physics labs with flavor

1 Copyright 2010 M. AGREST

Physics labs with flavor

Physics and Astronomy Department

College of Charleston,Charleston, SC

Charleston, SCOctober 23, 2010.

Southern Atlantic Coast Section American Association of Physics Teachers

Workshop for Physics and Physical Science Teachers


Recurrent learning in Physics Labs

Abstract: The principle of recurrent studies as a way to bring flavor into Introductory Physics labs was discussed earlier 1,2. Participants will get some hands-on experience of Recurrent Studies and feel excitement due to the flavor it brings into the introductory Physics Labs You will perform forward study of a phenomenon and calculate unknown parameters based on your own measurements and assumptions. After discussion you will set up the backward study. The purpose of it is to evaluate how accurate was your result in the direct study. Here the parameter of interest in forward study stays unchanged, but others will change. Based on your measurements of some of them and the result of the forward study, you have to predict one (or more) parameters.Then you will perform the backward experiment to measure the value of the predicted parameter and calculate the percent error for your prediction. We expect that you will experience excitement (as students have) and you will be motivated to try the recurrent studies method for innovation of your teaching.1. M.M. Agrest, “Physics labs with flavor,” Phys. Teach. 47, 297 (May2009)2. M.M. Agrest, “Physics labs with flavor II,” Phys. Teach. (in print for 2011)

SACS AAPT Physics Labs with Flavor Mikhail M. AgrestFall 2010 Recurrent studies.


1. Forward study Students study the phenomenon, perform the experiments, analyze the data and make conclusions about the results. find a quantity as a feature of the phenomenon

/Based on theoretical model, the measurement results, statistics, etc/2. Backward study

New assignment; Based on the results in 1. find the quantity of a questioned parameter.

3. Shoot for your grade Perform the new experiment in the presence of the instructor Compare the results with the prediction Get your Grade

Shoot for your grade General Idea



Momentum & Energy 1

V0

x-x0

y-y0

0

00

0

00

2

0

00

2

22

yy

gxxV

g

yyt

t

xxV

tgyy

tVxx

2

2

2

2

2

1

2

1

)(00)(2

1)()0(

m

mM

mmM

mM

mMbm

VMm

m

gH

Vg

H

VMm

mV

gHMmVMm

MmVmV

V0 M

m

H

M+m

Kinematics



Momentum & Energy 2

V0 M

m

M+m

H

(mVm 0)b VmM (m M)12

(m M) VmM 2 0 0 (m M)gH

Vm m M

mVmM

VmM 2gH Vm

m Mm

2gH

2

2

2

2

2

1

2

1

)(00)(2

1)()0(

m

mM

mmM

mM

mMbm

VMm

m

gH

Vg

H

VMm

mV

gHMmVMm

MmVmV

V0 M

m

H

M+m

Kinematics



x-x0

hH

Bernoulli

Fluid Mechanics



Bernoulli2

x-x0

hH

kv

v

h

gxxv

g

ht

t

xxv

gth

vtxxgt

tVyy

tVxx

th

y

x

exp

0exp

0

20

2

00

00

2

222

hH

x-x0

)(22

)(2

2

2

)(2

0

02

0

hHhkg

hhHgkxx

g

ht

vtxx

gth

vtxx

hHgkkvv th

Fluid Mechanics



Reflection and Refraction

1.00i airn n

Snell’s Law

sin sini i t tn n

sin

sini

glass it

n n

1 2

1 2

1 1

1 2 180

1 2 180

sin sin

t i

t i

airt i

prism

n

n

it 2i

2t

1 2

Determine Index of Refraction



Total Internal reflection

1 2

1 2 1 2

2 2

12

1 1

1 2 180

1 2 180

1

1sin sin

1sin 2

sin sin

t i

t i t i

airi t

prism prism

iprism

prismi t

air

n

n n

n

n

n

2 90t

it 2i

1 2



Focal Length of a Converging Lens

F

F

1

f

1

si

1

so

## so sif fave

1

2

3

…..

