Physics

The secondary coil of a large transformer near the street supplies your home with 120 volt alternating current. The transformer's primary coil has 100 times as many turns as its secondary coil. At this moment, the transformer is supplying electric power only to your home and that power is 1200 watts. The transformer's primary coil is being supplied with (A) 12,000 volt alternating current and the current in that coil is 0.1 amperes. (B) 100 volt alternating current and the current in that coil is 1200 amperes (C) 120,000 volt alternating current and the current in that coil is 1/120 amperes. (D) 1200 volt alternating current and the current in that coil is 100 amperes.

(A) 12,000 volt alternating current and the current in that coil is 0.1 amperes.

The secondary coil of a large transformer near the street supplies your home with 120 volt alternating current. The transformer's primary coil has 50 times as many turns as its secondary coil. At this moment, the transformer is supplying electric power only to your home and that power is 6000 watts. The transformer's primary coil is being supplied with (A) 6,000 volt alternating current and the current in that coil is 1 ampere. (B) 6,000 volt alternating current and the current in that coil is 50 amperes (C) 120 volt alternating current and the current in that coil is 50 amperes. (D) 50 volt alternating current and the current in that coil is 120 amperes.

(A) 6,000 volt alternating current and the current in that coil is 1 ampere.

When they are far away from any external magnetic influences, two blocks of pure iron exert no magnetic forces on one another. Why not? (A) Each iron block contains many highly magnetic domains, but those domains are oriented in semi-random directions. The domains' magnetic fields cancel so each block appears non-magnetic. (B) Iron is a non-magnetic metal, meaning that it has no intrinsic magnetism, even at the atomic or molecular scale. (C) Each iron block is highly magnetic but its north pole is equally strong as its south pole. The attractive forces between opposite poles of the two blocks are therefore cancelled by the repulsive forces between like poles of the two blocks. (D) Each iron block contains as many north poles as it contains south poles. The net magnetic pole of each block is therefore zero and the blocks are completely non-magnetic.

(A) Each iron block contains many highly magnetic domains, but those domains are oriented in semi-random directions. The domains' magnetic fields cancel so each block appears non-magnetic.

A radio station emits a radio wave from an antenna that is located high in the air and far from any conducting surfaces. Why is the length of that transmitting antenna approximately 1/2 the radio wave's wavelength? (A) The antenna is then resonant at the radio station's frequency, making it easier for the station to move large amounts of charge up and down the antenna. (B) The antenna can then hold only a crest or a trough of the radio wave, ensuring that there is no destructive interference on the antenna. (C) The antenna needs to be long enough to accommodate the entire upward arrow of the radio wave's electric field. (D) The antenna needs to be long enough to accommodate the entire upward arrow of the radio wave's magnetic field.

(A) The antenna is then resonant at the radio station's frequency, making it easier for the station to move large amounts of charge up and down the antenna.

A motionless hydrogen atom has one electron and one proton. The electron has -1 fundamental unit of electric charge and the proton has +1 fundamental unit of electric charge. Which of the following statements correctly describes the energy of the electron in this atom? (A) The electron's energy is determined by its quantum standing wave. Since only certain quantum standing waves are possible in the atom, the electron can have only certain specific energies. (B) The electron's energy depends on the radius of its orbit around the nucleus. The electron can have any amount of energy, but that energy increases as its orbital radius decreases. (C) The electron's energy depends on its speed as it orbits around the nucleus. The electron can have any amount of energy, but that energy increases as the electron's orbital speed increases. (D) The electron's energy depends on the radius of its orbit around the nucleus. The electron can have any amount of energy, but that energy decreases as its orbital radius decreases.

(A) The electron's energy is determined by its quantum standing wave. Since only certain quantum standing waves are possible in the atom, the electron can have only certain specific energies.

When light that was traveling through empty space enters a gas, the light slows down slightly. What characteristic of the gas is responsible for slowing the light? (A) The gas contains electric charges. (B) The gas has energy. (C) The gas has mass. (D) The gas has pressure.

(A) The gas contains electric charges.

A local radio station employs the AM (amplitude modulation) technique to deliver a talk radio program to the radio receiver in your kitchen. How does this work? (A) The station varies the intensity of its radio wave to convey sound information to your receiver, which moves its speaker with each intensity change and thereby reproduces the sound. (B) The station uses sound from the talk show to vibrate its radio wave. When that vibrating wave reaches your receiver, it interacts with a tank circuit and shakes air back and forth in the speaker to produce sound. (C) The station uses sound from the talk show to vary the speed at which the radio wave travels. This sequence of fast and slow wave motion causes the air near the receiver's speaker to vibrate and become sound. (D) The station adds the sound waves to its radio wave and the pair travel together to your receiver. Your receiver than separates the sound waves from the radio wave and delivers the sound waves to its speaker.

(A) The station varies the intensity of its radio wave to convey sound information to your receiver, which moves its speaker with each intensity change and thereby reproduces the sound.

