motor lab writeup

8/12/2019 Motor Lab Writeup

1/4

Kimberly Dauber

3/18/2014

Data Collection of Motor

Time (s) Potential (V)

5 4.363858

5.01 4.920635

5.02 3.4065935.03 1.789988

5.04 2.698413

5.05 4.168498

5.06 5.555556

5.07 4.529915

5.08 2.932845

5.09 2.644689

5.1 4.344322

5.11 4.598291

5.12 4.378515.13 2.625153

5.14 2.815629

5.15 4.227106

5.16 5.350427

5.17 4.510379

5.18 2.869353

5.19 2.742369

5.2 4.349206

5.21 5.159951

5.22 4.275946

5.23 2.923077

5.24 2.757021

5.25 2.058608

5.26 1.316239

5.27 4.735043

5.28 1.487179

5.29 2.737485

5.3 4.422466

5.31 5.457875

5.32 4.769231

5.33 2.981685

5.34 1.350427

5.35 3.372405

5.36 4.974359

5.37 4.993895

5.38 3.040293

5.39 2.771673

5.4 4.070818

5.41 5.68254

Time (s) Potential (V)

5.42 4.9157515.43 2.669109

5.44 2.796093

5.45 4.070818

5.46 5.452991

5.47 1.013431

5.48 2.503053

5.49 2.849817

5.5 4.261294

5.51 5.619048

5.52 4.7155075.53 2.595849

5.54 2.610501

5.55 4.373626

5.56 5.106227

5.57 4.647131

5.58 2.898657

5.59 2.595849

5.6 4.334554

5.61 6.351648

5.62 4.866911

5.63 2.888889

5.64 2.483516

5.65 4.505495

5.66 5.526252

5.67 4.100122

5.68 3.118437

5.69 2.893773

5.7 4.422466

5.71 5.916972

5.72 4.798535

5.73 2.815629

5.74 2.766789

5.75 4.080586

5.76 4.114774

5.77 5.428571

5.78 2.815629

5.79 2.810745

5.8 4.40293

5.81 5.150183

5.82 5.286935

5.83 2.986569Time (s) Potential (V)

5.84 2.800977

5.85 4.466422

5.86 5.345543

5.87 4.710623

5.88 2.835165

5.89 2.3663

5.9 4.383394

5.91 5.7558

5.92 5.1208795.93 3.289377

5.94 2.874237

5.95 4.886447

5.96 1.814408

5.97 5.164835

5.98 3.074481

5.99 2.864469

6 4.935287


2/4

Kimberly Dauber

3/18/2014

Graph of Potential vs. Time (with best fit curve)

This graph shows one second of the motor running. The motor completed 21 cycles in the second, yielding an angular velocity of 21 Hertz.

The mathematical model of the motors motion based on the sine curve of best fit is given by


3/4

Kimberly Dauber

3/18/2014

Analysis--

The equation we developed in class for the motion of a motor was given by

From the graph of the motors motion, we know that

We can assume that and that area

The mean induced emf was .

Since the average value of over one second is This allows us to solve for the

average magnetic field of the magnets during this time.

Interestingly, the average magnetic field of the Earth ranges from about 25 to 65 microtesla, much

smaller than the magnetic field of the permanent magnets used. Since the permanent magnetic fields

have such a comparatively large magnetic field, the magnetic field of the Earth has only a negligible

effect on the motor.


4/4

Kimberly Dauber

3/18/2014

Conclusion

An electric motor (which can also be considered a generator) works because according to Faradays Law,

the principles that a changing electric field creates a changing magnetic field and vice versa. There must

be a permanent magnetic field present, the two magnets on the sides of the armature in our case. To

start with, when current runs through the wire around the armature, the loops act as a solenoid and themagnetic field created by the solenoid interacts with the permanent magnetic field to make the

armature turn around its shaft.

Once the armatures magnetic field lined up with the permanent magnetic field, it would seem that the

motor should stop turning. However, the motor is designed with a commutator (possibly a split-ring

commutator) such that after, in this case, one third of a turn, the current in the armature reverses

direction. This creates a magnetic field in the opposite direction as before, forcing the motor to continue

turning in the same direction. As the motor continues to turn, the process repeats rapidly as long as

power is supplied to the armature.

Motors also generate a back current against the emf that makes them run. Because the armature is

rotating, the magnetic flux through the coils is changing. Thus, according to Faradays Law of Induction,

there is an induced emf in the coils that opposes the original voltage. (This is where they dynamo acts as

a generator.) As a result, motors become mainly free spinning, with very little force actually acting on

them due to the magnetic fields, unless a load is placed on them.

Reflection

This years motor lab was much easier than last years motor lab. I rather liked that we did not have to

assemble the motors from scratch, since we had all done that already in Honors Physics or AP Physics B.

It was much more rewarding to spend time analyzing with Logger Pro and such. Ive already spent half

an hour winding coils of wire around a tiny armature; once is enough. Motors are a great way to learn

and review Faradays and Lenzs Laws. Its impossible to understand how a dynamo works without an

understanding of those vital principles. My advice is to keep this lab just the way it is for next year.

motor lab writeup

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