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PHY 113 C Fall 2013 -- Lecture 25 112/93/2013
PHY 113 C General Physics I11 AM – 12:15 PM MWF Olin 101
Plan for Lecture 25:1. Comments on Exam 32. Pep talk on preparing for Final Exam3. Comprehensive review – Part I
Bonus attendance points for Lecture 26 – Part II of comprehensive review & course assessment
PHY 113 C Fall 2013 -- Lecture 25 412/93/2013
Comments on Final Exam It will be comprehensive (covering material
from Chapters 1-22) It is scheduled for 9 AM Dec. 12th in Olin 101 In class format, but there will be no time
pressure May bring equation sheets according to your
vote
PHY 113 C Fall 2013 -- Lecture 25 512/93/2013
Comments on Exam 3
iclicker questionWhich of the following statements matches your recollections of the exam:
A. It was too hardB. It was too easyC. The Thanksgiving holiday erased all
recollections of the exam
Solutions are now posted: http://users.wfu.edu/natalie/f13phy113/solutions/
PHY 113 C Fall 2013 -- Lecture 25 912/93/2013
Take home portion of Exam 3 – continued
Two problems with question:1. Round-off error in adiabatic step
2. Error in Lecture 21 notes (now corrected)
2940.01952503
2m 0123.0
:process adiabaticFor
5.1/13
/1
C
AAC
CCAA
P
PVV
VPVP
PHY 113 C Fall 2013 -- Lecture 25 1012/93/2013
Work done on a system which is an ideal gas:
“Adiabatic” (no heat flow in the process process)P
(1.
013
x 10
5)
Pa
Pi
Vi Vf
Qi®f = 0
11
1
i
fii
V
V
ii
V
V
fi V
VVPdV
V
VPPdVW
f
i
f
i
For ideal gas:
PVg = PiVig
1
11
f
iii
V
VVP
Corrected equations from #21:
PHY 113 C Fall 2013 -- Lecture 25 1112/93/2013
Further comments on adiabatic processes
since :Note
11
1
1
11
0 :process adiabaticFor
:amics thermodynof lawFirst
int
1
1
int
int
int
CCAAACAC
C
AAA
V
V
AA
V
V
AA
V
V
AC
CCAAAC
ACACAC
ACACAC
VPVPEW
V
VVP
VVP
V
dVVPPdVW
VPVPE
WEQ
WQE
A
C
A
C
A
C
PHY 113 C Fall 2013 -- Lecture 25 1312/93/2013
iclicker question
This problem A. Of all the problems that might appear on the final
exam, this one would be the worst.B. Of all the problems that might appear on the final
exam, this one would not be the worst.C. This example has inspired me to look into designing
better engines or heat pumps.
PHY 113 C Fall 2013 -- Lecture 25 1512/93/2013
In-class portion of Exam 3 -- continued
Ssound
Osound
vv
vvff
'
toward
away
PHY 113 C Fall 2013 -- Lecture 25 1612/93/2013
In-class portion of Exam 3 -- continued
VS
f’=560 HzVS
f’=480 Hz
PHY 113 C Fall 2013 -- Lecture 25 1712/93/2013
Hzf
smvf
f
vv
vv
vv
vff
vv
vff
v
Safter
before
Ssound
Ssound
Ssound
soundafter
Ssound
soundbefore
O
92.516
/38.26 1666666.1480
560
'
'
' '
0 case, In this
VS
f’=560 HzVS
f’=480 Hz
PHY 113 C Fall 2013 -- Lecture 25 1812/93/2013
In-class portion of Exam 3 -- continued
N 10.6166
3
2
3
1
gVgVF BAB
PHY 113 C Fall 2013 -- Lecture 25 1912/93/2013
In-class portion of Exam 3 -- continued
kg083.1m/s 9.8
N 10.6166
0
2
g
Fm
Fmg
mgF
B
B
B
FB
mg
PHY 113 C Fall 2013 -- Lecture 25 2012/93/2013
In-class portion of Exam 3 -- continued
33
kg/m 6666.2166m 0.0005
kg083.1
V
msolid
iclicker questionA. This density seems correct.B. This density seems wrong.