An FM radio station has an official frequency of 100 MHz (100 million cycles per second) and plays music you like. What aspect of the station's radio wave is conveying the information your receiver needs to reproduce the music? (A) The time interval between the radio wave's electric field peaks varies slightly to represent the music's air pressure variations. (B) The radio wave's electric field varies in direction, toward you and away from you, to represent fluctuations up and down in the music's air pressure. (C) The radio wave varies in height, moving up and down slightly, to represent fluctuations up and down in the music's air pressure. (D) The radio wave's energy varies slightly between electric energy and magnetic energy to represent the music's air pressure fluctuations.

(A) The time interval between the radio wave's electric field peaks varies slightly to represent the music's air pressure variations.

The power outlet in your room supplies 120 volt alternating current. That outlet has two metal slots through which power is provided. One slot is longer than the other. Which of the following statements is true about those two metal slots? (A) There are moments during which the voltage difference between those two slots is zero. (B) The voltage of the longer slot is always less than the voltage of the shorter slot. (C) The two slots have the same voltage, but that voltage increases and decreases alternately with the passage of time. (D) The voltage of the longer slot is always greater than the voltage of the shorter slot.

(A) There are moments during which the voltage difference between those two slots is zero.

The Fermi level in a particular solid material lies in the middle of a band of levels. In other words, the highest-energy electrons in that material partly fill a band of levels. This material is (A) an electrical conductor. (B) a photoconductor. (C) an electrical insulator. (D) a semiconductor.

(A) an electrical conductor.

A charged red balloon clings to a neutral window and a charged blue balloon clings to a neutral wall. If you bring those two balloons close together, they will (A) attract if they have opposite charges or repel if they have like charges. (B) repel. (C) neither attract nor repel. (D) attract.

(A) attract if they have opposite charges or repel if they have like charges.

On a bright day, the pupil of your eye (the circular opening through which you see) becomes very small in diameter. One consequence of having a tiny pupil is that (A) both distant and nearby objects appear relatively sharp at the same time. In other words, your depth of focus is large. (B) the sizes of the real images projected on your retina are relatively large compared to when your pupil is wide open. In other words, you see a slightly enlarged view of the world in front of you. (C) the sizes of the real images projected on your retina are relatively small compared to when your pupil is wide open. In other words, you see a slightly reduced view of the world in front of you. (D) distant and nearby objects do not appear relatively sharp at the same time. In other words, your depth of focus is small.

(A) both distant and nearby objects appear relatively sharp at the same time. In other words, your depth of focus is large.

The shiny surface of a CD or DVD is essentially a comb of microscopic mirrored strips that are separated by non-reflective gaps (something like this: ||||||||||||||||||||). When sunlight reflects from these rows of tiny mirrors, you see colors because the reflective strips (A) break each light wave up into pieces that can then interfere with one another. (B) refract the light waves so that certain colors travel faster to your eyes than other colors. (C) polarize the light waves so that only certain frequencies have horizontal polarizations and reflect. (D) short-circuit light waves that have the wrong wavelengths and absorb their energies.

(A) break each light wave up into pieces that can then interfere with one another.

A red LED and a red laser pointer both emit red light. A key difference between those two devices is that the LED emits (A) many small light waves and the laser pointer emits one large light wave. (B) lower frequency light than the laser pointer. (C) less light power than the laser pointer. (D) a wide light wave and the laser pointer emits a narrow light wave.

(A) many small light waves and the laser pointer emits one large light wave.

A permanent magnet sticks for years to your steel refrigerator because (A) the permanent magnet's magnetic field causes the steel's magnetic domains to rearrange so that they attract the permanent magnet. (B) electrons in the steel are attracted to the permanent magnet's south magnetic pole. (C) electrons in the steel are attracted to the permanent magnet's north magnetic pole. (D) electric currents flow through the steel and those electric currents are magnetic.

(A) the permanent magnet's magnetic field causes the steel's magnetic domains to rearrange so that they attract the permanent magnet.

You have three batteries: a 12.0-volt battery (from a car) and two 1.5-volt batteries (from a flashlight). Using clips and wires, you can link these batteries together in various chains. The possible voltage rises that you can obtain with these batteries are (A) 1.5 volts and 12.0 volts. (B) 1.5 volts, 3.0 volts, 9.0 volts, 10.5 volts, 12.0 volts, 13.5 volts, and 15.0 volts. (C) 1.5 volts, 3.0 volts, 10.5 volts, 12.0 volts, and 13.5 volts. (D) 1.5 volts, 3.0 volts, 12.0 volts, 13.5 volts, and 15.0 volts.

(B) 1.5 volts, 3.0 volts, 9.0 volts, 10.5 volts, 12.0 volts, 13.5 volts, and 15.0 volts.

During your international travels as a celebrity chef, you mistakenly plug your electric frying pan into a 240-volt electric outlet. It was designed to operate properly only on 120-volt electric power. When you turn it on, twice the normal current flows through the appliance and that current experiences twice the normal voltage drop as it passes through the appliance. The power being delivered to the electric frying pan is (A) 1/4 normal. (B) 4 times normal. (C) 2 times normal. (D) 1/2 normal.

(B) 4 times normal.

A particular AM radio station transmits a radio wave with a wavelength of 300 meters. It uses a simple monopole antenna, a vertical metal mast that rises upward above a horizontal conducting surface: the ground beneath the mast. For that mast to be resonant at the station's transmission frequency and as efficient as possible at emitting its radio wave, the mast is approximately (A) 3 meters in diameter. (B) 75 meters tall. (C) 300 meters tall. (D) 150 meters tall

(B) 75 meters tall.

