PHYS 1060 Spring 2010 - Final Exam

(Some day, I hope to film the video solutions. At present, I just don't have time. -- Lou Bloomfield 5/8/2012)

You are throwing a ball straight up and then catching it as it returns to your hand. When the ball leaves your hand, its momentum is in the upward direction but when it returns to your hand, its momentum is in the downward direction. During its flight above your hand, what happens to the ball's initial upward momentum?

(A) The upward momentum is converted into thermal energy. [0.4% picked]

(B) The upward momentum is transferred to the earth. [63.9% picked]

(D) The upward momentum is converted into gravitational potential energy. [30.3% picked]

Cheap stainless steel forks bend easily because they are made from “austenitic” stainless steel—stainless steel that is in steel's high-temperature crystalline form even at room temperature. These forks cannot be hardened with carbon and heat treatment because carbon

(A) burns during heat treatment. [15.4% picked]

(B) spoils the stainless nature of the steel. [28.2% picked]

(D) reacts with austenitic stainless steel to form a gas. [7.9% picked]

You have just finished drying your clothes and a sock is clinging to shirt. As you pull the sock away from the shirt, using insulating gloves, the voltage difference between those items will

(A) increase. [54.4% picked]

(B) remain unchanged, but the net charge on each item will decrease. [11.2% picked]

(D) remain unchanged and the net charge on each item will remain unchanged. [6.6% picked]

You kick a soccer ball forward and it travels past the goalkeeper and into the goal! After the soccer ball left your foot and was traveling toward the goal, it was experiencing

(A) a forward horizontal force until it reached the midpoint of its trip into the goal and then a backward horizontal force for the remainder of its trip. [0.0% picked]

(B) no horizontal force in the forward direction. [97.1% picked]

(D) a forward horizontal force that remained constant all the way to the goal. [1.7% picked]

A magnifying glass held in sunlight forms a round spot that can burn paper. What spot(s) will form if you hold that lens in light from the lamps overhead?

(A) A round spot, but much smaller than the one formed when you use sunlight. [3.7% picked]

(B) A round spot, just like the one formed when you use sunlight. [3.7% picked]

(D) Spots that look exactly like the overhead lamps. [80.9% picked]

If you put a steel marble into a microwave oven, along with a bowl of raw broccoli, and turn the oven on at full power for a minute, the most likely result is that

(A) almost nothing will have happened to the marble and the broccoli will be partly cooked. [86.3% picked]

(B) sparks will leap out of the marble and may burn the nearby broccoli. [5.4% picked]

(D) the magnetron will burn out and the microwave will stop working altogether. [1.7% picked]

Answer: (A) almost nothing will have happened to the marble and the broccoli will be partly cooked. [86.3% picked]

You are sitting in a hotel restaurant, watching your friend ride a glass elevator upward from the 1st floor to the 5th floor. He is holding a heavy package in his hands. From your perspective, he is doing

(A) zero work on the package because he is not using his muscles. [4.1% picked]

(B) positive work on the package. [90.9% picked]

(D) negative work on the package. [0.8% picked]

A thermal fission nuclear reactor can operate using natural or slightly enriched uranium because it uses a technique that makes the presence of uranium-238 nuclei unimportant. The reactor uses a moderator to

(A) slow the fission neutrons down so that they interact only with uranium-235. [81.7% picked]

(B) make hydrogen, which then experiences fusion to form helium. [1.2% picked]

(C) heat the uranium up so that the uranium-238 turns into a gas and does not interact with fission neutrons. [5.0% picked]

(D) heat the uranium up so that it undergoes fission more easily. [8.3% picked]

Answer: (A) slow the fission neutrons down so that they interact only with uranium-235. [81.7% picked]

The car you are driving skids off the road in bad weather and collides with a tree head on. Fortunately, the airbag inflates and protects your head from injury. By coming to a stop in the airbag instead of on the steering wheel, your head transferred

(A) the same amount of momentum to the car but over a longer period of time and with a smaller force. [97.9% picked]

(B) the same amount of momentum to the car in the same period of time but with a smaller force [0.4% picked]

(D) more momentum to the car but with a smaller force. [0.4% picked]

