Q&A Hero

Q: When we say an appliance "uses up" electricity, we are actually saying that A) current disappears. B) electric charges are dissipated. C) the main power supply voltage is lowered. D) electrons are taken out of the circuit and put somewhere else. E) electrical energy changes to thermal energy.

Q: In a circuit powered by a battery it is correct to say that electrons flow A) from the battery and into the circuit. B) from the negative terminal to the positive terminal of the battery. C) through both the battery and the devices making up the circuit. D) none of the above

Q: When you purchase a water pipe in a hardware store, water is not included. When you purchase copper wire, electrons A) must be supplied by you, just as water in a water pipe. B) already exist in the wire. C) may fall out, which is why wires are insulated. D) none of the above

Q: The number of electrons delivered daily by power utilities to an average American home during a typical week is A) zero. B) 110. C) 220. D) billions of billions. E) none of the above

Q: The origin of the glow from the filament inside the ac incandescent lamp in your bedroom is A) electrons resupplied by the wall outlet. B) electrons already in the filament. C) the positive charges that flow in the filament. D) resistance in the filament.

Q: The average speed of electrons flowing though the filament of a dc flashlight bulb is A) about the same speed as sound in metals. B) dependent on how quickly electrons bumps into one another. C) the speed of light. D) 1000 cm/s. E) a snail's pace of less than 1 cm/s.

Q: In a common dc circuit, electrons typically move at the speed of A) a fraction of a centimeter per second. B) a few meters per second. C) sound. D) light. E) none of the above

Q: The source of electrons lighting an incandescent ac light bulb is A) the power company. B) the electric outlet. C) atoms in the light-bulb filament. D) the wire leading to the lamp. E) the source voltage.

Q: The source of electrons in an ordinary electric circuit is A) a dry cell, wet cell, or battery. B) usually a wall socket. C) a generator at the power station. D) the electric conductor itself. E) none of the above

Q: Current that is typically 60 hertz is A) direct current. B) alternating current. C) either of these D) neither of these

Q: Alternating current is normally produced by a A) battery. B) generator. C) both of these D) neither of these

Q: Direct current is normally produced by a A) battery. B) generator. C) both of these D) neither of these

Q: To say a circuit is dc is to say that current in the circuit A) has a single direction. B) alternates only slowly. C) is parallel to the connecting wires.

Q: The electric field in the wires of an ac circuit A) changes via the inverse square law. B) changes direction with time. C) remains relatively constant. D) is nonexistent. E) none of the above

Q: A coulomb of charge flowing in a bulb filament powered by a 6-volt battery is provided with A) 6 ohms. B) 6 amperes. C) 6 joules. D) 6 watts. E) 6 newtons.

Q: A coulomb of charge passing through a 6-V battery acquires A) 6 joules. B) 6 amperes. C) 6 ohms. D) 6 watts. E) 6 newtons.

Q: The net electric charge on a current-carrying wire is normally A) zero. B) equal and opposite to the charge within the wire. C) the voltage divided by the resistance.

Q: An ampere is a unit of electric A) pressure. B) current. C) resistance. D) all of the above E) none of the above

Q: The electric current in a copper wire is normally composed of A) electrons. B) protons. C) ions. D) all of the above

Q: The flow of electrons in an electric circuit move by A) bumping other electrons. B) colliding with molecules. C) interacting with an established electric field. D) none of the above

Q: Electric charge will flow in an electric circuit when A) electric resistance is low. B) a potential difference exists. C) the circuit is grounded. D) electric devices in the circuit are not defective.

Q: When we think of electric potential difference, we are thinking about A) current. B) voltage. C) resistance.

Q: Just as a sustained flow of water in a hydraulic circuit needs a pump, the flow of charge in an electric circuit needs A) current. B) voltage. C) resistance.

Q: Electrons flow in a wire when there is A) an imbalance of charges in the wire. B) a potential difference across its ends. C) a difference in potential energy across its ends. D) none of the above

Q: The amount of energy given to each coulomb of charge flowing through a 12-V battery is A) 12 J. B) 12 A. C) 12 V. D) all of the above E) none of the above

Q: A suitable electric pump in an electric circuit is a A) chemical battery. B) generator. C) both of these D) neither of these

Q: A sustained flow of electric charge requires A) a potential difference. B) a resistance. C) an electric field. D) electric polarization.

