Given Saturday, May 6, 1995, from 9:00 AM to 12:00 Noon
PART I: MULTIPLE CHOICE QUESTIONS
Please mark the correct answer for each question on the bubble sheet. Fill in the dot completely with #2 pencil. Part I is worth 67% of the grade on this examination.
Problem 1:
The colors that you see when sunlight strikes a cut crystal wineglass or a cut diamond are a result of the fact that two light waves with
(A) the same wavelength in air can have different frequencies in a material.
(B) the same wavelengths can have different colors.
(C) the same frequency in air can have different wavelengths in a material.
(D) different wavelengths travel at different speeds in most materials.
Problem 2:
When you put on polarizing sunglasses, you are preventing horizontally polarized light from reaching your eyes. By "horizontally polarized," we mean that the light has its
(A) electric field oriented horizontally.
(B) magnetic field oriented horizontally.
(C) north and south magnetic poles separated horizontally.
(D) positive and negative electric charges separated horizontally
Problem 3:
Water and oil form separate layers in unshaken salad dressing because they do not dissolve in one another. Oil doesn't dissolve in water because
(A) both oil molecules and water molecules are positively charged and repel one another.
(B) water molecules are horizontally polarized while oil molecules are vertically polarized.
(C) the polar water molecules bind much more strongly to one another than to nonpolar oil molecules.
(D) oil is a liquid and liquids don't dissolve in liquids.
Problem 4:
If you were to build a motor using only permanent magnets, its rotor might spin briefly but it would soon come to a stop as friction turned its energy into heat. To keep the rotor turning, you must replace one of the magnets with an electromagnet and control that electromagnet so that it always does work on the rotor, increasing its energy. To do work on the rotor, the electromagnet should be adjusted so that it always
(A) repels each magnet that moves toward it and repels each magnet that moves away from it.
(B) repels each magnet that moves toward it and attracts each magnet that moves away from it.
(C) attracts each magnet that moves toward it and repels each magnet that moves away from it.
(D) attracts each magnet that moves toward it and attracts each magnet that moves away from it.
Problem 5:
If you put a heavy, 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) the magnetron will burn out and the microwave will stop working altogether.
(B) sparks will leap out of the marble and may burn the nearby broccoli.
(C) the marble will become red hot and the broccoli will remain raw.
(D) almost nothing will have happened to the marble and the broccoli will be partly cooked.
Problem 6:
The blades of a fan do work on the air in blowing it across the room. An electric motor keeps those fan blades turning. If you remove the fan blades from the motor, the motor will continue to turn at essentially the same rate but
(A) consume more electrical power.
(B) in the reverse direction.
(C) consume the same amount of electrical power.
(D) consume less electrical power.
Problem 7:
When you use a telephoto lens to take a picture of a distant object, that object appears larger in the final print than it would with a normal lens. The difference between a telephoto lens and a normal lens is that the telephoto lens has a
(A) smaller aperture than the normal lens.
(B) longer focal length than the normal lens.
(C) shorter focal length than the normal lens.
(D) larger aperture than the normal lens.
Problem 8:
Red light has a longer wavelength than blue light, so you know that, in empty space,
(A) red light travels faster than blue light.
(B) blue light has a higher frequency than red light.
(C) blue light travels faster than red light.
(D) red light has a higher frequency than blue light.
Problem 9:
If you hold a strong permanent magnet inside a metal ring and then quickly remove that magnet, you create an electric field in the metal ring and an electrical current flows through the metal ring. If you repeat this procedure with a glass ring, no current flows in the glass ring because
(A) the glass ring is made of a non-magnetic material. No magnetic fields can be present inside the ring so removing the magnet has no effect on the ring.
(B) although removing the magnet creates an electric field in the glass ring, the glass ring has no mobile electric charges to carry an electrical current.
(C) the glass ring creates its own magnetic field in the opposite direction, opposing the field of the permanent magnet and preventing any current flow.
(D) removing the magnet from the glass ring does not create an electric field.
Problem 10:
Many mail order catalogs sell lamp dimmer disks. These disks, which you insert in the sockets of incandescent lamps, promise to reduce your electrical bills while making the light bulbs last virtually forever. Unfortunately, these disks simply reduce the power delivered to the bulbs' filaments so that they operate below their rated temperature and waste energy producing infrared light. The dimmer disk actually contains a single diode that forms a series circuit with the light bulb. AC current from the power line must flow through the diode and then through the filament (or vice versa). Overall, this diode reduces the power delivered to the filament by about a factor of two because
(A) the diode halves the voltage of the current passing through the light bulb so that the power it receives is also halved.
