PHYS 1060 Midterm Exam 2, Spring 2011

Problem 1:

The sky is blue rather than red because the atmosphere scatters blue light more effectively than red light. Blue light scatters more than red light because blue light has

(A) shorter wavelengths than red light.
(B) a higher temperature than red light.
(C) lower frequencies than red light.
(D) a lower temperature than red light.

Problem 2:

Your hairdryer was designed to operate on 120 volt alternating current, but you are traveling in Europe and your friend connects it to 230 volt alternating current. The hairdryer quickly burns out because

(A) the correct amount of current flows through the hairdryer's 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 hairdryer's heating element, but that current alternates too rapidly and overheats the heating element.
(C) the voltage gradient in the hairdryer's 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 hairdryer was designed to handle and it burns up the hairdryer.

Problem 3:

Light's speed in Pyrex glass is the same as its speed in salad oil. Suppose you fill a Pyrex measuring cup with salad oil and place it in the sun. When a ray of sunlight passes from the Pyrex glass and enters the salad oil, will that ray partially reflect from the interface between glass and oil, and will the ray's path bend (refract) as it moves from glass to oil?

(A) The ray will not partially reflect and its path will not bend.
(B) The ray will partially reflect and its path will bend.
(C) The ray will partially reflect and its path will not bend.
(D) The ray will not partially reflect and its path will bend.

Problem 4:

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 switch on the lamp,

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

Problem 5:

Red light travels slightly faster in water than does violet light. In a rainbow, red appears on the outside of the arc and violet appears on the inside of the arc. If red light instead traveled slower in water than did violet light, how would the colors of a rainbow be arranged?

(A) The colors would be the same: red on the outside and violet on the inside.
(B) The colors would be reversed: violet on the outside and red on the inside.
(C) The colors would be rearranged: violet in the middle of the arc and red on both the inside and outside.
(D) The colors would be rearranged: red in the middle of the arc and violet on both the inside and outside.

Problem 6:

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 rotor's poles as they approach and attract the rotor's poles as they separate.
(B) attract the rotor's poles as they approach and repel the rotor's poles as they separate.
(C) repel the rotor's poles as they approach and attract the rotor's poles as they separate.
(D) repel the rotor's poles as they approach and repel the rotor's poles as they separate.

Problem 7:

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) An electric current will flow through it, heating it up, and electric charge will also spray out of its sharp ends.
(B) An electric current will flow through it, heating it up, but no charge will leave the wire.
(C) The twist tie will not be affected by the microwaves because it contains no water.
(D) The twist tie will remain cool, but electric charge will spray out of its sharp ends.

Problem 8:

The transformer in a power adapter 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 amperes is flowing through that secondary coil.
(B) 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.
(D) 10 volt AC power and a current of 10 amperes is flowing through that secondary coil.

Problem 9:

The voltage at the start of an ordinary wire is 20 volts and a current of 1 ampere enters that wire. The voltage at the end of the wire is

(A) more than 20 volts and a current of less than 1 ampere exits the wire.
(B) less than 20 volts and a current of 1 ampere exits the wire.
(C) 20 volts and a current of 1 ampere exits the wire.
(D) more than 20 volts and a current of 1 ampere exits the wire.

Problem 10:

The electric field near a positive charge points

(A) away from the charge and does not depend on the distance from the charge.
(B) toward the charge and becomes weaker with increasing distance from the charge.
(C) toward the charge and does not depend on the distance from the charge.
(D) away from the charge and becomes weaker with increasing distance from the charge.

Problem 11:

When an alternating current flows through the primary coil of a transformer, the magnetization of the transformer's iron core reverses rapidly. That changing magnetization can provide power to current in the transformer's secondary coil by

(A) producing an electric field that can do work on charges 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.

Problem 12:

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 gate surface can allow the MOSFET to conduct current by

(A) attracting electrons into the channel, where they fill some of the conduction levels.
(B) pushing positive charge out of the channel, where that positive charge had been blocking the flow of electric current.
(C) attracting electrons into the channel, so that the valence levels are then completely filled and the conduction levels are completely empty.
(D) bending the channel toward the gate surface and removing the kink that had been pinching off the flow of electric current.

Problem 13:

You are listening to a weak radio station as you walk through a city. You find that the reception depends on your location and that occasionally you get remarkably good reception. How are the structures around you acting to give you better reception than you would get if those structures weren't there?

(A) The iron in those structures is amplifying the radio wave from the station, strengthening its electric field.
(B) The structures are slowing the radio wave, giving your receiver more time to gather the wave with its antenna.
(C) The iron in those structures is amplifying the radio wave from the station, strengthening its magnetic field.
(D) Portions of the radio wave that reflect from those structures are producing constructive interference at the antenna of your radio receiver.