N

Backward study Assignment:

Based on your result for the focal length f for a given So predict Si

Forward study

Optics



Focal Length of a diverging Lens

1

f1

1

si1

1

so11f2

1si2

1so2

so2 d si1

1

f1

1

f2

1

f12

F

F

# so sif fave

1

2

3

…..

N

Backward study Assignment:

Based on your result for the focal length f predict Si for a given So

AForward study

Optics



INTERFERENCE

y

L

Laser

m b sin;

sin yL

b y

mL

2 2

2 2

sin ;

sin

sin

m d

y

L y

m md L y

y

Waves of Light

y

L

Laser



3R

4R

5R

Fig. 1a

V4

1R

2R

V

Fig. 1b

V9

R7R6

R10

V

R8

R9

The forward study. Finding voltage of the power source. Terminals of one of the resistors (let us say resistor R4) in the circuit are accessible, so students can measure the difference of potentials (V4) across

this resistor. Based on the measurement of the voltage, students have to calculate the voltage V of the power source. The experiment is repeated several times as follows: Replacing this resistor by a different resistor, students calculate the voltage of the power source several times and estimate the error of their results.

Backward study. Finding voltage across the test resistor. The test circuit (Fig.1b) consists of the same power source providing the same value of the voltage as in the forward study to a different circuit. The assignment is: calculate the voltage drop across one of the resistors based on the experimental value of the voltage supplied. The test circuit can be completely different or it can be the same one with the replaced testing resistor.

Experimental assessment. Comparing the results. After the “predicted” voltage is announced, the measurement should be performed and the answer is announced. Usually this event attracts students from all other groups of the lab as it is accompanied with shouts “Hurrah”, “Yes!” and other expression of satisfaction. The grade for this part of the lab should be based on the percent error in the predicted value of voltage.

Resistors in a circuit

Electricity



3R

4R

5R

Fig. 1a

V4

1R

2R

V

Fig. 1b

V9

R7R6

R10

V

R8

R9


• Construct a circuit according the diagram 1.Here: R1=2 k R2=6.5 k R3=5.5 kR4=1.5 kR5=4.5 k•Using a voltmeter, measure V4, • based on the measured V4 calculate V of the power source.

• Construct a circuit according the diagram 2.Here: R6=4 k R7=3.5 k R8=2.5 kR9=5.5 kR10=1.5 k•Using the calculated value of V from part 1, calculate V9. measure V4, • based on the measured V4 calculate V of the power source.

Electricity




Construct a circuit according the diagram 1.Here: R1=2 k R2=6.5 k R3=5.5 kR4=1.5 kR5=4.5 kInstructor will set the variable power source at Voltage V unknown to you.Using a voltmeter measure V4, based on the measured V4 determine V of the power source.When the same resistors arranged with this power source into another circuit, find voltage drop V4 across its resistor R4

diagram 2

1R

2R

3R

4R

5R

V

diagram 1

4VR2

R4

R1

R5

V

R3

4V

Electricity



Speed of Sound in the AirAssignment 1Given: Tuning fork with a given frequency f.

Find: Speed of Sound in the air. vsound T

f

L1 1

4

L2 3

4

L3 5

4

fv fsoundf 3213

1

Assignment 2: Result from the Assignment 1:

Find frequency of “unknown” (test) tuning fork.Measure: at resonance to find as in (1);Then find

iL

soundv

f Assignment 2Alternative: Use result from the Assignment 1: Set where you expect the resonance based on given frequency f of the test tuning fork.Compare the with one which lets you get the loudest Woo…ooo…ooo

vsound T

f

iLiL

4

5L

WavesSACS AAPT Physics Labs with Flavor Mikhail M. AgrestFall 2010 Recurrent studies.


The END

Visual assessment of students’ prediction of the results emotionally involves them and makes the learning process more effective, brings popularity into the discipline because it involves hands-on experience, using and testing the students’ results during their lab work.

physics labs with flavor

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