PHY 113 C General Physics I 11 AM – 12:15 PM MWF Olin 101...

12/93/2013 PHY 113 C Fall 2013 -- Lecture 25 1

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


Final exam schedule for PHY 113 C


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


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/


Two versions of take-home portion of exam


Take home portion of Exam 3 -- continued


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

2m0123.0

:processadiabaticFor

5.1/13/1

C

AAC

CCAA

PPVV

VPVP


Work done on a system which is an ideal gas:

“Adiabatic” (no heat flow in the process process)P

(1.0

13 x

105

) Pa

Pi

Vi Vf

Qif = 0

11

1

i

fiiV

V

iiV

Vfi V

VVPdVVVPPdVW

f

i

f

i

For ideal gas:

PV = PiVi

1

11

f

iii

VVVP

Corrected equations from #21:


Further comments on adiabatic processes

since:Note

11

11

11

0:processadiabaticFor :amics thermodynoflawFirst

int

1

1

int

int

int

CCAAACAC

C

AAA

V

VAA

V

VAA

V

VAC

CCAAAC

ACACAC

ACACAC

VPVPEW

VVVP

VVP

VdVVPPdVW

VPVPE

WEQWQE

A

C

A

C

A

C


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.


In-class portion of Exam 3


In-class portion of Exam 3 -- continued

Ssound

Osound

vvvvff

'

towardaway



VS

f’=560 HzVS

f’=480 Hz


Hzf

smvff

vvvv

vvvff

vvvff

v

Safter

before

Ssound

Ssound

Ssound

soundafter

Ssound

soundbefore

O

92.516

/38.261666666.1480560

''

''

0case,In this

VS

f’=560 HzVS

f’=480 Hz



N10.616632

31

gVgVF BAB



kg083.1m/s9.8

N10.6166

0

2

gFm

FmgmgF

B

B

B

FB

mg



33 kg/m6666.2166

m0.0005kg083.1

Vm

solid

iclicker questionA. This density seems correct.B. This density seems wrong.



ffo TCTC

iCi QQQQQ

ooo 100water 0icemeltedicemelt 00.5-ice0

CT

TTQo

f

ff

04.60

10041867.0041862.03330002.05.0020902.00



ffo TCTC

iCi QQQQQ

ooo 100water 0icemeltedicemelt 010-ice

0

kgm

mmmQ76.0

1001041868.0010418633300010020900


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


iclicker question

How many equation sheets should you prepare for Final Exam?

A. 0B. 1C. 2D. 3E. 4


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.

12/93/2013

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

dtddtdm

rv

va

aF

Problem solving skills

Math skills

26PHY 113 C Fall 2013 -- Lecture 25


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.).


Specific review material -- standing sound waves

General wave equation:

),(

2

22

2

2

xyc

ty

txyy

wave propagation distance

time

wave speed



Periodic wave:

cfftxytxy

cTT

txytxy

φλ

π2sin),(

or

λφλ

π2sin),(

0

0

cTT

txytxy

λφλ

π2sin),( 0

Periodic traveling waves:

Amplitude

wave length (m)

period (s); T = 1/f

phase (radians)

velocity (m/s)


Ttxytxy

Ttxytxy leftright λ

π2sin),(λ

π2sin),( 00

Ttxytxtxy leftright

π2cosλπ2sin2),(y),( 0

“Standing” wave:

Combinations of waves (“superposition”)

BABABA 21

21 cossin2sinsin

: thatNote



open-open open-closed

y(x,t) is density fluctuations in the airv=vsound 343 m/s


Specific review material -- standing string waves (which can couple to sound) L

Lv

nv

f

nnL

string

n

stringn

n

2

....3,2,12


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


Bonus attendance points for Lecture 26 – Part II of comprehensive review & course assessment

Bonus points for emailing in questions you would like to discuss in Lecture 26

PHY 113 C General Physics I 11 AM – 12:15 PM MWF Olin 101...

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