(B) the diode behaves like a filament so that there are two filaments in a series, with each of them receiving half the power that a single filament would receive.
(C) the diode only allows current to flow in one direction so that during one half of each cycle of the AC power line, no current flows through the light bulb.
(D) the diode divides the current in half and only allows one half of that current to flow through the filament.
Problem 11:
When an electron with a great deal of kinetic energy passes very near the massive nucleus of a large atom, the electron's direction suddenly changes. The electron emits an X-ray because
(A) the passing electron causes a current to flow in the nucleus, releasing the electromagnetic wave.
(B) an accelerating electric charge emits an electromagnetic wave and this very abrupt acceleration produces a very high frequency wave.
(C) sliding friction causes its temperature to increase and it begins to glow white hot. It becomes so hot that it emits X-rays.
(D) a moving electric charge emits a visible electromagnetic wave but this wave becomes an X-ray when it is emitted near an atomic nucleus.
Problem 12:
When you leave a xerographic copy pressed tightly against a vinyl notebook or chair, the plasticizers in the vinyl diffuse into the plastic toner on the xerographic copy. The result is that the toner
(A) changes from the rubbery flow regime to the glassy regime and breaks away from the paper and onto the vinyl surface.
(B) becomes a vulcanized thermoset and melts onto the vinyl surface.
(C) becomes electrically charged again and is attracted to the oppositely charge vinyl surface.
(D) changes from the glass-rubber transition regime to the rubbery flow regime and sticks to the vinyl surface.
Problem 13:
You place a bowl of soup on a ceramic saucer and put the two into a microwave. After a minute or two of cooking, the soup is very hot but the saucer is still cold because
(A) the saucer contains no water molecules and doesn't absorb microwaves.
(B) the oven's microwaves are directed downward from above and are absorbed by the soup before they can reach the saucer.
(C) the saucer is horizontal and the microwaves are horizontally polarized. A horizontal object can't absorb horizontally polarized electromagnetic waves.
(D) the saucer is horizontal and the microwaves are vertically polarized. A horizontal object can't absorb vertically polarized electromagnetic waves.
Problem 14:
Adding sodium oxide (soda) to quartz produces a softer glass that melts at a lower temperature than pure quartz. Soda has this effect because
(A) it carbonates the glass and reduces its potential energy.
(B) it darkens the glass so that it absorbs thermal radiation better and melts more easily.
(C) it adds thermal energy to the quartz so that the quartz behaves as though it were hotter.
(D) it terminates the network of covalent bonds in the quartz, weakening that network.
Problem 15:
Two people are loading suitcases into a truck. The suitcases have equal weights and roll easily on wheels. The man pushes a suitcase up a 2 meter ramp with a force of 100 newtons while the woman pushes a suitcase up a 4 meter ramp with a force of 50 newtons. Which person is doing the most work?
(A) The woman is doing more work because she is pushing the suitcase a longer distance while raising the suitcase to the height of the truck.
(B) They are both doing zero work on their suitcases because the suitcases roll freely on wheels.
(C) They are both doing the same amount of work because the product of force times distance is the same in each case.
(D) The man is doing more work because he is raising the suitcase to the height of the truck with a larger force.
Problem 16:
You get on your bicycle and begin pedaling. You travel forward faster and faster and soon reach full speed. As you are picking up speed, friction between the ground and the bicycle wheels is exerting
(A) a forward force on the bicycle.
(B) zero force on the bicycle.
(C) a backward force on the bicycle.
(D) an upward force on the bicycle.
Problem 17:
Celluloid plastic has a serious drawback:
(A) it doesn't dissolve in anything.
(B) it burns very easily.
(C) it is opaque.
(D) it melts at room temperature.
Problem 18:
Tempering glass makes it very resistant to breakage. After it has been tempered, the surface of glass is
(A) much smoother than normal glass so that sharp objects just slide off of it.
(B) under great tension so that it is very difficult to stretch any further.
(C) much harder than normal glass so that only a diamond can scratch it.
(D) highly compressed so that it is very difficult to tear.
Problem 19:
Fluorescent brighteners are added to laundry detergents to increase the amount of blue light emitted by aging, yellowed fabrics. Brighteners obtain the energy they need to emit this additional blue light from
(A) ultraviolet light.