Q: A sustained electric current can be achieved with a A) generator. B) battery. C) both D) none of the above

Q: The purpose of a voltage source is to provide an electrical A) energy sink. B) field. C) pressure.

Q: The flow of charge in a circuit depends on A) adequate resistance. B) a potential difference. C) adequate chemical action. D) all of the above

Q: Just as water flows from high to low pressure, electric charge flows from A) high to low voltage. B) high charge concentration to low charge concentration. C) high resistance to low resistance. D) all of the above E) none of the above

Q: A term for electric pressure is A) current. B) voltage. C) electric resistance.

Q: Voltage is most similar to A) pressure. B) current. C) resistance. D) all of the above E) none of the above

Q: Lillian safely touches a 100,000-volt Van de Graaff generator. Although the voltage is high, the relatively small amount of charge means a relatively small amount of A) energy transfer. B) electric field. C) polarization. D) conduction.

Q: The photo on page 193 shows Lillian's hair standing out when her hand is on a charged Van de Graaff generator, which illustrates A) strands of hair become charged and repel one another. B) a high voltage is communicated to strands of hair. C) strands of hair orient themselves in an electric field. D) the effect of electrons and protons deposited on her hair.

Q: The different outcomes in touching a faulty 120-V light fixture and a high-voltage Van de Graaff generator have to do with differences in A) sustainability of charge flow. B) duration of charge flow. C) amount of energy transferred. D) all of the above E) none of the above

Q: Which is more dangerous, touching a faulty 120-V light fixture, or a Van de Graaff generator charged to 100,000 V? A) light fixture B) generator C) both equally

Q: Normally a balloon charged to several thousand volts has a relatively small amount of A) charge. B) energy. C) both of these D) none of the above

Q: A charged balloon illustrates that something can have a great amount of A) potential energy and a low voltage. B) voltage and a small potential energy. C) both voltage and potential energy. D) none of the above

Q: When a battery does 24 J of work on 10 C of charge, the voltage it supplies is A) 2.4 V. B) 4.2 V. C) 24 V. D) 240 V. E) none of the above

Q: An electron is pushed into an electric field where it acquires a 1-V electrical potential. If two electrons are pushed the same distance into the same electric field, the electrical potential of the two electrons is A) 0.25 V. B) 0.5 V. C) 1 V. D) 2 V. E) 4 V.

Q: It takes 10 J of work to push a charge initially at rest into an electric field. If the charge is then released, it flies back to its initial position with a kinetic energy of A) zero. B) 5 J. C) 10 J. D) more than 10 J. E) need more information.

Q: It takes 10 J of work to push a charge into an electric field. Relative to its starting position it has gained a potential energy of A) less than 10 J. B) 10 J. C) more than 10 J. D) none of the above

Q: If you do 10 J of work to push 1 coulomb of charge into an electric field, its voltage with respect to its starting position is A) less than 10 V. B) 10 V. C) more than 10 V. D) none of the above

Q: Electric potential is the ratio of electric energy to the amount of electric A) current. B) resistance. C) charge. D) voltage. E) none of the above

Q: Electric potential is measured in units of A) volts. B) joules. C) amperes. D) watts. E) any or all of these

Q: Food cooked in a microwave oven depends on electrical A) conduction. B) charge polarization. C) resistance changes. D) field strength. E) all of the above

Q: Electric charge distributes itself on conducting surfaces A) with greater concentration on flat parts. B) such that the electric field inside is zero. C) both of the above D) none of the above

Q: Much of the charge on a conducting cube is A) uniformly spread over its surface. B) partly beneath the surface. C) mutually repelled toward its corners. D) none of the above

Q: The electric field lines between a pair of equal and opposite charges are A) directed from positive to negative. B) more concentrated closer to the charges. C) vectors, with patterns resulting from the inverse-square law. D) all of the above E) none of the above

Q: A proton and an electron placed in an electric field experience the same force. Which undergoes the greater acceleration? A) electron B) proton C) both equally D) none of the above

Q: The electric field between oppositely-charged parallel plates is A) uniform. B) stronger at the ends. C) composed of field lines curved in opposite directions. D) none of the above

Q: The electric field around an isolated electron has a certain strength at a 1-cm distance from the electron. The electric field strength 2 cm from the electron is A) half as much. B) the same. C) twice as much. D) four times as much. E) none of the above

Q: Every proton in the universe is surrounded by its own A) electric field. B) gravitational field. C) both of these D) none of the above

Q: Electric field lines about a point charge extend A) outward when the charge is negative. B) outward when the charge is positive. C) in circles.

