Deck 10: Electricity

Question 1

You and a friend are spending the weekend making up missed lab experiments. You are on to second - semester material and are studying the electrostatic interaction of two charges. You notice that two charges are exerting a certain force on one another. If the distance between two electric charges doubles, then the force they exert on each other changes by how much?

A) 4 times as large
B) 2 times as large
C) ½ as large
D) ¼ as large

Answer 1

¼ as large

Question 2

You and a friend are spending the weekend making up missed lab experiments. You are on to second - semester material and are studying the electrostatic interaction of two charges. You notice that two charges are exerting a certain force on one another. If the distance between two electric charges becomes 1/3 of what it originally was, then the force they exert on each other changes by how much?

A) 9 times as big
B) 3 times as big
C) 1/3 as big
D) 1/9 as big

Answer 2

9 times as big

Question 3

A positive charge and a negative charge will

A) attract each other.
B) repel each other.
C) attract or repel, depending on circumstances.
D) neither attract nor repel.

Answer 3

attract each other.

Question 4

You and a friend are spending a weekend at a carnival. You get bored and begin to make electrostatics measurements. It turns out that you have a charge of +3 Coulombs and your friend a charge of -5 Coulombs. What is the net electric charge?

A) +2 Coulombs
B) -2 Coulombs
C) +8 Coulombs
D) -8 Coulombs

Question 5

Who originally named electric charges as positive and negative?

A) Charles Augustin de Coulomb
B) Andre Marie Ampere
C) Michael Faraday
D) Benjamin Franklin

Question 6

You stick two pieces of adhesive tape on a glass window and then pull them off suddenly. If you now hold the tape pieces near each other, they will be

A) repelled because they have like charges.
B) repelled because they have opposite charges.
C) attracted because they have like charges.
D) attracted because they have opposite charges.

Question 7

Which of the following can cause a charged particle to accelerate?

A) An electric field
B) A gravitational field
C) A neutron field
D) (A) and (B)

Question 8

If an electron and a proton both experience the same electric force,

A) the proton will have greater acceleration.
B) the electron will have greater acceleration.
C) their accelerations will have the same magnitude.
D) neither will accelerate.

Question 9

After running a plastic comb through you hair several times you hold it above a small scrap of paper. The paper jumps off the table and sticks to the comb because the paper becomes

A) magnetic.
B) electrically charged.
C) conducting.
D) electrically polarized.

Question 10

You have just pulled your clothes from the dryer and find that a sock is clinging to your jeans with static electricity. You hold the jeans in one hand and the sock in the other and pull the two apart. As jeans and sock move apart, the forces between them become weaker because the

A) electric charge on each garment increases as they move apart.
B) electric current passing through each garment diminishes as they move apart.
C) electric charge on each garment diminishes as they move apart.
D) distance between the garments increase.

Question 11

A charged object is able to attract

A) only charged objects
B) neutral objects and neutral particles
C) neutral objects but not neutral particles
D) only neutral particles

Question 12

Suppose you have two identical socks that exert a force of 10 N on each other. Now you move them so they are three times as far apart as they were originally.
-Calculate the new force between the objects.

Question 13

Suppose you have two identical socks that exert a force of 10 N on each other. Now you move them so they are three times as far apart as they were originally.
-Will this force be attractive or repulsive? Please explain.

Question 14

Your instructor staggers into class after a classic party. He does a demonstration in class where he measures a force of attraction between two positively charged spheres to be 12N when they are 5m apart and then claims that the force is 24N when they are 10m apart. Specific to the demonstration, please list and briefly describe three reasons why his claims must be wrong. One of your three points must be quantitative (must involve some type of force calculation).

Question 15

Suppose your instructor staggers into class the morning after an all-night 4x4 truck engine pulling party. She proceeds to do a demonstration in class where she measures a 100N force of attraction between two particles each carrying a positive charge of 1C and separated by 3m. Moreover she cuts the distance to ¼ of what it originally was and she claims the force then changes to a new value of 25N. Specific to the scientific content of her demonstration please give three reasons why you know that her claims are wrong; there's more than three, trust me. One of your three points must be quantitative - involving a force calculation of some sort.

