Physics 1060 - Spring 2014 - Midterm 2 - Posted Version with Solutions
Problem 1:
A battery charger recharges a battery by
(A) making current flow through the battery from its negative terminal to its positive terminal. [14.4% picked]
(B) removing positive charges from the battery's positive terminal and negative charges from its negative terminal. [1.1% picked]
(C) connecting a wire between the battery's positive terminal and its negative terminal. [0.4% picked]
(D) making current flow through the battery from its positive terminal to its negative terminal. [84.2% picked]
Answer: (D) making current flow through the battery from its positive terminal to its negative terminal. [84.2% picked]
Problem 2:
You are about to push two coins off a horizontal table simultaneously, a US quarter (big coin) and US dime (little coin). They start side-by-side near the edge of the table and you push them equally hard for equal times. Off they go! Which of the following choices correctly describes what happens to the coins?
(A) The quarter hits the floor first, although both coins hit the floor at the same distance from the table. [1.4% picked]
(B) They hit the floor at the same time and at the same distance from the table. [44.0% picked]
(C) They hit the floor at the same time, but the dime hits the ground farther from the table than does the quarter. [53.5% picked]
(D) The dime hits the floor first, although both coins hit the floor at the same distance from the table. [1.1% picked]
Answer: (C) They hit the floor at the same time, but the dime hits the ground farther from the table than does the quarter. [53.5% picked]
Problem 3:
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. [2.5% picked]
(B) An electric current will flow through it, heating it up, and electric charge will also spray out of its sharp ends. [96.1% picked]
(C) The twist tie will not be affected by the microwaves because it contains no water. [0.0% picked]
(D) An electric current will flow through it, heating it up, but no charge will leave the wire. [1.4% picked]
Answer: (B) An electric current will flow through it, heating it up, and electric charge will also spray out of its sharp ends. [96.1% picked]
Problem 4:
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. [41.7% picked]
(B) The voltage of the longer slot is always less than the voltage of the shorter slot. [5.3% picked]
(C) The two slots have the same voltage, but that voltage increases and decreases alternately with the passage of time. [44.2% picked]
(D) The voltage of the longer slot is always greater than the voltage of the shorter slot. [8.8% picked]
Answer: (A) There are moments during which the voltage difference between those two slots is zero. [41.7% picked]
Problem 5:
Why is it energy-inefficient to transmit power long distances as large currents in two wires having a small difference in voltage?
(A) The power a pair of wires wastes as thermal power is proportional to one divided by the square of the voltage difference between those wires. [9.2% picked]
(B) The power a wire wastes as thermal power is proportional to the current it carries. [12.3% picked]
(C) The power a pair of wires wastes as thermal power is proportional to one divided by the voltage difference between those wires. [2.5% picked]
(D) The power a wire wastes as thermal power is proportional to the square of the current it carries. [76.1% picked]
Answer: (D) The power a wire wastes as thermal power is proportional to the square of the current it carries. [76.1% picked]
Problem 6:
A long bar magnet (a permanent magnet) has a north pole at its red-painted end and a south pole at its white-painted end. You break that magnet exactly in half, so that you have a red-painted half and a white-painted half. Which of the following correctly describes the two halves?
(A) Each half has both a north pole and a south pole, and the net pole of each half is exactly zero. [92.6% picked]
(B) Each half has both a north pole and a south pole, however, the red-painted half has a stronger north pole than south pole and the white-painted half has a stronger south pole than north pole. [3.5% picked]
(C) The two halves have no magnetic poles at all. [2.8% picked]
(D) The red-painted half has only a north pole and the white-painted half has only a south pole. [1.1% picked]
Answer: (A) Each half has both a north pole and a south pole, and the net pole of each half is exactly zero. [92.6% picked]
Problem 7:
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. [2.1% picked]
(B) 75 meters tall. [75.0% picked]
(C) 300 meters tall. [8.1% picked]
(D) 150 meters tall. [14.8% picked]
Answer: (B) 75 meters tall. [75.0% picked]
Problem 8:
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. [51.6% picked]
(B) The gas has energy. [2.1% picked]
(C) The gas has mass. [32.5% picked]
(D) The gas has pressure. [13.8% picked]
Answer: (A) The gas contains electric charges. [51.6% picked]
Problem 9:
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. [1.8% picked]
(B) Decrease the amount of iron used in the core and frame of the transformer. [0.4% picked]
(C) Decrease the number of turns in the secondary coil. [10.6% picked]
(D) Increase the number of turns in the secondary coil. [87.3% picked]
Answer: (D) Increase the number of turns in the secondary coil. [87.3% picked]
Problem 10:
Someone has hidden a radio transmitter and antenna somewhere on the UVa grounds. You measure the transmitter's radio wave at several locations around grounds and find that, while the wave's electric field is always vertical, the wave's horizontal magnetic field points in different horizontal directions at different locations around grounds. Using a paper map, how might you find the transmitter and antenna?