Q: The direction of an electric field is defined as the direction of force on A) a positively-charged particle. B) a negatively-charged particle. C) any charged particle.

Q: Two charged particles near each other are released. As the particles move, the velocity of each increases. Therefore, the particles have A) the same sign. B) the opposite sign. C) not enough information

Q: Two charged particles near each other are released. As they move, the force on each particle increases. Therefore, the particles have A) the same sign. B) the opposite sign. C) not enough information

Q: A positive and a negative charge near each other are released. As they move, the force on each particle A) increases. B) decreases. C) stays the same.

Q: A negatively-charged balloon touching a wooden wall A) pulls positive charge on the wall surface toward it. B) pushes negative charge in the wall away from it. C) polarizes molecules in the wall. D) all of the above E) none of the above

Q: A balloon will stick to a wooden wall if the balloon is charged A) negatively. B) positively. C) either of these D) none of the above

Q: An electrically polarized object normally has A) a net charge of zero. B) displaced charges. C) both of these D) none of the above

Q: To say that an object is electrically polarized is to say A) it is electrically charged. B) its charges have been rearranged. C) its internal electric field is zero. D) it is only partially conducting. E) it is to some degree magnetic.

Q: Two charged particles repel each other with a force F. If the charge of one particle is doubled and the distance between them is doubled, the force will be A) F. B) 2 F. C) F/2. D) F/4. E) none of the above

Q: Two charged particles 1 m apart exert a 1-N force on each other. If the particles are instead 0.5 m apart, the force on each particle will be A) 1.0 N. B) 2.0 N. C) 4.0 N. D) 8.0 N. E) 16.0 N.

Q: Two charged particles 1 m apart exert a 1-N force on each other. If the particles are instead 0.25-m apart, the force on each particle will be A) 1.0 N. B) 2.0 N. C) 4.0 N. D) 8.0 N. E) 16.0 N.

Q: Two charged particles 1 m apart exert a 1-N force on each other. If the magnitude of each charge is doubled, the force on each particle will be A) 1 N. B) 2 N. C) 4 N. D) 8 N. E) none of the above

Q: When the distance between two charges is halved, the electric force between the charges A) quadruples. B) doubles. C) is half. D) is reduced by one-quarter. E) none of the above

Q: If electrons were positive and protons were negative, Coulomb's law would be written A) the same. B) somewhat differently. C) very differently.

Q: The electric force between charges is strongest when the charges are A) close together. B) far apart. C) either of these

Q: The electric force between charges depends on the A) magnitude of electric charges. B) separation distance between electric charges. C) both of these D) none of the above

Q: A difference between electric and gravitational forces is that electric forces include A) separation distance. B) repulsive interactions. C) the inverse-square law. D) infinite range. E) none of the above

Q: A main difference between gravitational and electric forces is that electric forces A) attract. B) repel or attract. C) obey the inverse-square law. D) act over shorter distances. E) are weaker.

Q: The unit of electric charge, the coulomb, is the charge on A) one electron. B) one proton. C) a specific large number of electrons.

Q: Why is a steam burn more damaging than a burn by boiling water of the same temperature?

Q: Why does a hot dog pant?

Q: From a molecular point of view, explain why evaporation is a cooling process. What cools?

Q: Why does a good emitter of heat radiation appear black at room temperature?

Q: On sunny days, why do hot-air balloons suddenly rise when they drift over a wide road or a black asphalt parking lot?

Q: Explain why white clothing keeps us cool, whereas black clothing warms us. Which is the better reflector? Which is the better absorber?