You are recharging your cellphone and your power adapter contains a tiny transformer. Charges moving through the secondary coil of that transformer are picking up energy that is eventually used to recharge your phone. How is energy given to the charges in the coil? (A) Charges moving through the transformer's primary coil repel charges in its secondary coil and that repulsion does work on the charges in the secondary coil. (B) A changing magnetic field in the transformer produces an electric field. That electric field pushes the charges forward as they move forward through the secondary coil and thus does work on them. (C) Charges moving through the transformer's primary coil attract charges in its secondary coil and that attraction does work on the charges in the secondary coil. (D) A changing electric field in the transformer produces an magnetic field. That magnetic field pushes the charges forward as they move forward through the secondary coil and thus does work on them.

(B) A changing magnetic field in the transformer produces an electric field. That electric field pushes the charges forward as they move forward through the secondary coil and thus does work on them.

A twist-tie is a long, thin, sharp metal wire wrapped in paper. If you place a twist-tie in a microwave oven and turn the oven on, what will happen to the twist-tie? (A) The twist tie will remain cool, but electric charge will spray out of its sharp ends. (B) An electric current will flow through it, heating it up, and electric charge will also spray out of its sharp ends. (C) The twist tie will not be affected by the microwaves because it contains no water. (D) An electric current will flow through it, heating it up, but no charge will leave the wire.

(B) An electric current will flow through it, heating it up, and electric charge will also spray out of its sharp ends.

Which one of the following objects emits an electromagnetic wave that travels across the universe? (A) An electrically charged ball that is motionless at the top of a tall metal building. (B) An electrically charged ball on top of a flagpole that is waving back and forth in the wind. (C) An electrically charged ball that is traveling at constant velocity inside a glass elevator. (D) An electrically charged ball that is traveling at constant velocity on top of a metal truck.

(B) An electrically charged ball on top of a flagpole that is waving back and forth in the wind.

Suppose both coils of an ordinary transformer are carrying constant electric currents. Why can't the transformer transfer electric power from one coil to the other? (A) The two coils are electrically insulated from one another, so the transformer cannot transfer electric power between its coils, regardless of what types of currents those coils are carrying. (B) Each coil's constant current produces a constant magnetic field, which produces no electric field and therefore cannot do work or negative work on charges in the other coil's current. (C) Each coil's constant current produces no magnetic or electric field and therefore cannot do work or negative work on charges in the other coil's current. (D) Each coil's constant current produces a constant electric field, which produces no magnetic field and therefore cannot do work or negative work on charges in the other coil's current.

(B) Each coil's constant current produces a constant magnetic field, which produces no electric field and therefore cannot do work or negative work on charges in the other coil's current.

You use a converging lens to project the image of a flower on the wall of your dorm room. How does that lens form a sharp image of the flower on the wall? (A) The lens converges all of the light rays from the flower so that they all meet at a point half-way from the lens to the wall. Those rays continue on to form a sharp image on the wall. (B) The lens bends the light rays from a single point on the flower so that they converge to a single point on the wall. (C) The lens bends all the light rays from the entire flower so that they converge to a single point on the wall. (D) The lens bends the light rays from a single point on the flower so that they converge to a flower-shaped spot on the wall.

(B) The lens bends the light rays from a single point on the flower so that they converge to a single point on the wall.

What is the difference between a radio wave and a microwave? (A) The microwave has a smaller frequency than the radio wave. (B) The microwave has a shorter wavelength than the radio wave. (C) The microwave has a strong magnetic field than the radio wave. (D) The microwave has a weaker electric field than the radio wave.

(B) The microwave has a shorter wavelength than the radio wave.

When you plug your hairdryer into a household electric outlet, the two metal blades of its plug connect with the two slots in the outlet. You turn the hairdryer on and the outlet supplies 120-volt alternating current to the hairdryer. What is happening at those two connections? (A) The voltage difference between the two connections reverses many times per second, but the current flowing through each connection remains constant. (B) The voltage difference between the two connections reverses many times per second and the current flowing through each connection also reverses many times per second. (C) The current flowing through each connection reverses many times per second, but the voltage difference between the two connections remains constant. (D) At one moment, current flows through the left connection to the hairdryer and zero current flows through the right connection. A fraction of a second later, current flows through the right connection to the hairdryer and zero current flows through the left connection. This arrangement of current flow to the hairdryer alternates back and forth many times per second.

(B) The voltage difference between the two connections reverses many times per second and the current flowing through each connection also reverses many times per second.

Why does the United States' electric power grid use alternating current rather than direct current? (A) Alternating current is less dangerous than direct current. (B) Transferring power from circuit to circuit using transformers can only work if the current changes with time. (C) Direct current produces no magnetic field. Alternating current does produce a magnetic field and thereby doubles the amount of power that a wire can deliver. (D) Direct current has lower voltages than alternating current and therefore less power.

(B) Transferring power from circuit to circuit using transformers can only work if the current changes with time.