(A) At each measurement location, draw a line that is perpendicular to the magnetic field at that location. You will find the transmitter at the intersection of those lines. [78.9% picked]
(B) Mark each measurement location on the map and draw lines connecting those measurements that are farthest apart. You will find the transmitter at the intersection of those lines. [2.5% picked]
(C) At each measurement location, draw a line that is parallel to the magnetic field at that location You will find the transmitter at the intersection of those lines. [10.9% picked]
(D) Mark each measurement location on the map and draw lines connecting all of them. You will find the transmitter at middle of that network of lines. [7.7% picked]
Answer: (A) At each measurement location, draw a line that is perpendicular to the magnetic field at that location. You will find the transmitter at the intersection of those lines. [78.9% picked]
Problem 11:
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. [48.6% picked]
(B) The spoon will become radioactive. [0.4% picked]
(C) Microwaves in the oven will cause electric currents to flow in the metal spoon. [51.1% picked]
(D) No microwaves will be able to form in the oven. [0.0% picked]
Answer: (C) Microwaves in the oven will cause electric currents to flow in the metal spoon. [51.1% picked]
Problem 12:
A junkyard uses a huge electromagnet to pick up old steel automobiles. That electromagnet only binds magnetically to steel when it is supplied with electricity. What is it about electricity that causes that attraction between the electromagnet and the steel?
(A) Electric currents produce magnetic fields. [82.3% picked]
(B) Electric charges are magnetic and produce magnetic fields. [12.7% picked]
(C) Differences in voltage produce magnetic field. [2.1% picked]
(D) Separated positive and negative charges produce magnetic fields. [2.8% picked]
Answer: (A) Electric currents produce magnetic fields. [82.3% picked]
Problem 13:
At each point in otherwise empty space, the electric field surrounding a negative charge is directed
(A) toward the negative charge and does not depend on the distance from the negative charge. [2.1% picked]
(B) away from the negative charge and does not depend on the distance from the negative charge. [0.0% picked]
(C) away from the negative charge and weakens with increasing distance from the negative charge. [10.2% picked]
(D) toward the negative charge and weakens with increasing distance from the negative charge. [87.7% picked]
Answer: (D) toward the negative charge and weakens with increasing distance from the negative charge. [87.7% picked]
Problem 14:
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. [25.4% picked]
(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. [35.6% picked]
(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. [16.5% picked]
(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. [22.5% picked]
Answer: (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. [35.6% picked]
Problem 15:
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. [91.2% picked]
(B) electrons in the steel are attracted to the permanent magnet's south magnetic pole. [1.1% picked]
(C) electrons in the steel are attracted to the permanent magnet's north magnetic pole. [0.4% picked]
(D) electric currents flow through the steel and those electric currents are magnetic. [7.4% picked]
Answer: (A) the permanent magnet's magnetic field causes the steel's magnetic domains to rearrange so that they attract the permanent magnet. [91.2% picked]
Problem 16:
The electric cord providing power to your desk lamp has two wires inside it. Your rocking chair crushes the cord while study and cuts through one of the cord's wires. That wire now has an insulating gap in it. Your desk lamp now emits
(A) twice as much light as before the wire was cut. [0.4% picked]
(B) no light. [97.9% picked]
(C) slightly less light than before the wire was cut. [1.1% picked]
(D) half as much light as before the wire was cut. [0.7% picked]
Answer: (B) no light. [97.9% picked]
Problem 17:
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. [40.5% picked]
(B) A current of 5 amperes flows through it and it consumes 2400 watts of electric power. [4.6% picked]
(C) A current of 2.5 amperes flows through it and it consumes 300 watts of electric power. [43.3% picked]
(D) A current of 10 amperes flows through it and it consumes 4800 watts of electric power. [11.6% picked]
Answer: (C) A current of 2.5 amperes flows through it and it consumes 300 watts of electric power. [43.3% picked]
Problem 18:
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. [13.4% picked]
(B) Your computer would receive approximately zero power and the cord would become hot. [78.2% picked]
(C) Your computer would operate properly, but the cord would become hot. [6.7% picked]
(D) The cord would remain cool, but your computer would become hot. [1.8% picked]
Answer: (B) Your computer would receive approximately zero power and the cord would become hot. [78.2% picked]
Problem 19:
A metal wire extends from left to right and current is flowing through it toward the right. Compare the voltage of the left part of the wire to the voltage on the right part of the wire.
(A) The voltage on the right is less than the voltage on the left. [70.1% picked]
(B) The voltage on the right is greater than the voltage on the left. [11.6% picked]
(C) The voltage on the right is closer to zero volts (0 volts) than is the voltage on the left. [6.0% picked]
(D) The voltages of the two parts are equal. [12.3% picked]
Answer: (A) The voltage on the right is less than the voltage on the left. [70.1% picked]
Problem 20:
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. [57.4% picked]
(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. [10.9% picked]
(C) The radio wave varies in height, moving up and down slightly, to represent fluctuations up and down in the music's air pressure. [21.5% picked]
(D) The radio wave's energy varies slightly between electric energy and magnetic energy to represent the music's air pressure fluctuations. [10.2% picked]
Answer: (A) The time interval between the radio wave's electric field peaks varies slightly to represent the music's air pressure variations. [57.4% picked]
Problem 21:
You are standing below a single electric wire that is carrying a constant current northward. At this moment, its voltage is +50,000 volts and the ground's voltage is 0 volts. In which direction is the electric field near you pointing?