Answer: (A) the same amount of momentum to the car but over a longer period of time and with a smaller force. [97.9% picked]

In a fission chain reaction, fragments produced when one nucleus fissions go on to induce other nuclei to fission. The nuclear fragments that are most likely to induce other fissions are

(A) neutrons. [78.4% picked]

(B) alpha particles (helium nuclei). [2.9% picked]

(D) electrons. [14.9% picked]

Two identical children run along a horizontal platform side by side and jump into a swimming pool at the same moment. They both jump equally hard, but one child jumps upward while the other child jumps forward. You watch them fall and see that

(A) the two children reach the water at the same moment and at the same distance from the pool's edge. [0.4% picked]

(B) the child who jumped upward reaches the water before the child who jumped forward. [0.4% picked]

(C) the two children reach the water at the same moment and but the child who jumped forward travels farther from the pool's edge than does the other child. [8.7% picked]

(D) the child who jumped forward reaches the water before the child who jumped upward. [90.5% picked]

Answer: (D) the child who jumped forward reaches the water before the child who jumped upward. [90.5% picked]

You are listening to an AM radio station while sailing your sailboat in the Atlantic Ocean. You can see the station's vertical transmitting antenna 10 miles to your west. 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. [3.7% picked]

(B) vertically up and down and its magnetic field points horizontally north and south. [43.2% picked]

(D) horizontally north and south and its magnetic field points horizontally east and west. [2.9% picked]

Answer: (B) vertically up and down and its magnetic field points horizontally north and south. [43.2% picked]

You are competing in a dog-sled race and the dogs are pulling you and your sled forward in a straight line at a steady pace. Which of the following statements about the forces acting on you and the sled is correct?

(A) The amount of forward force that the dogs are exerting on you and the sled must be greater than the amount of the downward weight of you and the sled. [1.7% picked]

(B) The amount of forward force that the dogs are exerting on you and the sled must be greater than the amount of backward force that friction is exerting on you and the sled. [7.9% picked]

(C) If the dogs were to exert twice as much force on you and the sled, you would move forward twice as fast. [2.9% picked]

(D) The amount of forward force that the dogs are exerting on you and the sled must be equal to the amount of backward force that friction is exerting on you and the sled. [86.7% picked]

Answer: (D) The amount of forward force that the dogs are exerting on you and the sled must be equal to the amount of backward force that friction is exerting on you and the sled. [86.7% picked]

A person who is "nearsighted" sees nearby objects clearly but can't focus on a distant landscape. That landscape appears blurry because each eye forms its real image in front of the retina. To move the real image of the landscape away from the lens so that its image forms on the retina, the person should wear eyeglasses that contain

(A) low f-number converging lenses. [1.2% picked]

(B) long-focal length converging lenses. [21.2% picked]

(D) diverging lenses. [63.9% picked]

Natural rubber is the dried sap of certain tropic trees. If you heat natural rubber in the oven, it becomes a liquid and you can pour it like syrup. However, at room temperature natural rubber is elastic: it returns to its original shape after you stretch it. What feature of natural rubber determines its original shape?

(A) The chemical bonds in its polymer chains. [16.6% picked]

(B) The entanglements of its polymer chains. [67.2% picked]

(D) Its molecular structure. [7.1% picked]

The constituents of a radioactive nucleus are in stable equilibrium, yet they eventually rearrange in a way that allows the nucleus to fall apart and release stored energy. What allows the nucleus to escape from its stable equilibrium and subsequently fall apart?

(A) The laws of thermodynamics. [5.8% picked]

(B) The laws of motion. [2.5% picked]

(D) The wave nature of matter (quantum physics). [75.9% picked]

A DVD-player uses a lens to focus a red laser beam onto a layer of metal in the DVD. The size of the illuminated spot on the metal is about 500 nanometers in diameter (500 billionths of a meter) because

(A) a more tightly focused laser beam will melt the plastic near the metal layer. [6.6% picked]

(B) that is as small a spot as the wave-character of the laser light will allow. [70.5% picked]

(D) surface features on the metal layer cannot be made smaller than about 500 nanometers. [17.4% picked]