A microwave oven heats food primarily through its water content. What aspect of water makes it especially susceptible to heating by microwaves? (A) Water molecules are charged (have a net electric charge), so microwaves exert fluctuating forces on them. (B) Water molecules are polar (have an electric polarization), so microwaves exert fluctuating torques on them. (C) Water molecules are charged (have a net electric charge), so microwaves exert fluctuating torques on them. (D) Water molecules are polar (have an electric polarization), so microwaves exert fluctuating forces on them.

(B) Water molecules are polar (have an electric polarization), so microwaves exert fluctuating torques on them.

Your pet rabbit chews through the extension cord supplying power to your computer and produces a short circuit: the two metal wires in the cord become electrically connected to one another. If no safety mechanisms existed, what would happen to the extension cord and your computer? (A) Both your computer and the cord would become hot. (B) Your computer would receive approximately zero power and the cord would become hot. (C) Your computer would operate properly, but the cord would become hot. (D) The cord would remain cool, but your computer would become hot.

(B) Your computer would receive approximately zero power and the cord would become hot.

An LED (light emitting diode) produces a photon (a single quantum wave of light) when an electron (A) stimulates the emission of another electron from the diode's valence levels. (B) crosses the diode's junction and then makes a radiative transition from a conduction level to an empty valence level. (C) makes a radiative transition from the diode's n-type semiconductor to its p-type semiconductor. (D) collides with an atom in the diode's gas discharge and causes that atom to emit an electromagnetic wave.

(B) crosses the diode's junction and then makes a radiative transition from a conduction level to an empty valence level.

Electric power is transmitted long distances as a relatively small current at a relatively high voltage because the power wasted in the transmission wires is (A) proportional to the current, so reducing that current reduces the wasted power. (B) proportional to the square of the current, so reducing that current dramatically reduces the wasted power. (C) inversely proportional to the square of the voltage (i.e., proportional to 1/voltage^2), so increasing that voltage dramatically reduces the wasted power. (D) inversely proportional to the voltage (i.e., proportional to 1/voltage), so increasing that voltage reduces the wasted power.

(B) proportional to the square of the current, so reducing that current dramatically reduces the wasted power.

Liquid water heats faster in the microwave oven than solid ice because only the molecules in liquid water can (A) translate (move) in response to the forces exerted on them by the microwave's electric field. (B) rotate in response to the torques exerted on them by the microwave's electric field. (C) translate (move) in response to the forces exerted on them by the microwave's magnetic field. (D) rotate in response to the torques exerted on them by the microwave's magnetic field.

(B) rotate in response to the torques exerted on them by the microwave's electric field.

The electric power grid in the United States uses alternating current because (A) alternating current is less likely to cause an electrical fire than direct current. (B) transformers can move power from one circuit to another only if those circuits are carrying alternating currents. (C) an alternating current carries more electric power than a direct current. (D) an alternating current delivers both positive and negative charges, while a direct current delivers only positive charges. That difference makes alternating current twice as efficient as direct current.

(B) transformers can move power from one circuit to another only if those circuits are carrying alternating currents.

When a long piece of wire is carrying a 5-ampere current, the wire exhibits a voltage drop of 1 volt. When that wire is carrying a 10-ampere current, the wire's voltage drop is (A) 0.5 volts. (B) 1 volt. (C) 2 volts. (D) 4 volts.

(C) 2 volts.

During your semester abroad, you purchase a hair appliance designed to operate on 240-volt electric power. Its heating element is an electrical resistor, with a behavior that is accurately described by Ohm's law. When supplied with 240-volt electric power, a current of 5 amperes flows through the heating element and it consumes 1200 watts of electric power. When you supply it with 120-volt electric power upon your return to the United States, what happens? (A) A current of 5 amperes flows through it and it consumes 600 watts of electric power. (B) A current of 5 amperes flows through it and it consumes 2400 watts of electric power. (C) A current of 2.5 amperes flows through it and it consumes 300 watts of electric power. (D) A current of 10 amperes flows through it and it consumes 4800 watts of electric power.

(C) A current of 2.5 amperes flows through it and it consumes 300 watts of electric power.

Which one of the following objects emits an electromagnetic wave that travels across the universe? (A) An electrically charged ball that is motionless at the top of a tall metal building. (B) An electrically charged ball that is traveling at constant velocity on top of a metal truck. (C) An electrically charged ball that is going around in a circle at a constant speed on a plastic merry-go-round. (D) An electrically charged ball that is traveling at constant velocity inside a glass elevator.

(C) An electrically charged ball that is going around in a circle at a constant speed on a plastic merry-go-round.

When 120 volt AC power is connected to the primary coil of a particular transformer, the secondary coil of that transformer supplies 30 volt AC power to its secondary circuit. Suppose you modify the transformer's secondary coil, doubling the number of turns in that secondary coil. How does that change affect the coil and secondary circuit? (A) Each charge moving through the secondary coil now has twice as much work done on it by the transformer's magnetic field. The coil now supplies 60 volt AC power to its secondary circuit. (B) Twice as much current now flows through the secondary coil. The coil now supplies 15 volt AC power to its secondary circuit. (C) Each charge moving through the secondary coil now has twice as much work done on it by the transformer's electric field. The coil now supplies 60 volt AC power to its secondary circuit. (D) Twice as much current now flows through the secondary coil. The coil still supplies 30 volt AC power to its secondary circuit.

