Electromagnetism Worksheets – Answer completely and/or show K-U-E-S on your own paper
1. In terms of attraction and repulsion, how do negative particles affect negative particles? How do negatives affect positives?
2. How does one coulomb of charge compare with the charge of a single electron?
3. What happens to electrons in any charging process?
4. Give an example of something charged by friction.
5. Give an example of something charged by simple contact.
6. Give an example of something charged by induction.
7. What occurs when we “ground” an object?
8. What is the purpose of a lightning rod?
9. How does an electrically polarized object differ from an electrically charged object?
10. How much energy is given to each coulomb of charge that flows through a 1.5-volt battery?
11. A balloon may be charged to several thousand volts. Does this mean it has several thousand joules of energy? Explain
12. We do not feel the gravitational forces between ourselves and the objects around us because these forces are extremely small. Electrical forces, in comparison, are extremely huge. Since we and the objects around us are composed of charged particles, why don’t we usually feel electrical forces?
13. An electroscope is a simple device consisting of a metal ball that is attached by a conductor to two thin leaves of metal foil protected from air disturbances in a jar, as shown. When a charged body touches the ball, the leaves that normally hang straight down spread apart. Why? (Electroscopes are useful not only as charge detectors, but also for measuring the quantity of charge: the more charge transferred to the ball, the more the leaves diverge.)
14. Strictly speaking, when an object acquires a positive charge by the transfer of electrons, what happens to its mass? When it acquires a negative charge? Think small!
15. How can you charge an object negatively with only the help of a positively charged object?
16. How does the magnitude of electrical force between a pair of charged objects change when the objects are moved twice as far apart? Three times as far apart?
17. How does the magnitude of electric force compare between a pair of charged particles when they are brought to half their original distance of separation? To one- quarter their original distance? To four times their original distance? (What law guides your answers?)
18. Why are metal-spiked shoes not a good idea for golfers on a stormy day?
19. If you are caught outdoors in a thunderstorm, why should you not stand under a tree? Can you think of a   reason why you should not stand with your legs far apart? Or why lying down can be dangerous? (Hint: Consider electric potential difference.)
20. If you rub an inflated balloon against your hair and place it against a door, by what mechanism does it stick? Explain.
21. When the chassis of a car is moved into a painting chamber, a mist of paint is sprayed around the chassis When it is given a sudden electric charge and mist is attracted to it, presto—the car is quickly and uniformly painted. What does the phenomenon of polarization have to do with this?
22. If you put in 10 joules of work to push 1 coulomb of charge against an electric field, what will be its voltage with respect to its starting position? When   what will be its kinetic energy if it flies past its starting released   position?
23. What is the voltage at the location of a 0.0001 C charge that has an electric potential energy of 0.5 J (both measured relative to the same reference point)?
24. What safety is offered by staying inside an automobile during a thunderstorm? Defend your answer.
25. What condition is necessary for the flow of heat? What analogous condition is necessary for the flow of charge?
26. What condition is necessary for the sustained flow of water in a pipe? What analogous condition is necessary for the sustained flow of charge in a wire?
27. What exactly is an ampere?
28. Why is a current-carrying wire normally not electrically charged?
29. Does charge flow through a circuit or into a circuit? Does voltage flow through a circuit, or is voltage established across a circuit?
30. Will water flow more easily through a wide pipe or a narrow pipe? Will current flow more easily through a thick wire or a thin wire?
31. Does heating a metal wire increase or decrease its electrical resistance?
32. If the voltage impressed across a circuit is held constant while the resistance doubles, what change occurs in the current?
33. If the resistance of a circuit remains constant while the voltage across the circuit decreases to half its former value, what change occurs in the current?
34. What is the error in saying that electrons in a common battery driven circuit travel at about the speed of light?
35. What is the error in saying the source of electrons in a circuit is the battery or generator?
36. When you pay your household electric bill at the end of the month, which of the following are you paying for: voltage, current, power, energy?
37. What is an electric circuit?
38. In a circuit of two lamps in series, if the current through one lamp is 1 A, what is the current through the other lamp? Defend your answer.
39. If 6 V are impressed across the above circuit and the voltage across the first lamp is 2 V. what is the voltage across the second lamp? Defend your answer.
40. What is a main shortcoming of a series circuit?
41. In a circuit of two lamps in parallel, if there are 6 V across one lamp. What is the voltage across the other lamp?
42. How does the sum of the currents though the branches of a simple parallel circuit compare to the current that flows through the voltage source?
43. If an electric current flows from one object to another, what can we say about the relative magnitudes of the electric potentials of the two objects?
44. What happens to the brightness of light emitted by a light bulb when the current that flows in it increases?
45. Is a current-carrying wire electrically charged?
46. Your tutor tells you that an ampere and a volt really measure the same thing, and the different terms only serve to make a simple concept seem confusing. Why should you consider getting a different tutor?
47. In which of the circuits below does a current exist to light the bulb?
48. Sometimes you hear someone say that a particular appliance “uses up” electricity. What is it that the appliance actually uses up and what becomes of it?