Answer: (B) that is as small a spot as the wave-character of the laser light will allow. [70.5% picked]

An optical communication fiber can carry light for miles with almost no loss of intensity. Light travels through the fiber's glass core and that core is coated with

(A) a different glass in which light travels slower than in the core. [32.0% picked]

(B) a different glass in which light travels faster than in the core. [55.2% picked]

(D) a thin layer of pure silver. [1.7% picked]

Answer: (B) a different glass in which light travels faster than in the core. [55.2% picked]

An electrically charged ball emits an electromagnetic wave that travels across the universe when it is

(A) motionless at the top of a tall metal building. [3.3% picked]

(B) traveling at constant velocity on top of a metal truck. [7.1% picked]

(D) going around in a circle at a constant speed on a plastic merry-go-round. [81.7% picked]

Answer: (D) going around in a circle at a constant speed on a plastic merry-go-round. [81.7% picked]

(A) the crosslinked polymers are kept from reptating (moving along their length) even as temperature is increased. [62.2% picked]

(B) the polymers in tires have been crystallized, which causes them to burn before they melt. [14.5% picked]

(C) rubber is made of tree-like polymers that can't reptate (move along their length) the way chain-like polymers can. [10.8% picked]

(D) the polymer molecules in rubber are just too long to reptate (move along their length). [8.7% picked]

Answer: (A) the crosslinked polymers are kept from reptating (moving along their length) even as temperature is increased. [62.2% picked]

(A) it has a much higher frequency than normal visible light. [7.1% picked]

(B) it consists of a great many identical photons. [84.6% picked]

(D) it is much brighter than normal visible light. [2.9% picked]

You have two bowling balls, one of which weighs twice as much as the other. The balls roll off a horizontal table simultaneously and in the same direction, but the lighter ball is traveling twice as fast as the heavier ball when they lose contact with the table. In this situation,

(A) the heavier ball hits the floor much sooner than the lighter ball, but the lighter ball hits the floor considerably farther from the table than the heavier ball. [4.6% picked]

(B) the heavier ball hits the floor much sooner than the lighter ball, but both balls land at approximately the same distance from the table. [1.2% picked]

(C) both balls hit the floor approximately simultaneously, but the lighter ball hits the floor considerably farther from the table than the heavier ball. [90.5% picked]

(D) both balls hit the floor approximately simultaneously, but the heavier ball hits the floor considerably farther from the table than the heavier ball. [3.7% picked]

Answer: (C) both balls hit the floor approximately simultaneously, but the lighter ball hits the floor considerably farther from the table than the heavier ball. [90.5% picked]

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) bending the channel toward the gate surface and removing the kink that had been pinching off the flow of electric current. [0.4% picked]

(B) attracting electrons into the channel, where they fill some of the conduction levels. [80.5% picked]

(C) pushing positive charge out of the channel, where that positive charge had been blocking the flow of electric current. [6.6% picked]

(D) attracting electrons into the channel, so that the valence levels are then completely filled and the conduction levels are completely empty. [12.4% picked]

Answer: (B) attracting electrons into the channel, where they fill some of the conduction levels. [80.5% picked]

You immerse a colorless glass marble in a bowl of colorless salad oil. Light travels at exactly the same speed in the glass marble as it does in the salad oil. While the marble is in the oil,

(A) you cannot see the marble at all. [95.4% picked]

(B) you see a real image formed by the marble. [0.8% picked]

(D) you see a virtual image formed by the marble. [2.9% picked]

Cobalt-60 is a radioactive isotope of cobalt. Suppose you put 1,000,000 cobalt-60 atoms in a jar. After waiting 5 years, you examine the jar and find that it contains approximately 500,000 cobalt-60 atoms. After waiting another 5 years, you examine the jar again and find that it contains

(A) slightly less than 500,000 cobalt 60-atoms. [0.8% picked]

(B) approximately 0 cobalt-60 atoms. [3.3% picked]

(D) approximately 500,000 cobalt 60-atoms. [1.2% picked]

An acorn falls 20 meters from the high branch of an oak tree to the ground. This fall takes about 2 seconds. After it has fallen for only 1 second, the acorn is still falling and is located

