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What reasons might there be for the universal belief among scientists that there are only two kinds of electric charge? |
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2 | |
Electricity was once thought to be a weightless fluid, an excess of which was "positive" and a deficiency of which was "negative." What phenomena can this hypothesis still explain? What phenomena can it not explain? |
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3 | |
Are electrons or protons easier to remove from an atom? |
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4 | |
Why does the production of electricity by friction always yield equal amounts of positive and negative charge? |
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5 | |
Is there any distance at which the gravitational force between two electrons is greater than the electric force between them? |
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6 | |
Nearly all the mass of an atom is concentrated in its nucleus. Where is its charge located? |
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7 | |
(a) List the similarities and differences between electric and gravitational fields. (b) How could you distinguish experimentally between an electric field and a gravitational field? |
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8 | |
How do we know that the force holding the earth in its orbit about the sun is not an electric force, since both gravitational and electric forces vary inversely with the square of the distance between centers of force? |
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9 | |
When two objects attract each other electrically, must both of them be charged? When two objects repel each other electrically, must both of them be charged? |
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10 | |
A person can be electrocuted while taking a bath if he or she touches a poorly insulated light switch. Why is the electric shock received under these conditions so much more dangerous than usual? |
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11 | |
Name several conductors and insulators of electricity. How well do these substances conduct heat? What general relationship between the ability to conduct heat and the ability to conduct electricity could you infer from this information? |
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12 | |
How is the movement of electricity through air different from its movement through a copper wire? |
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13 | |
Why are two wires used to carry electric current instead of a single one? |
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14 | |
Why do you think bending a wire does not affect its electrical resistance, even though a bent pipe offers more resistance to the flow of water than a straight one? |
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15 | |
An electrical appliance is sometimes said to "use up" electricity. What does it actually use in its operation? |
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16 | |
What aspect of superconductivity has prevented its large-scale application thus far? |
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17 | |
A fuse prevents more than a certain amount of current from flowing in a particular circuit. What might happen if too much current were to flow? What determines how much is too much? |
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18 | |
Heavy users of electric power, such as large electric stoves and clothes dryers, are sometimes designed to operate on 240 V rather than 120 V. What advantage do you think the higher voltage has in these applications? |
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19 | |
Why is a piece of iron attracted to either pole of a magnet? |
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20 | |
The magnetic poles of the earth are called geomagnetic poles. Is the north geomagnetic pole a north magnetic pole or a south magnetic pole? |
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21 | |
Explain why lines of force can never cross one another. |
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22 | |
A physicist is equipped to measure electric, magnetic, and gravitational fields. Which will she detect when a proton moves past her? When she moves past a proton? |
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23 | |
Figure 5-40 shows a current-carrying wire and a compass. In which direction will the compass needle point? |
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24 | |
A current flows west through a power line. Find the directions of the magnetic field above and below the power line; ignore the earth's magnetic field. |
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25 | |
A current-carrying wire is in a magnetic field. What angle should the wire make with the direction of the field for the force on it to be zero? What should the angle be for the force to be a maximum? |
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26 | |
A length of copper wire AB rests across a pair of parallel copper wires that are connected to a battery through a switch, as in Fig. 5-41. The arrangement is placed between the poles of a magnet and the switch is closed. In what direction does the wire AB move? |
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27 | |
When a wire loop is rotated in a magnetic field, the direction of the current induced in the loop reverses itself twice per rotation. Why? |
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28 | |
A beam of protons, at first moving slowly, is accelerated to higher and higher speeds. When the protons are moving slowly, the beam spreads out, but when they are moving fast, the beam diameter decreases. What do you think is the reason for this behavior? |
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29 | |
The following are three basic electromagnetic phenomena: (a) a magnetic field is produced by an electric current; (b) a current-carrying wire experiences a force in a magnetic field (unless aligned with the field); (c) a current is induced in a wire that moves across a magnetic field (or when the field moves across the wire). Which of these phenomena is involved in the operation of the following devices: electric motor, generator, transformer, tape recording head, tape playback head? |
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30 | |
Would you expect to find direct or alternating current in (a) the filament of a lightbulb in your home? (b) the filament of a lightbulb in a car? (c) the secondary coil of a transformer? (d) the output of a battery charger? (e) an electromagnet? |
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31 | |
What acts on the secondary winding of a transformer to cause an alternating voltage to occur across its ends even though the primary and secondary windings are not connected? |
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32 | |
Given a coil of wire and a small lightbulb, how can you tell whether the current in another coil is direct or alternating without touching the second coil or its connecting wires? |
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33 | |
What would happen if the primary winding of a transformer were connected to a battery? |
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