
17
17
18
18
18
Yes
19
19
19
Yes
31
31
31
No
33
33
33
No
35
35
35
No
Lab Schedule
Lab. Schedule 2304194
Wednesday, 9:00 - 12.00 AM
Week
Orientation
1st
**NO LAB**
2nd
3rd
4th
5th
6th
**NO LAB**
7th
8th
9th
10th
Review Lab.
**NO LAB**
Make-up Lab
Date
7-Jan-15
14-Jan-2015
21-Jan-2015
28-Jan-2015
4-Feb-2015
11-Feb-2015
18-Feb-2018
25-Feb-2015
4-Mar-2015
11-Mar-2015
18-Mar-2015
25-Mar-2015
1-Apr-2015
8-Apr-2015
15-Apr-2015
22-Apr-2015
Lab. Schedule 2304169
Friday, 9:00 - 12.00 AM
Week
Orientation
**NO LAB**
**NO LAB**
1st
2nd
3rd
4th
5th
**NO LAB**
6th
7th
8th
9th
10th
Review Lab.
Make-up Lab
Date
9-Jan-15
16-Jan-15
23-Jan-15
30-Jan-2015
6-Feb-2015
13-Feb-2015
20-Feb-2015
27-Feb-2015
06-Mar-2015
13-Mar-2015
20-Mar-2015
27-Mar-2015
03-Apr-2015
10-Apr-15
17-Apr-2015
24-Apr-2015
8
Grading policy

Experimental part (10 Labs) 70 points
 7 points for each lab.
 2 points for general evaluations
 On time for class
 Manner in class
 Behavior in class
 5 points for
 Data sheet
 Post-Test in class (see course syllabus)

Final exam (written)
30 points
9
General rules
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Be in class no later than 10 minutes,
 After 20 minutes is considered being late (1 point reduction).
 After 30 minutes, student is not allowed to enter the lab.
Dress properly according to the university code of uniforms. IF NOT,
you may be refused to enter the lab or 1-2 point of score will be
deduced.
No use of mobile phone/Tablet PC/PC in class.
Do not leave the laboratory room at any time without notifying an
instructor.
Stay at your table until the experiment is finished unless necessary.
Do not make unnecessary loud noise.
No food or drink in the laboratory room.
10
General procedures
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2-3 students per group for each experiment.
Check your lab schedule and partners at the front of room 505, MHMK
Bldg or on the Website http://www.physicslab.sc.chula.ac.th.
Sign your name before getting into the lab room and obtain the data
sheet.
 Sign up for other person is considered cheating! All parties involved
will get a punishment - maximum of 7 pts score deduction. The issue
will also be reported to your course administrator.
In some lab, student is required to sign up for checking out an
experiment kit.
 After finishing the lab, all checked-out items must be returned.
 If damage occurs, student(s) will be held responsible (charge or
replacement).
Submit your data sheet on time (informed at the briefing).
 Do not take your data sheet out of the lab room.
 It is not accepted after the class is already over.
11
A Make-Up Class Policy

If you miss more than 2 classes, you have no right to take the final
examination (<80% attendance). You are advised to “WITHDRAW”
before the final exam, otherwise an F grade will be given.

If you miss any class, please contact the laboratory staff within 7 days
with supporting documents, i.e. a medical certificate, official letter from a
respected organization, etc. sufficiently explaining why you could not
attend the class. The laboratory instructor/staff retains the right to
accept/reject those documents.

Only ONE make-up experiment can be arranged for any student during
the MAKE-UP week. Beware that attending a make-up class does not
necessarily reduce the number of your absences in normal class.
12
Personnel & Staff Security Issue

Threatening or injuring instructors/staffs is a very serious issue. The
issue will be reported to your course administrator and your family. If
seriously, punishment will be executed to the maximum extend by
university law and criminal law.
13
Comments Form
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The comment form is available at every lab room, in a box near the
entrance door.
Student can evaluate or comment on each lab and drop the form
into the box nearby.
Not necessarily do or return the form during the lab. You can take
the form home and drop it at any lab room next time you come to the
lab.
Your comments are important and useful to make things better!
14
Error analysis and graph
Note that the following details appear in
Lab books 2304193 and 2304169 Only
•
•
•
•
•
Types of errors
Preliminary description of error analysis
Propagation of uncertainties
How to report and use uncertainties?
Straight line
15
Types of errors
• Personal error
– Individual mistake - must be avoided or minimized.
• Systematic error - measurement tool
– Calibration should be done.
• Statistical error
– Random uncertainty from repeated measurement.
16
Preliminary Description of
Error Analysis
use error in the sense of “uncertainty”:
error do not involve ‘mistake’ in a
scientific measurement.
no scientific measurement can yield
exact value.
knowing the uncertainty is important!
17
 Example: Is the crown made of gold?
Perform the density measurement of the crown
gold = 15.5 g/cm3 and
Measurement report
alloy = 13.8 g/cm3
Student A
Best estimate of crown 15 g/cm3
Uncertianty() for crown 1.5 g/cm3
alloy
13.8 g/cm3
Student B
13.9 g/cm3
0.2 g/cm3
gold
15.5 g/cm3
density
13.5
16.5
13.7
14.1
Student A
Student B
18
Estimating uncertainties when
reading scales
No specific criteria, up to your confidence.
But try not to underestimate or overestimate it.
reading on a meter 2.2 ± 0.2
(definitely between 2.0 and 2.4)
reading on a ruler 2.77 ± 0.03 cm
(definitely between 2.74 and 2.80 cm)
19
 Estimating uncertainties in repeatable
measurements
 Same quantities obtained from several readings/
repeating.
 Best estimate = average value
 Standard deviation () is 68% confidence limit.
N
 