(C) Each charge moving through the secondary coil now has twice as much work done on it by the transformer's electric field. The coil now supplies 60 volt AC power to its secondary circuit.

An electromagnet is a coil of wire that becomes magnetic due to electricity. What aspect of electricity makes it magnetic? (A) Electric charge is magnetic. (B) Electric polarization is magnetic. (C) Electric current is magnetic. (D) Electric voltage is magnetic.

(C) Electric current is magnetic.

If you put a thick metal spoon in a microwave oven, what will happen? (A) The spoon will have no effect on the microwaves in the oven. (B) The spoon will become radioactive. (C) Microwaves in the oven will cause electric currents to flow in the metal spoon. (D) No microwaves will be able to form in the oven.

(C) Microwaves in the oven will cause electric currents to flow in the metal spoon.

Your electric hairdryer was designed to operate on 120 volt alternating current. You are traveling in South Asia and your friend connects it to the local electric power, which is 240 volt alternating current. What happens to your electric hairdryer? (A) The hairdryer's heating element consumes the correct amount of electric power and operates normally. (B) The correct amount of current flows through the electric hairdryer's heating element, but that current alternates too rapidly and overheats the heating element. (C) The current in the hairdryer's heating element is about twice as large as it should be. The heating element consumes about 4 times as much power as it should and overheats. (D) The temperature of 240 volt alternating current is much higher than the hairdryer was designed to handle and it overheats.

(C) The current in the hairdryer's heating element is about twice as large as it should be. The heating element consumes about 4 times as much power as it should and overheats.

If you carry a portion of positive charge from a region of high voltage to a region of low voltage, that charge will (A) do negative work on you during that move. (B) become a smaller positive charge as a result of that move. (C) do work on you during that move. (D) become negative charge as a result of that move.

(C) do work on you during that move.

A strong bar magnet has one north pole and one south pole. Dropping the magnet onto the floor breaks it in half, so that one piece is the former north pole and the other piece is the former south pole. You examine those two pieces and find that (A) the former north pole has a net south pole and the former south pole has a net north pole. (B) the former north pole has a net north pole and the former south pole has a net south pole. (C) each piece has zero net pole. (D) both pieces have net south pole.

(C) each piece has zero net pole.

Radio and microwave devices use tank circuits to help them move enough electric charge to produce strong electromagnetic waves. At its most basic level, a tank circuit consists of a capacitor (two surfaces that can store separated electric charge) and an inductor (an electromagnet that can carry current). When a tank circuit is helping a device produce an electromagnetic wave, (A) the tank circuit carries current only in one direction so that the current flows up the antenna and becomes an electromagnetic wave. (B) the tank circuit is accelerating up and down rhythmically, in sync with the electromagnetic wave. (C) energy in the tank circuit is shifting back and forth rhythmically between the capacitor's electric field and the inductor's magnetic field. (D) the tank circuit is turning AC electric power into DC electric power and thereby strengthening the electromagnetic wave.

(C) energy in the tank circuit is shifting back and forth rhythmically between the capacitor's electric field and the inductor's magnetic field.

When you connect an electromagnet to a source of alternating current, its magnetization reverses direction repeatedly. An electric charge near that AC electromagnet (A) experiences a force directly from the AC electromagnet's magnetic field. (B) experiences zero force because the AC electromagnet's magnetic field averages to zero. (C) experiences a force because the AC electromagnet's changing magnetic field produces an electric field. (D) experiences zero force because it is not affected by magnetic fields.

(C) experiences a force because the AC electromagnet's changing magnetic field produces an electric field.

Your toaster is consuming 1000 watts of electric power. That power traveled to Charlottesville in high-voltage transmission wires carrying a total of 100 million watts (100,000,000 watts). What fraction of the electric charges passing through those transmission wires also pass through your toaster? (A) 1 part in 10,000. (B) 1 part in 1,000,000 (C) zero. (D) 1 part in 100,000.

(C) zero.

You have two identical electric space heaters, both of which are plugged into the same electrical outlet of your home. It's a cold winter day and you turn on one of the heaters. A current of 10 amperes flows through the wires of your home (to provide power to the heater) and wastes 1 watt in those wires. When you turn on the second heater, a current of (A) 20 amperes flows through the wires of your home and wastes 2 watts in those wires. (B) 10 amperes flows through the wires of your home and wastes 2 watts in those wires. (C) 40 amperes flows through the wires of your home and wastes 2 watts in those wires. (D) 20 amperes flows through the wires of your home and wastes 4 watts in those wires.

(D) 20 amperes flows through the wires of your home and wastes 4 watts in those wires.

The transformer in your home theater system has 120 turns in its primary coil and 40 turns in its secondary coil. With 120-volt AC power connected to the primary coil and a current of 5 amperes flowing through that primary coil, the transformer's secondary coil is supplying (A) 8-volt AC power and a current of 24 amperes is flowing through that secondary coil. (B) 5-volt AC power and a current of 40 amperes is flowing through that secondary coil. (C) 24-volt AC power and a current of 8 ampere is flowing through that secondary coil. (D) 40-volt AC power and a current of 15 amperes is flowing through that secondary coil.