(A) somewhat more than 10 meters above the ground. [71.0% picked]

(B) approximately 15 meters above the ground. [23.7% picked]

(D) 10 meters above the ground. [2.1% picked]

(A) higher voltage to lower voltage and through the iPod's electronics from lower voltage to higher voltage. [8.3% picked]

(B) higher voltage to lower voltage and through the iPod's electronics from higher voltage to lower voltage. [5.8% picked]

(C) lower voltage to higher voltage and through the iPod's electronics from lower voltage to higher voltage. [0.8% picked]

(D) lower voltage to higher voltage and through the iPod's electronics from higher voltage to lower voltage. [84.6% picked]

Answer: (D) lower voltage to higher voltage and through the iPod's electronics from higher voltage to lower voltage. [84.6% picked]

A thief can sometimes break a steel padlock by chilling it with liquid nitrogen and then striking it with a hammer. Padlock steel is normally very tough, meaning that you must do lots of work on it before it breaks. But cooling steel can spoil its toughness because at very low temperatures,

(A) the steel crystallizes and is then unable to undergo slip or plastic deformation. [31.1% picked]

(B) becomes magnetized and its opposite poles repel and push it apart. [0.8% picked]

(D) dislocations can't move through steel to assist slip and permit permanent deformation. [63.5% picked]

Answer: (D) dislocations can't move through steel to assist slip and permit permanent deformation. [63.5% picked]

If you hold a strong permanent magnet inside a metal ring and then yank the magnet out of the ring, you will create an electric field in the metal ring and an electric current will flow through that ring. If you yank the magnet out of a glass ring, no current will flow through the glass ring because

(A) the glass ring is made from a non-magnetic material. Since no magnetic fields can be present inside the ring, removing the magnet has no effect on the ring. [20.7% picked]

(B) although you will create an electric field in the glass ring, the glass ring has no mobile electric charges to carry an electric current. [73.9% picked]

(C) the glass ring creates its own magnetic field in the opposite direction and cancels out the electromagnetic effects. [0.4% picked]

(D) removing the magnet from the glass ring does not create an electric field. [4.1% picked]

Answer: (B) although you will create an electric field in the glass ring, the glass ring has no mobile electric charges to carry an electric current. [73.9% picked]

Consider (1) the microwave from a cell phone, (2) the light from a laser pointer, and (3) the beam from a flashlight. Of these three, which one(s) exhibit strong interference effects after reflecting from an assortment of metal surfaces?

(A) 2 and 3, but not 1. [10.8% picked]

(B) 1, 2, and 3. [6.6% picked]

(D) 1 and 2, but not 3. [60.2% picked]

(A) an alternating current carries more electric power than a direct current. [6.6% picked]

(B) 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. [2.9% picked]

(C) transformers can move power from one circuit to another only if those circuits are carrying alternating current. [83.8% picked]

(D) alternating current is less likely to cause an electrical fire than direct current. [5.0% picked]

Answer: (C) transformers can move power from one circuit to another only if those circuits are carrying alternating current. [83.8% picked]

On a clear day, the sky appears blue because some visible light from the sun experiences Rayleigh scattering. But sunlight also contains infrared and ultraviolet light. Does Rayleigh scattering affect them significantly?

(A) Both ultraviolet and infrared lights are strongly affected. [6.6% picked]

(B) Both ultraviolet and infrared lights are barely affected. [30.3% picked]

(D) Ultraviolet light is strongly affected, but infrared light is barely affected. [42.7% picked]

Answer: (D) Ultraviolet light is strongly affected, but infrared light is barely affected. [42.7% picked]

When you use a telephoto lens to take a picture of a distant object, that object appears larger in the final photograph than it would with a wide angle lens. The difference between a telephoto lens and a wide angle lens is that the telephoto lens has a

(A) larger diameter than the wide angle lens. [6.6% picked]

(B) smaller diameter than the wide angle lens. [10.4% picked]

(D) shorter focal length than the wide angle lens. [22.8% picked]

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. [5.4% picked]

(B) a motor. [0.4% picked]

(C) 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. [68.0% picked]

(D) 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. [25.7% picked]

Answer: (C) 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. [68.0% picked]

The color of a high-pressure sodium discharge lamp is yellow when you first turn it on, but it gradually becomes whiter as it warms up. Why does its light become whiter?