Question 16

Suppose you are given two metal spheres on insulating stands, a plastic rod and some fur that you can rub the rod with to charge the rod. You cannot touch the spheres to ground using a wire, finger, etc. - you can just move them around using the insulated stands and touch them with the rod. They may touch each other if need be.
-Starting with both spheres neutral please describe how you would give the spheres equal net charges of the same sign.

Question 17

Suppose you are given two metal spheres on insulating stands, a plastic rod and some fur that you can rub the rod with to charge the rod. You cannot touch the spheres to ground using a wire, finger, etc. - you can just move them around using the insulated stands and touch them with the rod. They may touch each other if need be.
-Starting with neutral spheres please describe how you would give the spheres equal and opposite charges.

Question 18

Suppose you have two identical socks that repel each other with a certain force. Now you move them so they are three times as far apart as they were originally, but the force between them stays the same.
-What is one way in which the charges might change so the force could remain constant?

Question 19

Suppose you have two identical socks that repel each other with a certain force. Now you move them so they are three times as far apart as they were originally, but the force between them stays the same.
-In this case, let the charges remain the same as the socks separate so that the force decreases as they are separated. In moving the socks apart did the potential energy increase or decrease? Please explain.

Question 20

An atom under no external influences may be thought of as a positively charged nucleus surrounded by a negatively charged electron cloud. Now suppose the atom is placed in a uniform external electric field (like you'd find between two parallel charged plates). Please explain why this would stretch the atom out, elongating it.

Question 21

You and a friend are walking together along a beautiful shoreline. You get bored and begin to make electrostatics measurements. It turns out that you have a charge of +4 Coulombs and your friend a charge of -1 Coulombs. What is the product of your two charges?

A) +3 Coulombs
B) +3 square Coulombs
C) -20 square Coulombs
D) -20 Coulombs

Question 22

Electrons are

A) much lighter than protons
B) of the same mass as protons
C) much heavier than protons
D) of the same charge as protons.

Question 23

A charged object is able to repel

A) only charged objects
B) neutral objects and neutral particles
C) neutral objects but not neutral particles
D) only neutral particles

Question 24

After running a plastic comb through you hair several times you hold it above a small scrap of paper. The paper jumps off the table and sticks to the comb. But after some time the object flies off the comb. It leaves the comb because the paper becomes

A) magnetic.
B) electrically charged.
C) conducting.
D) electrically polarized.

Question 25

An atom under no external influences may be thought of as a positively charged nucleus surrounded by a negatively charged electron cloud. Now suppose the atom is placed in a uniform external electric field (like you'd find between two parallel charged plates). Please explain why this would result in no overall motion for the atom.

Question 26

Polarization

A) maximizes the potential energy of a system
B) minimizes the potential energy of a system
C) does not change the potential energy of a system
D) resets the potential energy of a system to zero.

Question 27

You have just built a house out in the country and it comes to your attention that you need to install a lightning rod. Being naturally curious you ask a hardware salesperson how lightning rods work and they correctly tell you that

A) they attract lightning.
B) they repel lightning.
C) they use corona discharge to bleed off local charge accumulations.
D) they use electrostatic precipitation to remove excess charge from the air.

Question 28

Who invented the xerographic copying process?

A) Wolfgang Pauli
B) Nicola Tesla
C) Chester Carlson
D) Thomas Edison

Question 29

In a conductor, the band gap between the valence band and the conduction band is

A) zero or very small.
B) small but non-zero.
C) moderately large, but not huge.
D) infinite.

Question 30

In a semiconductor, the band gap between the valence band and the conduction band is

A) zero or very small.
B) small but non-zero.
C) moderately large, but not huge.
D) infinite.

Question 31

In the dark, the photoconductors used in most xerographic copiers are

A) insulators.
B) semi-conductors.
C) conductors.
D) super-conductors.