2
(
x

x
)
 i
i 1
N 1
68 of 100 readings will fall
within x  S.D. and x  S.D.

 Uncertainty of the mean () is
N
20
Propagation of uncertainties
calculation of quantities consisting of
uncertainties:
A =a  a, B=b  b, C=c  c
1. sums or differences (maximum uncertainty)
A+B-C = (a+b-c)  (a+b+c)
example: M1 = 55  1 kg and M2 = 380  30 kg
MT = M1+M2 = (55+380)  MT kg
MT = 1+30 = 31 kg
21
Propagation of uncertainties
2. products or quotients (maximum uncertainty)
A x B = (a x b)  AB
A/B = (a/b)  A/B
 AB
ab

a b
 A/ B
a
a/b

b

a b
a

b
example: W = 1.3  0.1 cm and L= 2.1  0.3 cm
area = WL = (1.3x2.1)  WL cm2 = 2.73  WL cm2
WL / 2.73 = (0.1/1.3) + (0.3/2.1) = 0.2198
WL = 2.73 x 0.2198 = 0.600054  0.6 cm2
22
Propagation of uncertainties
Combined statistical uncertainties
A =a  a, B=b  b, C=c  c
1. sums or differences
X = A + B – C = x  x
2
2
2
x = a + b – c,
x  (a )  (b)  (c)
2. products or quotients
Y = A  B / C = y  y
y = ab / c,
y
y

 a 
 b 
 c 

 
 

 a 
 b 
 c 
2
2
2
23
Propagation of uncertainties
more example:
q = ?
max. uncertainty:
ab
q
y z
q
|q|

a
|a|

b
|b|

y
| y|

z
|z|
stat. uncertainty:
q
2
 a   b   y   z 
           
q
 a   b   y  z 
2
2
2
Read more in your lab manual ...
24
How to report and use uncertainties?
• Always include the units.
(measured value of x) = best estimate  uncertainty
• Rule for stating uncertainties

In an introductory laboratory, experimental
uncertainty usually be rounded to one significant
figure.
example: (measured of g) = 9.82  0.02385 m/s2
should be reported as 9.82  0.02 m/s2 or the
mass of 5.24  0.4637 g should be reported as
5.2  0.5 g
25
How to report and use uncertainties?
• Rule for stating answers
The last significant figure in any stated answer
should usually be of the same order of
magnitude (in the same decimal position) as the
uncertainty.

Example:
best estimate
uncertainty
stated answer
92.855
0.05
92.86  0.05
92.855
0.5
92.9  0.5
92.855
5
93  5
26
How to report and use uncertainties?
• Using scientific notation for a very large
or small value.
Example:
1. (measured charge) = 1.59x10-19  5x10-21 C
should report as (1.59  0.05 ) x 10-19 C
2. 1,857,000  40,000
 1.857 x 106  4 x 104
 ( 1.86  0.04 ) x 106
27
Straight line
• Linear equation: y = m x + c
m is slope and c is y-intercept.
They can be evaluated using either
graphical analysis or statistical analysis
(lab 2).
• Usually, data are plotted to see if they
satisfy linear equation (straight line).
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Best fit for a straight line
30.00
25.00
y
20.00
15.00
10.00
di
• Number of data
points above the
line is about the
same to that of
under the line.
5.00
• Summation of the
0
10
20
30
40
50
60
vertical distances for
x
each data point to
 di2 =  (yline- ydata)2 is minimum the line is minimum.
0.00
29
Best fit :practical approach
• Number of data points above the line is
about the same to that of under the line.
• Summation of the vertical distances for
each data point to the line is minimum.
30
Exercise
• Let
1. What is the unit of z?
2. Write down the formula for the maximum
uncertainty z.
3. Report z and z
31
Homework
• Read the Introduction part in the lab
book (not included in 2304194 lab book).
• Bring your calculator and learn how to
use it to get the mean and standard
deviation of a set of data. 
32
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