(A) Northward [8.8% picked]
(B) Upward [10.6% picked]
(C) Downward [61.3% picked]
(D) Southward [19.4% picked]
Answer: (C) Downward [61.3% picked]
Problem 22:
You make a sharp left turn in your car and your cellphone slips off the dashboard and out the right passenger window. The cellphone exited the car because
(A) the dashboard of the turning car tilted sharply to become a ramp and the downhill ramp force pushed the cellphone out the window. [4.2% picked]
(B) the cellphone's weight pulled the cellphone out the window. [14.1% picked]
(C) the car did not exert enough leftward force on the cellphone to make the cellphone accelerate with the car. [67.3% picked]
(D) the car exerted a rightward centrifugal force on the cellphone that pushed the cellphone out the window. [14.4% picked]
Answer: (C) the car did not exert enough leftward force on the cellphone to make the cellphone accelerate with the car. [67.3% picked]
Problem 23:
You are standing on a skateboard in the middle of a bus and that bus is moving forward at constant velocity. The skateboard prevents the floor from exerting any horizontal forces on you. When you let go of the post you were holding, so that you experience no horizontal forces, you
(A) shift toward the front of the bus (in the direction of its velocity). [1.4% picked]
(B) shift toward the back of the bus (opposite its velocity). [33.8% picked]
(C) shift toward the side of the bus (perpendicular to the direction of its velocity). [0.4% picked]
(D) remain in the middle of the bus. [64.4% picked]
Answer: (D) remain in the middle of the bus. [64.4% picked]
Problem 24:
You are fidgeting while waiting for UVa to beat MSU. You throw a basketball upward and it rises for 2 seconds to a peak height of about 20 meters (66 feet) above your hand. After only 1 second of rising, how high above your hand was the ball?
(A) Approximately 15 meters [77.1% picked]
(B) Approximately 5 meters [14.8% picked]
(C) Approximately 10 meters [4.2% picked]
(D) Approximately 11 meters [3.9% picked]
Answer: (A) Approximately 15 meters [77.1% picked]
Problem 25:
The transformer in your garden illumination system 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 2-ampere alternating current flows through that primary coil, the transformer's secondary coil is supplying
(A) 10-volt AC power and 24 amperes flows through that secondary coil. [4.6% picked]
(B) 12-volt AC power and 24 ampere flows through that secondary coil. [8.5% picked]
(C) 10-volt AC power and 20 amperes flows through that secondary coil. [9.5% picked]
(D) 12-volt AC power and 20 amperes flows through that secondary coil. [77.5% picked]
Answer: (D) 12-volt AC power and 20 amperes flows through that secondary coil. [77.5% picked]
Problem 26:
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. [69.4% picked]
(B) repel. [19.4% picked]
(C) neither attract nor repel. [7.4% picked]
(D) attract. [3.9% picked]
Answer: (A) attract if they have opposite charges or repel if they have like charges. [69.4% picked]
Problem 27:
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. [5.3% picked]
(B) An electrically charged ball on top of a flagpole that is waving back and forth in the wind. [76.1% picked]
(C) An electrically charged ball that is traveling at constant velocity inside a glass elevator. [7.7% picked]
(D) An electrically charged ball that is traveling at constant velocity on top of a metal truck. [10.9% picked]
Answer: (B) An electrically charged ball on top of a flagpole that is waving back and forth in the wind. [76.1% picked]
Problem 28:
What characteristic distinguishes pure red light from pure blue light? A red light wave
(A) consists only of an electric field, while a blue light wave consists only of a magnetic field. [0.0% picked]
(B) has a larger magnetic field than a blue light wave. [3.5% picked]
(C) has a larger electric field than a blue light wave. [4.9% picked]
(D) has a smaller frequency than a blue light wave. [91.5% picked]
Answer: (D) has a smaller frequency than a blue light wave. [91.5% picked]
Problem 29:
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. [21.1% picked]
(B) attract. [12.7% picked]
(C) neither attract nor repel. [13.7% picked]
(D) attract, repel, or neither, depending on how their magnetic poles are positioned relative to one another. [52.5% picked]
Answer: (D) attract, repel, or neither, depending on how their magnetic poles are positioned relative to one another. [52.5% picked]
Problem 30:
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. [1.1% picked]
(B) Water molecules are polar (have an electric polarization), so microwaves exert fluctuating torques on them. [86.3% picked]
(C) Water molecules are charged (have a net electric charge), so microwaves exert fluctuating torques on them. [8.8% picked]
(D) Water molecules are polar (have an electric polarization), so microwaves exert fluctuating forces on them. [3.9% picked]
Answer: (B) Water molecules are polar (have an electric polarization), so microwaves exert fluctuating torques on them. [86.3% picked]
Video Discussion