(D) 40-volt AC power and a current of 15 amperes is flowing through that secondary coil.

A sharp metal pin has a voltage of +1000 volts and it points toward a wide metal surface with a voltage of -1000 volts (see figure). What is the voltage midway between the surface and the pin? (A) 0 volts. (B) A positive voltage less than +1000 volts. (C) A positive voltage greater than +1000 volts. (D) A negative voltage.

(D) A negative voltage.

A capacitor consists of two conducting surfaces separated by an insulator. When those two conducting surfaces have equal but opposite electric charges, what is present in the separating insulator? (A) A magnetic field pointing toward the negatively charged surface. (B) An electric field pointing toward the positively charged surface. (C) A magnetic field pointing toward the positively charged surface. (D) An electric field pointing toward the negatively charged surface

(D) An electric field pointing toward the negatively charged surface

When you place a ceramic mug of coffee in a microwave oven and turn that oven on, the coffee's temperature increases. What is it about coffee that causes it to heat in the microwave oven? (A) Coffee contains water molecules and each water molecule has a large magnetic dipole (a north end and a south end). (B) Coffee has a positive electric charge and the microwaves magnetize that electric charge. (C) The microwave oven blows hot air across the mug of coffee and allows heat to flow into the coffee. (D) Coffee contains water molecules and each water molecule has a large electric dipole (a positive end and a negative end).

(D) Coffee contains water molecules and each water molecule has a large electric dipole (a positive end and a negative end).

A transformer's primary coil receives power from the electric company and it provides power from its secondary coil. To increase the voltage of power provided from the secondary coil, what must you do? (A) Increase the amount of iron used in the core and frame of the transformer. (B) Decrease the amount of iron used in the core and frame of the transformer. (C) Decrease the number of turns in the secondary coil. (D) Increase the number of turns in the secondary coil.

(D) Increase the number of turns in the secondary coil.

Two identical magnetic stickers, offering pizza delivery information, are clinging to your refrigerator. If you bring those two stickers near one another they will (A) repel. (B) attract. (C) neither attract nor repel. (D) attract, repel, or neither, depending on how their magnetic poles are positioned relative to one another

(D) attract, repel, or neither, depending on how their magnetic poles are positioned relative to one another

A battery charger recharges a battery by (A) pushing current through the battery from its negative terminal to its positive terminal. (B) connecting a wire between the battery's positive terminal and its negative terminal. (C) removing positive charges from the battery's positive terminal and negative charges from its negative terminal. (D) pushing current through the battery from its positive terminal to its negative terminal.

(D) pushing current through the battery from its positive terminal to its negative terminal.

You are heating water in a hotpot that is plugged into an electric outlet. Like most electric conductors, the heating element in the hotpot obeys Ohm's law. At this moment, the current flowing through that heating element is proportional to (A) one divided by the voltage difference between the two ends of the heating element. (B) the net charge on the heating element. (C) one divided by the net charge on the heating element. (D) the voltage difference between the two ends of the heating element.

(D) the voltage difference between the two ends of the heating element.

The electrons in a large atom aren't all in the lowest energy orbital (the orbital closest to the atom's nucleus). That's because (A) centrifugal force swings the electrons outward, away from the atom's nucleus. (B) the electrons are repelled by the nucleus and move away from it. (C) forces prevent electrons from approaching the atom's nucleus, so they distribute themselves uniformly among the atom's outer orbitals. (D) two identical electrons can never be in the same quantum wave.

(D) two identical electrons can never be in the same quantum wave.

When an electric power is transmitted long distances, it is usually carried through the wires by a small current at a large voltage. Power is transmitted that way because? A) A smaller current wastes less power in the wires B) It does not require the use of a complete circuit C) It does not require the use of transformers D) A larger voltage wastes less power in the wires

A) A smaller current wastes less power in the wires

The electric motor in a toy car has a permanent magnet rotor and stationary electromagnets. When the motor is propelling the car, the poles of its electromagnets? A) Attract the rotors' poles as they approach and repel the rotors poles as they separate B) Repel the rotors poles as they approach and repel the rotors poles as they separate C) Attract the rotors poles as they approach and attract the rotors poles as they separate D) Repel the rotors poles as they approach and attract the rotors poles as they separate

A) Attract the rotors' poles as they approach and repel the rotors poles as they separate

When the MOSFET device that we discussed in class and in the book has zero charge on its gate surface, its middle portion (the 'channel') cannot conduct current. Putting positive charge on the gates surface can allow the MOSFET to conduct current by? A) Attracting electron into the channel, where they fill some of the conduction levels B) Attracting electrons into the channel so that the valence levels are then completely filled and the conduction levels are completely empty C) Bending the channel toward the gate surface and removing the kink that had been pinching off the flow of the electric current D) Pushing positive charge out of the channel, where that positive charge had been blocking the flow of the electric current

A) Attracting electron into the channel, where they fill some of the conduction levels

The power adaptor for your clock radio contains a transformer, several diodes, and a capacitor. The purpose of the diodes is to convert? A) High-voltage alternating current into low-voltage alternating current B) Low-voltage direct current into low-voltage alternating current C) Low-voltage alternating current into low-voltage direct current D) High-voltage direct current into low-voltage direct current