49. Suppose you leave your car lights on while at a movie. When you return, your battery is too “weak” to start
50. your car. A friend comes and gives you a jump start with his battery and battery cables. What physics occurs when your friend gives you a jump start?
52. Only a small percentage of the electric energy fed into a common light bulb is transformed into light. What happens to the rest?
53. Why are thick wires rather than thin wires usually used to carry large currents?
54. Will a lamp with a thick filament draw more current or less current than a lamp with a thin filament”
55. A 1 mile long copper wire has a resistance of 10 ohms. What will be its new resistance when it is shortened by: (a) cutting it in half; (b) doubling it over and using it as “one” wire?
56. What is the effect on current in a wire if both the voltage across it and its resistance are doubled? If both are halved?
57. Will the current in a light bulb connected to a 220-V source be greater or less than when the same bulb is connected to a 110-V source?
58. Are automobile headlights wired in parallel or in series? What is your evidence?
59. A car’s headlights dissipate 40 W on low beam, and 50 W on high beam. Is there more or less resistance in the high beam filament?
60. To connect a pair of resistors so their equivalent resistance will be more than the resistance of either one, should you connect them in series or in parallel?
61. To connect a pair of resistors so their equivalent resistance will be less than the resistance of either one, should you connect them in series or in parallel?
62. Why is the wingspan of birds a consideration in determining the spacing between parallel wires in a power line?
63. If electrons flow very slowly through a circuit, why does it not take a noticeably long time for a lamp to glow when you turn on a distant switch?
64. If a glowing light bulb is jarred and oxygen leaks inside, the bulb will momentarily brighten considerably before burning out. Putting excess current through a light bulb will also burn it out. What physical change occurs when a light bulb burns out?
65. Consider a pair of flashlight bulbs connected to a battery. Will they glow brighter connected in series or in parallel? Will the battery run down faster if they are connected in series or in parallel?
66. In the circuit shown, how do the brightnesses of the identical lightbulbs compare? Which lightbulb draws the most current? What will happen if bulb “A” is unscrewed? If bulb “C” is unscrewed?
67. Why is there no effect on other branches in a parallel circuit when one branch of the circuit is opened or closed?
68. When a pair of identical resistors are connected in series, which of the following is the same for both resistors: Voltage across each, power dissipated in each, current through each? Do any of your answers change if the resistors are different from each other?
69. When a pair of identical resistors are connected in parallel, which of the following is the same for both resistors: Voltage across each; power dissipated in each; current through each? Do any of your answers change if the resistors are different from each other?
70. Why are devices in household circuits almost never connected in series?
71. Is the resistance of a 100 W bulb greater or less than the resistance of a 60-W bulb? Assuming the filaments in each bulb are of the same length and made material, which bulb has the thicker filament? of the same
72. If a 60 W bulb and a 100 W bulb are connected in series in a circuit, across which bulb will there be the greater voltage drop? How about if they are connected in parallel?
73. The wattage marked on a light bulb is not an inherent property of the bulb but depends on the voltage to which it is connected, usually 110 or 120 V. How many amperes flow through a 60-W bulb connected in a 120-V circuit?
74. A certain device in a 120-V circuit has a current rating of 20 A. What is the resistance of the device (how many ohms)?
75. Find the current drawn by a 1200 W hair dryer connected to120 V. Then using the method you used in the previous problem. Find the resistance of the hair dryer
76. The total charge that an automobile battery can supply without being recharged is given in terms of ampere hours. Atypical 12 V battery has a rating of 60 ampere hours (60 A for 1 h, 30 A for 2 h, and so on). Suppose you forget to turn off the headlights in your parked automobile. If each of the two headlight draws 3 A, how long will it be before your battery is “dead”?
77. How much does it cost to operate a 100 W lamp continuously for I week if the power utility rate is 15 cents/kWh?
78. A 4-W night-light is plugged into a 120-V circuit and operates continuously for 1 year. Find the following: (a) the current it draws, (b) the resistance of its filament, (c) the energy consumed in a year, and (d) the cost of its operation for a year at the utility rate of 15 cents/kWh.
79. A certain light bulb with a resistance of 95 ohms is labeled “150 W.” Was this bulb designed for use in a 120-V circuit or a 220-V circuit?
80. Is the rule for the interaction between magnetic poles similar to the rule for the interaction between electrically charged particles?
81. In what way are magnetic poles very different than electric charges?
82. What produces a magnetic field?
83. What is the difference between an unmagnetized iron nail and a magnetized iron nail?
84. Why will dropping an iron magnet on a hard floor make it a weaker magnet?
85. What happens to the direction of the magnetic field about an electric current when the direction of the current is reversed?
86. Why is the magnetic field strength greater inside a current-carrying loop of wire than about a straight section of wire?