Question 32

In further studying physics, you learn that light and particles have a dual nature, with light behaving like particle and vice versa. A particle (quantum) of light is called

A) a proton.
B) a neutron.
C) a photon.
D) an electron.

Question 33

A photoconductor cannot carry an electric current in the dark because all of its valence levels contain two electrons and moving a valence-level electron into one of the empty conduction levels requires too much energy. While the photoconductor would be able to carry current if its electrons could move from one valence level to another, such movement is impossible because

A) the velocity of an electron in the photoconductor is conserved and can't change.
B) no more than two electrons can be in each valence level: one spin-up and one spin-down.
C) the momentum of an electron in the photoconductor is conserved and cannot change.
D) the laws of motion prevent electrons from changing valence levels.

Question 34

A xerographic copier uses a special photoconductor surface that allows light from an original document to control the placement of black powder on white paper. The photoconductor only conducts electricity when it's exposed to light because, in the dark,

A) the photoconductor contains only negatively charged particles.
B) the photoconductor contains only positively charged particles.
C) electrons in the photoconductor completely fill its valence levels and can't shift from one level to another in order to transport charge through the material.
D) the photoconductor doesn't contain any electrically charged particles.

Question 35

You have covered a grounded metal surface with a layer of photoconductor. Working in the dark, you sprinkle negative charge onto this surface. If you now expose only the left half of the photoconductor to light, you will find that

A) the left half becomes neutral while the right half remains negatively charged.
B) nothing happens because there is no changing magnetic field.
C) negative charge flows from the right side of the photoconductor to the left and both sides become neutral.
D) the right half becomes neutral while the left half remains negatively charged.

Question 36

A photoconductor's electrical properties go from insulating to conducting when it is exposed to light because,

A) light allows extra electrons to move out of the valence band giving the semiconductor a positive charge.
B) light allows extra electrons to move into the conduction band giving the semiconductor a negative charge.
C) light supplies the energy needed to move electrons from the valence band to the conduction band.
D) light lowers the energy of the conduction levels eliminating the energy gap.

Question 37

The surface of a photoconductor has been coated with electric charge. This charge will remain in place until you expose the surface to

A) an electric field.
B) a magnetic field.
C) both an electric field and a magnetic field.
D) light.

Question 38

When a xerographic copier first applies electric charges to the surface of its photoconductor, it does so in the dark. The reason for applying these charges in the dark is that light exposure would

A) allow the charges to flow through the photoconductor so that they wouldn't accumulate on its surface.
B) release magnetic poles that would cancel the electric charges.
C) cause the magnetic poles to move, generating electricity that would neutralize the electric charges.
D) expand the coherence of the waves and prevent the charges from forming a real image on the surface.

Question 39

A typical commercial jet has a sharpened metal rod projecting backward from the tip of each wing. These two rods prevent the airplane from accumulating a large net electric charge during flight by

A) reducing sliding friction between the airplane and the passing air stream.
B) transferring any charge on the plane to the air behind the plane.
C) maintaining a steady electric current between the airplane's wings.
D) generating high voltages while passing quickly through the earth's magnetic field.

Question 40

Most commercial airliners have static dissipaters on their wingtips. These sharp metal spikes extend from the end of each metal wing and point toward the rear of the plane. Suppose a plane had just flown through a negatively charged cloud and acquired a large negative charge. It is now flying through neutral air. Which of the following should you expect to happen near the static dissipaters?

A) Any charge on the dissipaters will flow toward the wings, leaving the dissipaters neutral.
B) A corona discharge at the dissipater tips will spray negative charge into the air.
C) A corona discharge at the dissipater tips will spray positive charge into the air.
D) Nothing, because the air is neutral.

Question 41

In an insulator, the band gap between the valence band and the conduction band is

A) zero or very small.
B) small but non-zero.
C) moderately large, but not huge.
D) extremely large.

Question 42

Semiconductors

A) do not obey Ohm's law.
B) obey Ohm's law
C) do not use electrons to conduct electricity.
D) need light to work.