A) High-voltage alternating current into low-voltage alternating current

When an alternating current flows through the primary coil of a transformer, the magnetization of the transformer's iron core reverses rapidly. The changing magnetization can provide power to current in the transformer's secondary coil by? A) Producing an electric field that can do work on charge flowing through the secondary coil B) Magnetically polarizing the current in the secondary coil C) Shaking charges in the secondary coil and sending them out of the coil with extra energy D) Heating charges in the secondary coil and sending them out of the coil with extra energy

A) Producing an electric field that can do work on charge flowing through the secondary coil

The sky is blue rather than pink at midday because? A) Tiny particles in the air are more efficient at Rayleigh scattering violet light waves than they are at scattering red light waves B) Tiny particles in the air absorb red light more efficiently than they absorb violet light C) Air molecules are slightly blue in color and they impart that color to the sunlight passing through them D) Sunlight that reflects from the bleu oceans, seas, and lakes colors the sky blue

A) Tiny particles in the air are more efficient at Rayleigh scattering violet light waves than they are at scattering red light waves

A microwave heats food primarily through the food's water. Liquid water heats up when exposed to intense microwave because the fluctuating? A) electric field in the microwave twists water molecules back and forth rapidly B) electric field in the microwave propels strong electric current through the water C) Magnetic field in the microwave induces strong electric currents in the water D) Magnetic field in the microwave magnetizes the water molecules and shakes them vigorously back and forth

A) electric field in the microwave twists water molecules back and forth rapidly

The difference between a metal and an insulator lies in their band structures. An insulator is unable to connect electric current in response to an electric field because? A) Its band structure prevents it electrons from crossing the mid-point of the material without becoming positively charged B) All of its electrons reside in filled bands and thus can't shift into empty levels so as to move across the materials C) Its band structure prevents it from becoming electrically charged, as it must do in order to conduct current D) Its band structure puts the guitars on the left and the drums on the right, so there is no room for the lead vocal

B) All of its electrons reside in filled bands and thus can't shift into empty levels so as to move across the materials

The difference between metal and an insulator lies in their band structures. A metal is able to conduct electric current in response to an electric field because? A) All of its electrons reside in filled bands and are therefore free to move across the material in response to electric fields B) Its band structure does not require it to become electrically charged, so it can conduct current in response to electric fields C) Its band structure allows it electrons to cross the midpoint of the material without becoming positively charged D) Its electrons only partially fill the highest energy band they occupy so those electrons can move in response to electric fields

B) Its band structure does not require it to become electrically charged, so it can conduct current in response to electric fields

A microwave oven reheats your coffee by exposing that coffee to an intense microwave, an electromagnetic wave with a wavelength of about 12cm. The coffee becomes hotter because? A) A microwave is much hotter than the coffee and heat flows naturally from the hotter microwave to the cold coffee B) The microwave's alternating electric field exerts torque on the polar water molecules in the coffee and those molecules rotate and rub against one another C) The microwaves alternating electric field exerts forces on the charged water molecules in the coffee and those molecules move and collide with one another D) The microwave undergoes Rayleigh scattering as it encounters the coffee and it vibrates the coffee molecules so that they become hotter

B) The microwave's alternating electric field exerts torque on the polar water molecules in the coffee and those molecules rotate and rub against one another

The transformer in a power adaptor has 120 turns in its primary coil and 10 turns in its secondary coil. With 120 volt AC power connected to the primary coil and a current of 1 ampere flowing through that primary coil, the transformer's secondary coil is supplying? A) 12 volt AC power and a current of 10 ampere is flowing through that secondary coil B) 10 volt AC power and a current of 10 amperes is flowing through that secondary coil C) 10 volt AC power and a current of 12 ampere's is flowing through that secondary coil D) 12 volt AC power and a current of 12 amperes is flwoing through that secondary coil

C) 10 volt AC power and a current of 12 ampere's is flowing through that secondary coil

The transformer in a power adaptor has 120 turns in its primary coil and 12 turns in its secondary coil. With 120 volt AC power connected to the primary coil and a current of 1 ampere flowing through that primary coil, the transformer's secondary coil is supplying? A) 10 volt AC power and a current of 12 ampere's is flowing through that secondary coil B) 10 volt AC power and a current of 10 amperes is flowing through that secondary coil C) 12 volt AC power and a current of 10 ampere is flowing through that secondary coil D) 12 volt AC power and a current of 12 amperes is flowing through that secondary coil

C) 12 volt AC power and a current of 10 ampere is flowing through that secondary coil

As it travels through otherwise empty space, a radio wave consists of? A) An electric charge, a magnetic pole, an electric field, and a magnetic field B) An electric charge and a magnetic pole C) An electric field and a magnetic field D) An electric field and an electric charge

C) An electric field and a magnetic field

If the speed of light in water did not depend on the wavelength of that light a rainbow would? A) Appear reversed in color, with red on the inside and violet on the outside B) Not appear at all C) Appear white D) Still appear red on the outside and violet on the inside