87. How does a galvanometer detect electric current?
88. What is a galvanometer called when calibrated to read current? To read voltage?
89. What is the evidence for the Earth being a big magnet?
90. In what sense are all magnets electromagnets?
91. Why is it inadvisable to make a horseshoe magnet from a flexible material?
92. What surrounds a stationary electric charge? a moving electric charge?
93. “An electron always experiences a force in an electric field, but not always in a magnetic field.” Defend this statement.
94. Why will a magnet attract an ordinary nail or paper clip, but not a wooden pencil?
95. Will either pole of a magnet attract a paper clip? Ex plain what is happening inside the attracted paper clip,
96. The north pole of a compass is attracted to the north pole of the Earth, yet like poles repel. Can you resolve this apparent dilemma?
97. Cans of food in your kitchen pantry are likely magnetized. Why?
98. Your friend says that when a compass is taken across the equator, it turns around and points in the opposite direction. Your other friend says this is not true, that southern-hemisphere types use the south pole of the compass to point toward the nearest pole. You’re on; what do you say?
99. Magnet A has twice the magnetic field strength of magnet B (at equal distance) and at a certain distance pulls on magnet B with a force of 50 N. With how much force, then, does magnet B pull on magnet A?
100. A magnet exerts a force on a current-carrying wire. Does a current-carrying wire exert a force on a magnet? Why or why not?
101. To make a compass, point an ordinary iron nail along the direction of the Earth’s magnetic field (which, in the northern hemisphere, is angled downward as well as northward) and repeatedly beat on it for a few seconds with a hammer or a rock. Then suspend it at its center of gravity by a string. Now it’s a compass. Why does the beating magnetize the nail?
102. Inside a laboratory room there is said to be either an electric field or a magnetic field, but not both. What experiments might be performed to determine what kind of field is in the room?
103. If you had two bars of iron, one magnetized and the other not, and no other materials at hand, how could you tell which bar was the magnet?
104. Why is it more difficult to thrust a magnet into a coil of many loops compared with a single loop?
105. What must change in order for electromagnetic induction to occur?
106. What are the three ways that voltage can be induced in a wire?
107. How does the frequency of induced voltage compare to how frequently a magnet is plunged in and out of a coil of wire?
108. Why does a generator produce alternating current?
109. Electric energy can certainly be carried along wires, but can it be carried across empty space? If so, how?
110. Why does a transformer require alternating current?
111. If a transformer is efficient enough, can it step up energy? Explain.
112. What is the principal advantage of AC over DC
113. Why is power transmitted at high voltages over long distances?
114. A common pickup for an electric guitar consists of a coil of wire around a small permanent magnet. The magnetic field of the magnet induces magnetic poles in the nearby guitar string. When the string is plucked, the rhythmic oscillations of the string produce the same rhythmic changes in the magnetic field through the coil, which in turn induce the same rhythmic voltages in the coil, which when amplified and sent to a speaker produce music! Why will this type of pickup not work with nylon strings?
115. Why is a generator shaft harder to rotate when it is connected to a circuit and supplying electric current?
116. If your metal car moves over a wide, closed loop of wire embedded in a road surface, will the magnetic field of the Earth within the loop be altered? Will this produce a pulse of electric current? Can you think of a practical application for this at a traffic intersection?
117. At the security area of an airport, you walk through a weak AC magnetic field inside a coil of wire. What is the result of a small piece of metal on your person that slightly alters the magnetic field in the coil?
118. A piece of plastic tape coated with iron oxide is magnetized more in some parts than in others. When the tape is moved past a small coil of wire, what happens in the coil? What is a practical application of this?
119. What is the primary difference between an electric motor, and an electric generator?
120. Your friend says that if you crank the shaft of a DC motor manually, the motor becomes a DC generator. Do you agree or disagree?
121. A magician places an aluminum ring on a table, underneath which is hidden an electromagnet. When the magician says “abracadabra” (and pushes a switch that starts current flowing through the coil under the table), the ring jumps into the air. Explain his “trick.”
122. How could a light bulb near, yet not touching, an electromagnet be lit? Is AC or DC required? Defend your answer.
123. Two separate but similar coils of wire are mounted close to each other, as shown below. The first coil is connected to a battery and has a direct current flowing through it. The second coil is connected to a galvanometer. How does the galvanometer respond when the switch in the first circuit is closed? After being closed when the current is steady? When the switch is opened?
124. How does the current in the secondary of a transformer compare with the current in the primary when the secondary voltage is twice the primary voltage?
125. In what sense can a transformer be thought of as an electrical lever? What does it multiply? What does it not multiply?
126. Why can a hum usually be heard when a transformer is operating?
127. What does an incident radio wave do to the electrons in a receiving antenna?
128. An ideal transformer has 50 turns in its primary coil and 250 turns in its secondary coil. Twelve volts AC is connected to the primary coil. Find: (a) volts AC available at the secondary coil; (b) current in a 10 W device connected to the secondary coil; (c) power supplied to the primary coil.
129. A model electric train requires 6 V to operate. If the primary coil of its transformer has 240 turns, how many turn should the secondary have? The primary coil is connected to a 120 V household circuit.