PHYS 1060 Spring 2015

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.

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.

When you plug a toaster into a household electric outlet, the two metal blades of its plug connect with the two metal slots in the outlet. You start cooking toast and the outlet supplies 120-volt alternating current to the toaster. What is happening at those two connections?

(A) 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.

(B) The voltage difference between the two connections reverses many times per second, but the current flowing through each connection remains constant.

(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 toaster and zero current flows through the right connection. A fraction of a second later, current flows through the right connection to the toaster and zero current flows through the left connection. This arrangement of current flow to the toaster alternates back and forth many times per second.

A radio station's vertical transmitting antenna is located several miles west of you and there is nothing but open grassland between that antenna and you. As the radio wave from that antenna travels past you on its way eastward, in which directions do its electric and magnetic fields point?

(A) The electric field points east and west. The magnetic field points up and down.

(B) The electric field points north and south. The magnetic field points up and down.

(D) The electric field points up and down. The magnetic field points north and south.

For practical reasons, most AM radio stations have a single vertical transmitting antenna. If your AM radio receiver used a single rod-shaped metal receiving antenna, you would receive the transmission best by orienting that receiving antenna so that it is

(B) horizontal and points at a right-angle to the line between you and the transmitting antenna.

(D) horizontal and points away from the transmitting antenna.

Two pool balls are rolling forward on a horizontal table, but the green ball is traveling twice as fast as the red ball. The two balls roll off the edge of the table simultaneously. The green ball hits the ground

(A) after the red ball.

(B) at the same time as the red ball, but the green ball lands twice as far from the table as the red ball.

(D) at the same time as the red ball, but the green ball lands four times as far from the table as the red ball.

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.

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

(D) 1200 volt alternating current and the current in that coil is 100 amperes.

The microwave oven's cooking chamber has 6 sides. What are those sides made of?

(A) 5 sides are metal and 1 side is plastic mesh.

(B) 5 sides are plastic and 1 side is metal mesh.

(D) 5 sides are plastic and 1 side is plastic mesh.

Which force is your weight? [The force that is your weight and not a force that is equal to your weight.]

(A) The force you exert on a bathroom scale as you stand on that scale.

(B) The force that a bathroom scale exerts on you as you stand on that scale.

(D) The force you exert on a trampoline as you land on that trampoline after jumping high above the trampoline's surface.

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.

(D) become negative charge as a result of that move.

Electric power is transmitted long distances as a relatively small current at a relatively high voltage. Why is that arrangement used?

(A) Increasing the voltage difference between the wires reduces the resistance of those wires and causes their currents to decrease.

(B) Reducing the current in each wire reduces the resistances of those wires and causes their voltages to increase.

(C) Increase the voltage differences between the wires reduces the power wasted by those wires. Decreasing the current in those wires allows those large voltages to transmit large amounts of power.

(D) Decreasing the current in each wire reduces the power those wires consume. Increasing the voltage difference between the wires allows those small currents to transmit large amounts of power.

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.

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

If you put a magnetic compass in a uniform magnetic field, the compass needle will experience a

(A) torque unless the needle is aligned with the magnetic field or aligned opposite the magnetic field.

(B) torque no matter which way the needle is pointing.

(D) force in the direction opposite the magnetic field.

A coconut falls 20 meters from top of a tall palm tree to the ground. This fall takes about 2 seconds [assume the acceleration due to gravity is 10 m/s²]. After it has fallen for only 1 second, the coconut is still falling and is located

(A) 10 meters above the ground.

(B) considerably less than 10 meters above the ground.

(D) considerably more than 10 meters above the ground.

An electromagnet is a coil of wire that becomes magnetic due to electricity. What aspect of electricity makes it magnetic?

(A) Electric current is magnetic.

(B) Electric voltage is magnetic.

(D) Electric polarization is magnetic.

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.

(D) An electrically charged ball that is traveling at constant velocity inside a glass elevator.

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.

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

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.

(D) 1.5 volts, 3.0 volts, 12.0 volts, 13.5 volts, and 15.0 volts.

Your flashlight is switched on and a wire inside it is carrying current from the positive battery terminal to the lamp input. Compare the voltage at the positive battery terminal to the voltage at the lamp input.

(A) The voltage at the positive battery terminal is slightly less than the voltage at the lamp input.

(B) The voltage at the positive battery terminal is slightly greater than the voltage at the lamp input.

(D) The voltages at both the positive battery terminal and the lamp input are zero.

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

You are playing basketball and have managed to get your hands on the ball that an opponent is still holding. At this moment, the two of you are pulling the ball in opposite directions and you seem to be winning: the ball is moving toward you at constant velocity. At this moment, the net force on the ball

(A) points toward your opponent.

(B) points toward you.

(D) points straight down.

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.

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

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.

(D) The antenna needs to be long enough to accommodate the entire upward arrow of the radio wave's magnetic field.

A downhill skier is descending a snow-covered mountain. The skier steps off of a level region of the mountain and onto a steep slope. The skier begins to accelerate rapidly downhill on the slope. What force is causing the skier to accelerate downhill?

(A) The skier's weight.

(B) The support force exerted on the snow-covered slope by the skier.

(D) The downhill ramp force that is the sum of the skier's weight and the support force exerted on the skier by the snow-covered slope.

(A) The microwave has a smaller frequency than the radio wave.

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

(D) The microwave has a weaker electric field than the radio wave.

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.

(D) both pieces have net south pole.

You accidently pinch the cord of your desk lamp under your rocking chair and cut through one of the two wires in the lamp's cord. Only one wire now connects the lamp to the electric socket. If you switch on the lamp,

(A) the normal amount of current will flow through the lamp, but only half as often, so the lamp will glow at half its normal brightness.

(B) no current will flow through either wire and the lamp will remain dark.

(C) 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.

(D) the normal amount of current will flow through the one remaining wire and the lamp will glow at half its normal brightness.

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.

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

A set of high tension power lines are conveying several million watts of electric power to Charlottesville. Near those power lines, there are

Physics 1060 - Spring 2015 - Midterm Exam 2 - Posted Version