PHY 113 C Fall 2013 -- Lecture 25 2112/93/2013
In-class portion of Exam 3 -- continued
ffo TCTC
iCi QQQQQ
ooo 100water 0 ice meltedicemelt 00.5- ice
0
CT
TTQo
f
ff
04.60
10041867.0041862.03330002.05.0020902.00
PHY 113 C Fall 2013 -- Lecture 25 2212/93/2013
In-class portion of Exam 3 -- continued
ffo TCTC
iCi QQQQQ
ooo 100water 0 ice meltedicemelt 010- ice
0
kgm
mmmQ
76.0
1001041868.0010418633300010020900
PHY 113 C Fall 2013 -- Lecture 25 2312/93/2013
Back to the discussion of the Final exam:
iclicker question
What is the purpose of the Final Exam?A. Pure pain and sufferingB. Assessment of student learningC. Gateway to medical school or other
professional careerD. Help students to “solidify” knowledge of
physics and further develop problem solving skills
E. All of the these
PHY 113 C Fall 2013 -- Lecture 25 2412/93/2013
iclicker question
How many equation sheets should you prepare for Final Exam?
A. 0B. 1C. 2D. 3E. 4
PHY 113 C Fall 2013 -- Lecture 25 2512/93/2013
General advice on how to prepare for Final Exam
Review fundamental concepts and their corresponding equations
Develop equation sheet(s) that helps you solve example problems on all of the material. You can assume that empirical constants and parameters will be given to you; they need not take up space on your equation sheet.
Practice problem solving techniques. If you discover unanswered questions, please
contact me.
PHY 113 C Fall 2013 -- Lecture 2512/93/2013
Advice:
1. Keep basic concepts and equations at the top of your head.
2. Practice problem solving and math skills
3. Develop an equation sheet that you can consult.
Equation Sheet
dt
ddt
d
m
rv
va
aF
Problem solving skills
Math skills
26
PHY 113 C Fall 2013 -- Lecture 25 2712/93/2013
Problem solving steps
1.Visualize problem – labeling variables2.Determine which basic physical principle(s) apply3.Write down the appropriate equations using the
variables defined in step 1.4.Check whether you have the correct amount of
information to solve the problem (same number of knowns and unknowns).
5.Solve the equations.6.Check whether your answer makes sense (units,
order of magnitude, etc.).
PHY 113 C Fall 2013 -- Lecture 25 2812/93/2013
Specific review material -- standing sound waves
General wave equation:
),(
2
22
2
2
x
yc
t
y
txyy
wave propagation distance
time
wave speed
PHY 113 C Fall 2013 -- Lecture 25 2912/93/2013
Specific review material -- standing sound waves
Periodic wave:
cf ftx
ytxy
cTT
txytxy
φλ
π2sin),(
or
λ φ
λπ2sin),(
0
0
cTT
txytxy
λ φ
λπ2sin),( 0
Periodic traveling waves:
Amplitude
wave length (m)
period (s); T = 1/f
phase (radians)
velocity (m/s)
PHY 113 C Fall 2013 -- Lecture 25 3012/93/2013
T
txytxy
T
txytxy leftright λ
π2sin),( λ
π2sin),( 00
T
txytxtxy leftright
π2cos
λ
π2sin2),(y),( 0
“Standing” wave:
Combinations of waves (“superposition”)
BABABA 21
21 cossin2sinsin
: thatNote
PHY 113 C Fall 2013 -- Lecture 25 3112/93/2013
Specific review material -- standing sound waves
open-open open-closed
y(x,t) is density fluctuations in the air v=vsound » 343 m/s
PHY 113 C Fall 2013 -- Lecture 25 3212/93/2013
Specific review material -- standing string waves (which can couple to sound) L
L
vn
vf
nn
L
string
n
stringn
n
2
....3,2,1 2
PHY 113 C Fall 2013 -- Lecture 25 3312/93/2013
iclicker questionHow can we hear a standing wave on a string?
A. The string couples to the air to produce a sound wave at the same wavelength
B. The string couples to the air to produce a sound wave at the same frequency
C. You cannot hear a standing wave on a string
pv
Tv
sound
string