(A) As the sodium atoms become hotter, the peak of their black-body spectrum shifts toward the blue end of the spectrum and the color of the lamp becomes less like candlelight and more like sunlight. [32.0% picked]

(B) As the sodium atoms become hotter, their quantum structures change and their electrons no longer reside in specific orbitals. [5.4% picked]

(C) As the lamp becomes hotter, the speed at which light travels through it becomes more uniform and refraction no longer separates out the yellow light. [10.8% picked]

(D) As the sodium pressure increases, collisions between atoms broaden their spectrum and the original yellow light becomes trapped in the dense sodium vapor. [48.5% picked]

Answer: (D) As the sodium pressure increases, collisions between atoms broaden their spectrum and the original yellow light becomes trapped in the dense sodium vapor. [48.5% picked]

Your computer has several LEDs (light-emitting diodes), some of which emit red light and some of which emit green light. What is the difference between them?

(A) The green LEDs have smaller band gaps than the red LEDs. [23.2% picked]

(B) The green LEDs have larger band gaps than the red LEDs. [63.9% picked]

(D) The green LEDs have less current flowing through them than the red LEDs. [4.1% picked]

Answer: (B) The green LEDs have larger band gaps than the red LEDs. [63.9% picked]

(A) is motionless and horizontal. [2.9% picked]

(B) has an angular velocity that is constant. [86.7% picked]

(D) has an angular velocity that is gradually decreasing toward zero. [0.8% picked]

Your hairdryer was designed to operate on 120 volt alternating current, but you are traveling in another country and your friend connects it to 240 volt alternating current. The hairdryer quickly burns out. Doubling the voltage supplied to the hairdryer's heating element caused

(A) the voltage it consumed to double and the power it consumed to double. [5.8% picked]

(B) the power it consumed to double, although the current in it remained unchanged. [19.5% picked]

(D) the current in it to double and the power it consumed to quadruple. [61.4% picked]

Answer: (D) the current in it to double and the power it consumed to quadruple. [61.4% picked]

You are looking into the front window of an aquarium full of fish. You suddenly realize that the two side walls appear to be perfectly reflecting, so that light from behind the aquarium is perfectly reflected back toward your eyes in front of the aquarium. This effect, where light bounces perfectly from the outer layer of glass when it tries to get out of the glass at a shallow angle is an example of total internal reflection, which occurs when

(A) the speed of light in the material drops to exactly 1/2 its value in air and the light reflects from it perfectly. [3.7% picked]

(B) the refractive index of the glass becomes infinite and light reflects from it perfectly. [6.6% picked]

(C) light undergoes such extreme refraction as it tries to leave a material that it bends back into the material and doesn't escape at all. [88.0% picked]

(D) light encountering a surface produces mobile electrons in that surface that make it metallic. The metalized surface then reflects the light perfectly. [1.2% picked]

Answer: (C) light undergoes such extreme refraction as it tries to leave a material that it bends back into the material and doesn't escape at all. [88.0% picked]

(A) different colors of light travel at different speeds in the soap film. [50.2% picked]

(B) of absorption of certain colors in the soap film. [0.4% picked]

(D) of interference between the front and back reflections from the soap film. [48.5% picked]

Answer: (D) of interference between the front and back reflections from the soap film. [48.5% picked]

The microscope structure of quartz glass (amorphous quartz) closely resembles that of

(A) steel. [12.4% picked]

(B) crystalline quartz (quartz crystals or quartz sand). [29.5% picked]

(D) molten quartz (liquid quartz). [46.1% picked]

The faster a radio station shifts the charge on its antenna from positive to negative and back again, the

(A) higher the frequency of its radio wave and the shorter the wavelength of that wave. [92.1% picked]

(B) higher the frequency of its radio wave and the longer the wavelength of that wave. [4.1% picked]

(D) lower the frequency of its radio wave and the shorter the wavelength of that wave. [2.1% picked]

Answer: (A) higher the frequency of its radio wave and the shorter the wavelength of that wave. [92.1% picked]

