PHYS 1060 Spring 2012

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.

(D) collides with an atom in the diode's gas discharge and causes that atom to emit an electromagnetic wave.

You toss a grapefruit straight up. Disregarding any effects of due to the air, what force or forces are acting on the grapefruit while it is above your hands?

(A) Its weight along with a steadily decreasing upward force.

(B) Its weight along with an upward force that steadily decreases until the grapefruit reaches its highest point. After that point, there is only the constant downward force of gravity.

(D) A steadily decreasing upward force from the moment it leaves your hands until it reaches its highest point and then a steadily increasing downward force as the grapefruit returns toward your hands.

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.

(D) Electric voltage is magnetic.

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.

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

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.

(D) a semiconductor.

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.

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

(D) 1 part in 100,000.

You are at the gym, exercising on a step machine. You have one foot on each of the machine's pedals and you move those pedals up and down as you step. The pedals always push upward on your feet, but they push harder while moving downward than while moving upward. When during this exercise is your foot transferring energy to the pedal that it is touching?

(A) As that pedal moves upward.

(B) As that pedal moves downward.

(D) When that pedal is accelerating.

A typical radio wave that is traveling from Charlottesville to Richmond has a vertical electric field and horizontal magnetic field. Suppose we used some filtering system to eliminate the wave's magnetic field, but made no effort to get rid of its electric field. What would happen to the wave?

(A) The wave would affect only vertical antennas in Richmond; without its horizontal magnetic field it would no longer be able to affect horizontal antennas.

(B) The wave could not exist without its magnetic field.

(D) The wave's polarization would change from horizontal to vertical.

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.

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

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

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.

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

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 north. As that station's radio wave passes by you, its electric field points

(A) horizontally east and west and its magnetic field points horizontally north and south.

(B) horizontally north and south and its magnetic field points horizontally east and west.

(D) vertically up and down and its magnetic field points horizontally north and south.

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.

(D) short-circuit light waves that have the wrong wavelengths and absorb their energies.

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.

There are two electrically charged coins on your desk. Although the coins have equal amounts of charge, the left coin's charge is positive and the right coin's charge is negative. Which statement correctly describes the electric field near those coins?

(A) Between the coins, the electric field points to the right. To left of the left coin, the electric field points right. To the right of the right coin, the electric field points right.

(B) Between the coins, the electric field points to the left. To left of the left coin, the electric field points left. To the right of the right coin, the electric field points left.

(C) Between the coins, the electric field points to the left. To left of the left coin, the electric field points right. To the right of the right coin, the electric field points right.

(D) Between the coins, the electric field points to the right. To left of the left coin, the electric field points left. To the right of the right coin, the electric field points left.

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 across the boundary between the disks and each disk becomes electrically charged. An electric field appears between the two disks. During the migration, electrons move from the

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

When sunlight passes through a properly cut diamond, the diamond sparkles with light and color. How does the diamond manage to separate the colors of light in white sunlight?

(A) Different frequencies of light travel at different speeds in the diamond and they refract differently as they enter and exit the diamond.

(B) Light waves experience interference as they reflect off the surfaces of the diamond and different wavelengths of light interfere differently.

(D) Different wavelengths of light polarize differently in the diamond and break into colors.

(A) one divided by the voltage difference between the two ends of the wire.

(B) one divided by the net charge of that wire.

(D) the net charge of that wire.

You are wading in a shallow pond and see a shiny ring on the lake bottom in front of you. You reach for the ring, but discover that it is not exactly where it appears to be. In fact, the portion of your arm that's under water is bent relative to the portion of your arm that's above water. What effect is causing these optical problems?

As a camera takes a photograph of a bird, many different light rays from the tip of the bird's beak pass through the camera's lens. Assuming the camera is properly focused on the bird's beak, those light rays will

(A) converge to one point on the camera's image sensor.

(B) travel parallel to one another as they approach the camera's image sensor.

(D) illuminate the entire image sensor of the camera.

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.

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.

The sign in the window of a diner is made from glass tubes that glow various colors as electric current passes through them. Those tubes are actually fluorescent lamps, but instead of emitting white light, they emit colored light. What change did the lamp manufacturer make to produce a green fluorescent lamp instead of a white one?

(A) They increase the current flowing through the lamp's gas discharge.

(B) They reduce the current flowing through the lamp's gas discharge.

(D) They replaced the mercury gas in the lamp with chlorine gas.

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.

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.

(D) a wide light wave and the laser pointer emits a narrow light wave.

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) 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.

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

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.

(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.

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.