improvingefficiencyin instruction: gauss’slaw · 2016-07-26 · improvingefficiencyin...

Improving efficiency ininstruction: Gauss’s law

Marshall J. Styczinski

Physics Education GroupUniversity of Washington

July 18th, 2016AAPT Summer Meeting

Physics

Education

Group

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Tutorials in introductory physics

University of WashingtonIntroductory physics:

3 hrs/week lecture1 hr/week tutorial2 hrs/week lab

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Tutorials in introductory physics

University of WashingtonIntroductory physics

1 hr/week tutorial

Each tutorial addressesknown student difficulties

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Physics

Education

Group

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Physics

Education

Group

10 or fewer weekly tutorials

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Topics to combine

Forces & Newton’s second and third lawsLenz’s law & Faraday’s lawElectric field and flux & ChargeElectric field and flux & Gauss’s law

Marshall Styczinski (U Washington) AAPT Summer Meeting 5 / 16

Topics to combine

Forces & Newton’s second and third lawsLenz’s law & Faraday’s lawElectric field and flux & ChargeElectric field and flux & Gauss’s law

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R1

R2

Q

Non-conductor

Total charge Q spreadthroughout volumeThick spherical shell, insulatorQuestion: Find | ~E| in the shell.

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R1

R2

Q

Non-conductor

Total charge Q spreadthroughout volumeThick spherical shell, insulatorQuestion: Find | ~E| in the shell.

Required concepts:Distributed chargesCharge densitySurface area vs. volume

Electric fieldElectric flux

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R1

R2

Q

Non-conductor

Total charge Q spreadthroughout volumeThick spherical shell, insulatorQuestion: Find | ~E| in the shell.

N = 308

15% obtained a correct expression.< 5% explained how they obtained correct

expressions.

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The literature

The Gauss’s law tutorial improves conceptualunderstanding of Gauss’s law.1

1Kanim, S. (1999)

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The literature

The Gauss’s law tutorial improves conceptualunderstanding of Gauss’s law.1

Helping students learn about symmetry withflux and applicability of Gauss’s law improvesunderstanding and problem solving ability.2

1Kanim, S. (1999)2Singh, C. (2006)

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Gauss’s law tutorial coverage

Flux practice+Q

o

Finding basic Qenc

–Qo

+Qo

–Qo

+Qo

Examplecalculation

+σo

Find ER

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Existing tutorials

Week 1

Week 2

Week 3

Charge

Gauss’s law

Electric field

and flux

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Existing tutorials New tutorials

Week 1

Week 2

Week 3

Charge

Gauss’s law

Charge and

Electric field

and flux

electric field

Flux and

Gauss’s law

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Existing tutorials New tutorials

Week 1

Week 2

Week 3

Charge

Gauss’s law

Charge and

Electric field

and flux

electric field

Flux and

Gauss’s law

New content!

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Existing tutorials New tutorials

Week 1

Week 2

Week 3

Charge

Gauss’s law

Charge and

Electric field

and flux

electric field

Flux and

Gauss’s law

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Electric field and

flux (existing)

Flux and

Gauss’s law (new)

Gauss’s law

(existing)

Area vector

Relate electric force

to field

Explore the

field of a vertical

charged rod

Test charge

independence

Finding

sign of flux

Electric

field lines

Finding flux in a

non-uniform field

Verify Gauss’s

law consistency

Finding

basic Qenc

Applying

Gauss’s law

Superposition

in Gauss’s law

Area vector

Finding flux signs

and magnitudes

Finding flux in a

non-uniform field

Relate basic Qenc

to independently

found Φnet

Confront difficulties

about non-closed surfaces

(BASED ON SINGH 2006)

Symmetry considerations

(BASED ON SINGH 2006) (To HW)

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Physics

Education

Group

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Difficult for students:1

Flux throughportion of aGaussian surfaceSuperposition and“blocking” of fieldsTutorial helps withthese

1Kanim, S. (1999)

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Difficult for students:1

Flux throughportion of aGaussian surfaceSuperposition and“blocking” of fieldsTutorial helps withthese

Large sheet,

+σo

+q

Added

ΦL

Gaussian

surface

Question: Does ΦL increase,

decrease, or remain the same?1Kanim, S. (1999)

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Impact of changes

10%

30%

50%

Correct

reasoning

Ignored

point charge

Applied Gauss’s

law to end cap

Incorrect

reasoning

Lined: original, N = 238

Solid: modified, N = 302

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With the new Flux and Gauss’s law tutorial:Students were about equally-well preparedReduced class time:We did more the same with less!Made room to cover more topics

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Next steps

Further validation of flux and Gauss’s lawOptimize time spent/condense more tutorials:

Forces & Newton’s second and third lawsLenz’s law & Faraday’s law

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Next steps

+

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Thank you for coming!Acknowledgments:

Grant No. DUE-1022449

Physics

Education

Group

Aziz Khan

Other UWPEGmembers:

Lillian McDermottPeter ShafferPaula HeronDonna MessinaRyan HazeltonPaul EmighAlexis OlshoBert XueTong WanSheh Lit ChangLisa Goodhew

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Exam questionsOlder conceptual question: N = 238

ΦR

Cube

Gaussian

surface d

d

Hollow sphere,

non-conducting

Sphere

Changes

sides

uniform

+ charge

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Exam questionsNewer conceptual question: N = 302

+σo

−qo

Case 1

Gaussian

surface

+4qo

enclosed

+σo

Translated

closer

−qo

ΦL

Case 2

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Exam responsesInitial calculation question (E in thick chargedshell): N = 308

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Exam responsesCorrect explanation

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Exam responses

“Ignored point charge” explanation

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Exam responses

“Applied Gauss’s law” explanation

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