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) 40 amperes flows through the wires of your home and wastes 2 watts in those wires. [1.2% picked]

(B) 10 amperes flows through the wires of your home and wastes 2 watts in those wires. [6.2% picked]

(D) 20 amperes flows through the wires of your home and wastes 4 watts in those wires. [70.5% picked]

Answer: (D) 20 amperes flows through the wires of your home and wastes 4 watts in those wires. [70.5% picked]

Compared to an ordinary alkaline AA battery, an ordinary alkaline D battery provides

(A) a larger voltage rise but can supply the same total electrical energy. [6.6% picked]

(B) a larger voltage rise and can supply more total electrical energy. [6.2% picked]

(D) the same voltage rise and can supply the same total electrical energy. [0.8% picked]

Answer: (C) the same voltage rise but can supply more total electrical energy. [85.5% picked]

A xerographic copier uses a very thin wire with a large positive voltage to spray electric charges onto the surface of its photoconductor. That thin wire

(A) heats up quickly and boils off electric charge onto the surface of the photoconductor. [1.7% picked]

(B) is able to move charge quickly enough to produce finely detailed light and dark spots on the copies. [6.6% picked]

(C) has a strong electric field near it and that strong field pushes charge from the wire onto air molecules. [77.2% picked]

(D) has a weak electric field near it and that weak field easily permits the transfer of charge from the wire to surface of the photoconductor. [13.7% picked]

Answer: (C) has a strong electric field near it and that strong field pushes charge from the wire onto air molecules. [77.2% picked]

You are standing on the shore of a small lake and you see the opposite shore reflected in the lake's calm surface. You are trying to photograph the fish swimming in the lake, but the reflection of the shore makes it hard to see the fish. To eliminate most of that reflection, you should put a filter in front of the camera's lens that blocks

(A) short wavelength light. [0.0% picked]

(B) vertically polarized light. [6.2% picked]

(D) long wavelength light. [1.2% picked]

You are playing tug-o-war with a plastic clothesline. Your team and an opposing team are pulling at opposite ends of the cord and each team is trying to drag the other team into a mud puddle located between the two teams. After a few minutes without progress, your team suddenly pulls hard toward your side. The other team has anticipated this threat and is able to keep their end of the rope from moving. Your end of the rope stretches toward you and the rope breaks. Breaking the rope required energy and that energy was provided by

(A) the other team. [3.3% picked]

(B) both teams. [9.1% picked]

(D) neither team. It was instead provided by chemical potential energy in the rope itself. [0.8% picked]

Why are sodium oxide (soda) and calcium oxide (lime) added to silicon dioxide (silica) when making the glass used in most windows?

(A) Glass made from pure silica melts at too high a temperature to be practical in windows. [24.1% picked]

(B) Pure silica glass is not transparent. [15.8% picked]

(D) Pure silica cannot form a glass. [7.5% picked]

Answer: (A) Glass made from pure silica melts at too high a temperature to be practical in windows. [24.1% picked]

A television screen can make you see yellow by combining pure red light and pure green light. That combination of lights makes you see yellow because

(A) combining two of the primary colors of light produces the third primary color of light. [0.8% picked]

(B) the frequency of red light and the frequency of green light combine to produce the frequency of yellow light. [6.6% picked]

(D) the wavelength of red light and the wavelength of green light combine to produce the wavelength of yellow light. [17.0% picked]

Answer: (C) it stimulates the red- and green-sensing cells in your retina exactly as pure yellow light would. [73.9% picked]

If the speed of light in water did not depend on the wavelength of that light, a rainbow would

(A) appear white. [93.4% picked]

(B) still appear red on the outside and violet on the inside. [0.4% picked]

(D) appear reversed in color, with red on the inside and violet on the outside. [0.8% picked]

(A) the size of the real image on the image sensor increases so that the object appears closer. [8.3% picked]

(B) the depth of focus increases so that nearby and distant objects are in focus at once. [58.5% picked]

(D) the depth of focus decreases so that only the object you have focused on is in focus. [25.3% picked]

Answer: (B) the depth of focus increases so that nearby and distant objects are in focus at once. [58.5% picked]