Problem 14:

A motor/generator is a single device that can act as a motor or a generator. Suppose that you are twisting the rotor of a motor/generator with your hand while that rotor is rotating. The device acts as a generator when you

(A) twist the rotor counterclockwise.
(B) twist the rotor in the direction opposite its rotation.
(C) twist the rotor in the direction of its rotation.
(D) twist the rotor clockwise.

Problem 15:

When 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.

Problem 16:

You are boating on a vast lake and listening to an AM radio station. You can see the station's vertical transmitting antenna on the shore, directly to your west. As that station's 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.

Problem 17:

Which one of the following objects emits an electromagnetic wave that travels across the universe?

(A) An electrically charged ball that is traveling at constant velocity inside a glass elevator.
(B) An electrically charged ball that is traveling at constant velocity on top of a metal truck.
(C) An electrically charged ball that is motionless at the top of a tall metal building.
(D) An electrically charged ball that is going around in a circle at a constant speed on a plastic merry-go-round.

Problem 18:

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.

Problem 19:

You are standing on a cliff at the edge of a lake and dropping pebbles into the water. Each pebble takes 2 seconds to reach the water. After it has fallen for only 1 second, one of these pebbles is located

(A) about midway between you and the water.
(B) a few inches closer to you than to the water.
(C) much closer to the water than to you.
(D) much closer to you than to the water.

Problem 20:

You have two bowling balls, one of which weighs twice as much as the other. The balls roll off a horizontal table at the same time, but the heavier ball leaves the table at twice the velocity of the lighter ball. In this situation, both balls hit the floor

(A) at approximately the same time, but the lighter ball hits considerably farther from the table than the heavier ball.
(B) at approximately the same time and at the same distance from the table.
(C) at approximately the same distance from the table, but the heavier ball hits the floor well before the lighter ball.
(D) at approximately the same time, but the heavier ball hits considerably farther from the table than the lighter ball.

Problem 21:

The positive terminal and negative terminal of a 9 volt battery are about 1/4 inch apart. In keeping with its name, the battery's positive terminal has a voltage that is 9 volts greater than the voltage of its negative terminal. Midway between those two terminals, the electric field

(A) is 4.5 volts.
(B) points away from the positive terminal and toward the negative terminal.
(C) is zero.
(D) points toward the positive terminal and away from the negative terminal.

Problem 22:

Running on soft dry sand is exhausting, so you switch to running on hard wet sand. The hard wet sand takes less energy from you because

(A) it doesn't move downward as you push downward on it, so you do almost zero work on it.
(B) it stops the downward motion of your foot faster and thus absorbs less of your momentum.
(C) it pushes up on your foot just as hard as your foot pushes on it, unlike the soft dry sand.
(D) its water content gives it more mass and that prevents it from absorbing energy.

Problem 23:

The voltage difference between the two ends of a metal wire is proportional to

(A) one divided by the current passing through that wire.
(B) one divided by the net charge of that wire.
(C) the net charge of that wire.
(D) the current passing through that wire.

Problem 24:

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.

Problem 25:

A microwave heats food primarily through the food's water. Liquid water heats up when exposed to intense an 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 currents 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.

Problem 26:

The difference between a 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 its electrons to cross the mid-point 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.

Problem 27:

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 and negative charges, while a direct current delivers only positive charges. That difference makes alternating current twice as efficient as direct current.
(D) an alternating current carries more electric power than a direct current.

Problem 28:

A typical gasoline-powered home generator has two electric outlets: one that provides 120 volt alternating current and one that provides 240 volt alternating current. Each outlet is connected to a coil of wire in the generator, a coil that resembles the secondary coil of a transformer. Compared to the coil supplying the 120 volt outlet, the coil supplying the 240 volt outlet

(A) uses wire that is half as heavy and has twice the electrical resistance.
(B) half as many turns around the iron core of the generator.
(C) makes twice as many turns around the iron core of the generator.
(D) uses wire that is twice as heavy and has half the electrical resistance.

Problem 29:

Two of your friends are pulling on opposite ends of a rope in the game of tug-o-war. At this moment, your friend on the left is winning: both of them are moving to the left at constant velocity. The net force on the rope

(A) points straight down.
(B) is zero.
(C) points toward the left.
(D) points toward the right.

Problem 30:

Unlike pure semiconductor, n-type semiconductor has some filled conduction levels and p-type semiconductor has some empty valence levels. Suppose you have two electrically neutral disks, one of n-type semiconductor and one of p-type semiconductor. When you touch the two disks, electrons migrate from the

(A) n-type semiconductor to the p-type semiconductor and the resulting electric field points from the p-type semiconductor toward the n-type semiconductor.
(B) n-type semiconductor to the p-type semiconductor and the resulting electric field points from the n-type semiconductor toward the p-type semiconductor.
(C) p-type semiconductor to the n-type semiconductor and the resulting electric field points from the n-type semiconductor toward the p-type semiconductor.
(D) p-type semiconductor to the n-type semiconductor and the resulting electric field points from the p-type semiconductor toward the n-type semiconductor.