Question 43

You are an engineer and are building metal objects for a science lab that are supposed to hold charge for a long time. The object should not be

A) insulated from everything else.
B) smooth
C) sharp and pointed
D) circular

Question 44

Suppose you have a semiconductor and are not able to bias it such that any electrons leave the valence band. This object really then is a (an)

A) conductor
B) insulator
C) metal
D) lightning rod

Question 45

Suppose you have a semiconductor with many electrons that have been able to jump the band gap. This object really is a (an)

A) conductor
B) insulator
C) metal
D) lightning rod

Question 46

In a semi conductor the band gap is

A) an imaginary energy difference
B) a physical region where electrons do not exist.
C) a region of energies which the electrons cannot have.
D) the number of valence electrons minus the number of conducting ones.

Question 47

High voltage power lines are usually supported by glass insulators. An electric current cannot flow through a piece of glass because

A) glass contains only positively charged particles.
B) glass contains only negatively charged particles.
C) the electrons in the glass completely fill its valence levels and can't shift from one level to another to transport charge through the glass.
D) glass does not contain any electrically charged particles.

Question 48

Good electrical conductors are usually good thermal conductors because

A) neither type of object has a high specific heat.
B) both types of objects have low density.
C) of pure coincidence.
D) electrons are responsible for thermal and electric conduction.

Question 49

You decide to help your physics professor do an interactive classroom demonstration. You are standing on a plastic bench that insulates you from your surroundings. Both you and the helium balloon you are holding are electrically neutral. You now rub the balloon against your sweater, so that the balloon becomes negatively charged, and then let the balloon float away. You are left

A) with no negative electrically charged particles in your body.
B) with a negative electric charge.
C) electrically neutral.
D) with a positive electric charge.

Question 50

In a short circuit,

A) current flows normally.
B) no current flows.
C) electrons can take a short cut.
D) only small currents can flow.

Question 51

In an open circuit,

A) current flows normally.
B) no current flows.
C) electrons can take a short cut.
D) only open currents can flow.

Question 52

You notice that a light at home keeps going out but you are certain that the bulb is good. Such behavior could result from

A) either an open circuit or a short.
B) an open circuit only.
C) a short circuit only.
D) the bulb's resistance being cut in half.

Question 53

Your cat has chewed the cord to your desk lamp and has created a short circuit-an electric connection from one wire to the other inside the cord. When you plug the lamp into the electric outlet,

A) current will bypass the bulb and the bulb will not light up.
B) current will flow alternately through the bulb and through the short circuit, so that the bulb will blink on and off rapidly.
C) the current will begin to flow backward through the bulb so that it glows at half its normal brightness.
D) excessive current will pass through the bulb and the bulb will glow very brightly.

Question 54

Your pet tiger has chewed the cord to your desk lamp and has created an open circuit-an electronic rift between two points. When you plug the lamp into the electric outlet,

A) current will bypass the bulb and the bulb will not light up.
B) current will flow alternately through the bulb and through the open circuit, so that the bulb will blink on and off rapidly.
C) no current will flow at all and the bulb will not light up.
D) excessive current will pass through the bulb and the bulb will glow very brightly.

Question 55

A battery works because it

A) creates positive charge.
B) pumps positive charge from its positive terminal to its negative terminal.
C) creates negative charge.
D) pumps positive charge from its negative terminal to its positive terminal.

Question 56

The principal advantage of sending electric power across long distances using low current is that

A) the charge can get from one point to another faster.
B) electric power lost in the wires is greatly reduced.
C) the transmission lines are less likely to get in the way than low voltage transmission lines-which are much closer to the ground.
D) low current means low resistance in the lines.

Question 57

You are installing a new battery in your car. Although there are two terminals on the battery you hook up only one of your car's battery cables to the battery. Hooked up like this, the current that would then flow through the headlights when turned on is

A) zero.
B) twice the current that flowed when both terminals were present and plugged in.
C) the same as the current that flowed when both terminals were present and plugged in.
D) half the current that flowed when both terminals were present and plugged in.