The fallout from a nuclear explosion and the waste from a nuclear reactor contain radioactive isotopes. The atoms of these isotopes differ from stable atoms in that

(A) they are chemically unstable but their nuclei are indistinguishable from those of stable atoms. [11.6% picked]

(B) each atom emits a steady stream of X-ray radiation. [3.3% picked]

(D) their nuclei are unstable but they are chemically indistinguishable from stable atoms. [69.7% picked]

Answer: (D) their nuclei are unstable but they are chemically indistinguishable from stable atoms. [69.7% picked]

(A) neither electric nor magnetic fields. [0.4% picked]

(B) electric fields, but no magnetic fields. [5.4% picked]

(D) both electric and magnetic fields. [91.7% picked]

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

(A) its water content gives it more mass and that prevents it from absorbing energy. [0.8% picked]

(B) it stops the downward motion of your foot faster and thus absorbs less of your momentum. [14.9% picked]

(D) it pushes up on your foot just as hard as your foot pushes on it, unlike the soft dry sand. [8.7% picked]

Answer: (C) it doesn't move downward as you push downward on it, so you do almost zero work on it. [75.1% picked]

Separating the uranium-235 atoms from the uranium-238 atoms in natural uranium is extremely difficult because both uranium isotopes have the same

(A) number of protons. [69.7% picked]

(B) weight. [0.4% picked]

(D) mass. [6.2% picked]

At room temperature, polystyrene is a glassy plastic and cups made of polystyrene foam (e.g., Styrofoam) are rigid and brittle. But just above the temperature of boiling water, polystyrene begins to soften and it becomes leathery or even elastic in character. What happens in the polystyrene to make it less rigid at these high temperatures?

(A) Portions of the molecular chains begin to move relative to one another. [36.9% picked]

(B) Chemical bonds in the molecular chains break to form smaller chains. [24.5% picked]

(D) Crystals of polystyrene melt and the individual styrene molecules begin to flow from place to place. [21.2% picked]

Answer: (A) Portions of the molecular chains begin to move relative to one another. [36.9% picked]

A large sugar crystal is almost perfectly clear. If you crush that crystal, it becomes white because

(A) each surface in the crushed sugar partially reflects light. [77.6% picked]

(B) light passing through it travels at the same speed, regardless of wavelength. [5.0% picked]

(D) light passing through it experiences total internal reflection. [11.2% picked]

Answer: (A) each surface in the crushed sugar partially reflects light. [77.6% picked]

You are pulling a toy wagon up a steep hill and the wagon is traveling in a straight line at a steady pace. The net force that the wagon is experiencing

(A) points straight up. [9.1% picked]

(B) points uphill. [6.2% picked]

(D) points straight down. [7.9% picked]

If you hit an iron sheet with a hardened steel hammer, the iron sheet will dent but the hammer will not dent. Both objects are almost pure iron, so why does only the iron sheet dent?

(A) The small crystals of iron atoms in the iron sheet can move easily past one another, while the large crystals of iron atoms in the hardened hammer resist that motion. [10.8% picked]

(B) The iron atoms in the hammer are crystallized and therefore cannot move, while the iron atoms in the iron sheet are not crystallized and can easily shift from one place to another. [12.9% picked]

(C) The large crystals of iron atoms in the iron sheet can move easily past one another, while the small crystals of iron atoms in the hardened hammer resist that motion. [11.6% picked]

(D) The uniform layers of iron atoms in the iron sheet can slip across one another, while the distorted layers of iron atoms in the hardened hammer resist slipping. [60.2% picked]

Answer: (D) The uniform layers of iron atoms in the iron sheet can slip across one another, while the distorted layers of iron atoms in the hardened hammer resist slipping. [60.2% picked]

Tempering glass makes it very resistant to breakage. After it has been tempered, the surface of glass is

(A) highly compressed so that it is very difficult to tear. [71.8% picked]

(B) under great tension so that it is very difficult to stretch any further. [17.8% picked]

(D) much harder than normal glass so that only a diamond can scratch it. [7.1% picked]

Answer: (A) highly compressed so that it is very difficult to tear. [71.8% picked]