C) Appear white

Compared to a pure semiconductor, a n-type semiconductor has some extra electrons and a p-type semiconductor has some missing electrons. Suppose you have two electrically neutral disks, one of n-type semiconductor and one of p-type semiconductor. When you touch the two disks? A) No movement of electrons occurs because semiconductors contain no mobile electric charge and cannot conduct electric charge B) NO movement of electron occurs because such movement would spoil the electrical neutrality of the two disks C) Electrons migrate from the n-type semiconductors to the p-type semiconductor and form a depletion region (a region that resembles pure semiconductor) D) Electrons migrate from the p-type semiconductor to the n-type semiconductor and from a depletion region (a region that resembles pure semiconductor)

C) Electrons migrate from the n-type semiconductors to the p-type semiconductor and form a depletion region (a region that resembles pure semiconductor)

You accidentally leave a thick spoon in a glass bowl of soup that you put in the middle of the microwave oven. When you turn on the microwave oven? A) Sparks shoot out of the spoon toward the top of the ovens cooking chamber B) The spoon becomes radioactive so that it should be discarded where no one else will come into contact with it C) Nothing unusual happens because the spoon is a good electrical conductor and has smooth ends D) The spoon becomes extremely hot and scorches the soup in only a few seconds

C) Nothing unusual happens because the spoon is a good electrical conductor and has smooth ends

Your hair dryer was designed to operate on 120 volt alternating current, but you are travelling in Europe and your friend connects It to a 230 volt alternating current. The hairdryer quickly burns out because? A) While the correct amount of current flows through the hairdryer's heating element, that current alternates too rapidly and overheats the heating element B) The temperature of 230 volt alternating current is much higher than the hairdryer was designed to handle and it burns up the hairdryer C) The electric field in the hairdryer's heating element is too strong and that field pushes too much current through the heating element D) While the correct amount of current flows through the hairdryers heating element, that current produces too many volts in the heating element and burns it up

C) The electric field in the hairdryer's heating element is too strong and that field pushes too much current through the heating element

Your hair dryer was designed to operate on 120 volt alternating current, but you are travelling in Europe and your friend connects It to a 230 volt alternating current. The hairdryer quickly burns out because? A) The correct amount of current flows through the hair dryers heating element, but that current produces too many volts in the heating element and burns it up B) The correct amount of current flows through the hair dryers heating element, but that current alternates too rapidly and overheats the heating element. C) The voltage gradient in the hair dryers heating element is too large and too much current flows through the heating element D) The temperature of 230 volt alternating current is much higher than the hair dryer was designed to handle and it burns up the hairdryer

C) The voltage gradient in the hair dryers heating element is too large and too much current flows through the heating element

You re listening to an AM radio station as your drive across the plains of Kansas. It is so flat that you can see the stations vertical transmitting antenna, even though that antenna is 10 miles north of you. As that stations radio wave passes by you, its electric field points? A) Vertically up and down and it magnetic field points horizontally north and south B) Horizontally north and south and its magnetic field points horizontally east and west C) Vertically up and down and its magnetic field points horizontally east and west D) Horizontally eat and west and its magnetic field points horizontally north and south

C) Vertically up and down and its magnetic field points horizontally east and west

You have a typical motor/generator, consisting of a rotating permanent magnet and a stationary coil of wire. There is a crank attached to the rotating magnet and you are exerting a torque on that crank. The device acts as? A) A generator when you twist it in the direction of its rotation and it acts as a motor when you twist it opposite the direction of its rotation B) A motor when you twist it in the direction of its rotation and it acts as a generator when you twist it opposite the direction of its rotation C) A generator D) A motor

D) A motor

The electric power grid in the United States uses alternating current because? A) Alternating current is less likely to cause an electrical fire than direct current B) Transformers can move power from one circuit to another only if those circuits are carrying alternating currents C) An alternating current delivers both positive charge and negative charges, while a direct current delivers only positive charges. That difference makes alternating current twices as efficient as direct current D) An alternating current carries more electric power than a direct current

D) An alternating current carries more electric power than a direct current

When a light wave is midway between a distant star and your eye, that wave consists of? A) A magnetic field and either an electric field or electric charge B) An electric field and either a magnetic field or magnetic pole C) Either an electric field or an electric charge, and either a magnetic field or a magnetic pole D) An electric field and a magnetic field, but no electric charges or magnetic poles

D) An electric field and a magnetic field, but no electric charges or magnetic poles

You have two bar magnets that are identical except that one has twice the mass of the other. The net magnetic pole of the larger magnet is? A) Four times the net magnetic pole of the smaller magnet B) Twice the net magnetic pole of the smaller magnet C) Half the net magnetic pole of the smaller magnet D) Equal to the net magnetic pole of the smaller magnet

D) Equal to the net magnetic pole of the smaller magnet

You are boating on a vast lake and listening to an AM radio station. You can see the stations vertical transmitting antenna on the shore, directly to your west. As that radio wave passes by you, its electric field points? A) Horizontally north and south and its magnetic field points horizontally east and west B) Vertically up and down and its magnetic field points horizontally east and west C) Horizontally east and west and its magnetic field points horizontally north and south D) Vertically up and down and its magnetic field points horizontally north and south

D) Vertically up and down and its magnetic field points horizontally north and south

Equation for turns and voltage?

Turns Primary x Current Primary = Turns Secondary x Current Secondary and Voltage Primary x Current Primary = Voltage Secondary x Current Secondary