Question 58

You remove the batteries from a working flashlight, turn both of them around as a pair, and reinsert them in the flashlight. They make good contact with the flashlight's terminals at both ends, so that there is no mechanical problem preventing the flashlight from working. If you now switch on the flashlight, it will

A) not work because only electrons can actually move through a circuit. The positively charged atomic nuclei are immobile.
B) work properly, although current will now be flowing backward through its circuit.
C) not work because the batteries can't send current backward through the flashlight's circuit.
D) not work because the light bulb can only carry electric current in one direction.

Question 59

For an appliance to receive and consume electric power,

A) a current must flow through it across a voltage decrease.
B) it must polarize the current with its magnetic field.
C) a current must flow through it across a voltage increase.
D) it must magnetize the current with its electric field.

Question 60

A resistor is essentially a poor conductor of electricity. When you send current through a resistor, that current always experiences a voltage drop, never a voltage rise. One way to understand this effect is that

A) more current leaves a resistor than enters it, so the voltage must go down to compensate.
B) it is easy to turn electric energy into thermal energy but not the other way around.
C) less current leaves a resistor than enters it, so the voltage must go down as well.
D) current can only flow forward through a resistor, never backward.

Question 61

Your flashlight has three identical 1.5 Volt batteries in it, arranged in a chain to give a total of 4.5 Volts. Current passes first through the first battery, then through the second battery, then through the third, on its way to the bulb. When you operate the flashlight, the batteries provide power to the flowing charges and they gradually use up their chemical potential energy. Which battery will run out of chemical potential energy first?

A) All three will run out at the same time.
B) The first battery will run out first.
C) The second battery will run out first.
D) The third battery will run out first.

Question 62

A rocking chair has damaged the cord of your desk lamp. One of the two wires in the cord is completely cut in half and cannot carry any current. However, the other wire still connects the lamp to the electric socket. If you turn on the lamp,

A) the normal amount of current will flow through both wires and the lamp will glow at its normal brightness.
B) the normal amount of current will flow through the one remaining wire and the lamp will glow at half its normal brightness.
C) no current will flow through either wire and the lamp will remain dark.
D) half the normal amount of current will flow through the one remaining wire and the lamp will glow at a quarter of its normal brightness.

Question 63

You have just put fresh batteries in your flashlight and it is working nicely. Now suppose that you remove both of the batteries and reinsert them backward. Despite the fact that the both batteries are reversed, they connect properly to one another and to the flashlight, so that there are no connection problems in the flashlight. As the result of this battery reversal, the flashlight will

A) work in reverse, lighting up when you put its switch in the "off" position and not lighting up when you put its switch in the "on" position.
B) remain lit regardless of the position of its on-off switch.
C) not light up at all, regardless of the position of its on-off switch.
D) work normally, lighting when you switch it "on" and turning off when you switch it "off."

Question 64

You have just put fresh batteries in your flashlight and it is working nicely. Now suppose that you remove one of the batteries and reinsert it backward. Despite the fact that the one battery is reversed, both batteries connect properly to one another and to the flashlight, so that there are no connection problems in the flashlight. As the result of this battery reversal, the flashlight will

A) work in reverse, lighting up when you put its switch in the "off" position and not lighting up when you put its switch in the "on" position.
B) remain lit regardless of the position of its on-off switch.
C) not light up at all, regardless of the position of its on-off switch.
D) work normally, lighting when you switch it "on" and turning off when you switch it "off."

Question 65

You drop your boom box and one of the two wires that connects the batteries to the electronics is severed. While you might hope that the device would continue working at half its normal volume, you find that it does not work at all. This is because both wires are necessary for the boom box to operate. One wire carries

A) current to the electronics and the other wire returns that current to the batteries.
B) electric current to the electronics while the other wire carries magnetic poles to the speakers.
C) electric fields to the electronics and the other wire carries magnetic fields to the electronics.
D) current to the amplifier while the other wire carries current to the speakers.

