Home Page Textbooks Physics: Principles and Problems Page 678: Section Review

Physics: Principles and Problems

9th Edition

Elliott, Haase, Harper, Herzog, Margaret Zorn, Nelson, Schuler, Zitzewitz

ISBN: 9780078458132

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Page 678: Section Review

Exercise 9

Step 1

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Yes and that is the principle of many induction motors. The only thing that matters is the change of the magnetic flux through the conductor, how it is achieved is the question of secondary importance.

Result

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Yes, it is possible to do so.

Exercise 10

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Wheel rotation is the source of the energy for the bulb. This mechanical energy is transformed to electrical in the lightbulb generator.

Result

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Rotation of the wheel is the source of the energy for the light bulb.

Exercise 11

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When the diaphragm is pushed in, EMF will be generate to compensate for the change in the magnetic flux. The current will therefore run up.

Result

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The current will run up.

Exercise 12

Step 1

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In order to increase the output current frequency one must increase the frequency of the coil itself. In that way the current will oscillate faster.

Result

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One should increase the coil rotation frequency.

Exercise 13

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The electromotive force or the induced voltage is given as

$$
EMF=BLv
$$

So we see that it is directly proportional to the magnetic field. So if we increase the magnetic field, the voltage will increase. Another thing entirely is why does this voltage appear. It is due to the induced current which tries to compensate for the change in magnetic flux by creating a magnetic field of the opposite direction
$I=frac{EMF}{R}$
Therefore, the larger is the magnetic field, the larger is the change in flux and thus the larger is the current needed to oppose it.

Result

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Because larger magnetic fields mean larger changes in magnetic flux.

Exercise 14

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The fundamental principle behind the function of electric generators is the fact that change of the magnetic flux in a closed circuit generates a potential difference known as EMF, i.e. induces electric current.

Result

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The change in magnetic flux generates electric currents.

Exercise 15

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The reason for this is the fact that the power depends on the square of the current i.e. it is given

$$
P=I^2R
$$

This gives that the energy is given as

$$
Delta E=I^2R Delta t
$$

Therefore, the energy cannot be taken from the lamp back to the generator.

Result

2 of 2

The power depends on the square of the current.

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