Question 66

A car stereo draws 24 A of current at voltage 12 V. What power does it use?

A) 288 W
B) 24 W
C) 12 W
D) 2 W

Question 67

A power line carries current 10 A and has resistance 2.0 $\Omega$ . What is the voltage drop across the line?

A) 200 V
B) 20 V
C) 10 V
D) 5 V

Question 68

Your new toaster has two separate toasting units, each of which consumes 600 watts of power when it is in use. When you operate one unit, a current of 5 amperes flows through the wiring in your home and the wires waste about 1 watt of power handling that current. If you operate both toasting units at once, your toaster consumes 1200 watts and the current flowing through the wiring in your home doubles to 10 amperes. How much power will the wires in your home waste now?

A) about 0.5 watts.
B) about 4 watts.
C) about 2 watts.
D) about 1 watt.

Question 69

A power line carries current 10 A and has resistance 2.0 $\Omega$ . What is the power loss as heat in the line?

A) 200 W
B) 20 W
C) 10 W
D) 5 W

Question 70

Two 1.5-V batteries placed end-to-end power a flashlight. If the current in the circuit is 0.6 A, what is the resistance in the bulb?

A) 5.0 $\Omega$
B) 2.5 $\Omega$
C) 1.8 $\Omega$
D) 0.9 $\Omega$

Question 71

A 60 watt, 120 volt light bulb is designed to operate at a 1/2 A current. If you screw this bulb into a fixture that is powered by very long thin wires it will glow more dimly than intended because the voltage drop across the bulb will be

A) less than 120 V and the current through the bulb will be less than 1/2 A.
B) 120 V, but the current through the bulb will be less than 1/2 A.
C) 120 V and the current through the bulb will be 1/2 A.
D) less than 120 V, but the current will still be 1/2 A.

Question 72

You are stranded on an Arctic wasteland with your physics class. Forget food and survival - you're playing with circuits to pass the long winter months. You have two batteries, some wire and two light bulbs. If you must use both batteries and both bulbs how would you hook them up so as to get
-maximum brightness

Question 73

You are stranded on an Arctic wasteland with your physics class. Forget food and survival - you're playing with circuits to pass the long winter months. You have two batteries, some wire and two light bulbs. If you must use both batteries and both bulbs how would you hook them up so as to get
-minimum (not zero!) brightness?

Question 74

You are stranded on an Arctic wasteland with your physics class. Forget food and survival - you're playing with circuits to pass the long winter months. You have two batteries, some wire and two light bulbs. If you must use both batteries and both bulbs how would you hook them up so as to get
-Suppose one battery delivers 3V and one bulb has a resistance of 0.2 Ω. Please calculate the power output of this one - bulb circuit and the current through the bulb.

Question 75

Suppose you have a 12V battery supplying current to a 6Ω resistor.

-Calculate the current through the resistor.

Question 76

Suppose you have a 12V battery supplying current to a 6Ω resistor.

-What is the value of the power being dissipated by the resistor?

Question 77

Suppose you have a 12V battery supplying current to a 6Ω resistor.

-If you trace electrons around the circuit, they actually go from high voltage to low voltage through the battery. Please explain why this takes energy from the battery.

Question 78

Suppose you have a 12V battery supplying current to a 6Ω resistor.

-As the current (moving charge) goes through the resistor what is happening to its potential energy?

Question 79

You are stranded on an island, passing time by making electric circuits using two batteries and two bulbs! This time, however your supplies are running dangerously low and you need to make the circuits where the batteries will last (retain their energy) the longest.
-Please explain how you would connect the circuits so as to achieve longest battery life.

Question 80

You are stranded on an island, passing time by making electric circuits using two batteries and two bulbs! This time, however your supplies are running dangerously low and you need to make the circuits where the batteries will last (retain their energy) the longest.
-The battery in any circuit actually moves electrons from high voltage to low voltage when it is supplying power. Please explain why this movement takes energy from the battery.