(B) radio waves and microwaves.
(C) infrared light.
(D) red light.
Problem 20:
A photoconductor can't carry an electrical current in the dark because all of its valence levels contain two electrons and moving a valence-level electron into one of the empty conduction levels requires too much energy. While the photoconductor would be able to carry current if its electrons could move from one valence level to another, such movement is impossible because
(A) the velocity of an electron in the photoconductor is conserved and can't change.
(B) the momentum of an electron in the photoconductor is conserved and can't change.
(C) the laws of motion prevent electrons from changing valence levels.
(D) no more than two electrons can be in each valence level; one spin-up and one spin-down.
Problem 21:
X-rays create an image of bone on a sheet of photographic film because
(A) the hydrogen atoms in tissue absorb X-rays much more effectively than do the heavier atoms in bone. The tissue casts dark shadows on the film.
(B) X-rays are conducted much more effectively through bone than through tissue. They strike the photographic film, which then fluoresces white wherever bone is present.
(C) the calcium atoms in bone absorb X-rays much more effectively than the lighter atoms in tissue. The bones cast shadows on the film.
(D) X-rays are reflected by metals such as the calcium in bone. X-rays reflected from the bones are imaged with a lens to form a real image of the bones on photographic film.
Problem 22:
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 stable atoms.
(B) their nuclei are unstable but they are chemically indistinguishable from stable atoms.
(C) each atom emits a steady stream of X-ray radiation.
(D) their nuclei are unstable and they are chemical unstable.
Problem 23:
A typical lawnmower has an electromagnetic device called a magneto that produces a brief pulse of very high voltage electric charge. This charge runs through a short wire to the spark plug, where it jumps across a gap to produce the spark that ignites the gasoline. Unfortunately, the lawnmower interferes with the reception on your portable radio because
(A) the presence of electric charge in the magneto prevents current from flowing up and down your portable radio's antenna.
(B) when the charge accelerates during each ignition pulse, it emits radio waves.
(C) the alternating current used in the lawnmower's ignition system is incompatible with your portable radio, which requires direct current for its operation.
(D) the magnetic field from the magneto attracts charge out of your radio's antenna so that it becomes electrically neutral.
Problem 24:
Laser light is unusual because
(A) it consists of a great many identical photons.
(B) it has a much higher frequency than normal visible light.
(C) it has a much shorter wavelength than normal visible light.
(D) it is much brighter than normal visible light.
Problem 25:
To make you see the color yellow, a color television illuminates its
(A) red and blue phosphors simultaneously.
(B) yellow phosphors.
(C) blue and green phosphors simultaneously.
(D) red and green phosphors simultaneously.
Problem 26:
Exposure to sunlight creates a small quantity of three-atom oxygen molecules, a chemical called "ozone." These ozone molecules absorb short-wavelength ultraviolet light and reduce the amount of that light striking the earth's surface. The presence of the ozone is a good thing for us because short-wavelength ultraviolet light
(A) heats our skins quickly, causing thermal damage and burns.
(B) causes damage to the atomic nuclei in our skins.
(C) is absorbed in packets with enough energy to do chemical damage to molecules in your skin.
(D) exerts strong forces on electric charges in our skin, cause large and damaging currents to flow through us.
Problem 27:
Egg whites are essentially clear. However, when you beat air bubbles into egg whites while making meringues or a soufflé, the mixture becomes white because
(A) stretched egg whites absorb black light, leaving only white light to be reflected.
(B) some light is reflected whenever light moves from a layer of egg white to a layer of air or vice versa.
(C) stretched egg whites are less dense than normal egg whites and fluoresce white light when exposed to infrared radiation.
(D) stretched egg whites are more dense than normal egg whites and fluoresce white light when exposed to infrared radiation.
Problem 28:
A nuclear power plant does work when it generates electrical power. The energy use to do this work entered the power plant as
(A) electrostatic potential energy in the repelling protons of uranium-235 nuclei.
(B) nuclear potential energy in the attracting neutrons of uranium-235 nuclei.
(C) nuclear potential energy in the attracting neutrons and protons of uranium-235 nuclei.
(D) nuclear potential energy in the repelling neutrons of uranium-235 nuclei.
Problem 29:
When you look at yourself in a makeup mirror, you see an enlarged virtual image of yourself. The image that you see appears to be located
(A) on the surface of the mirror.
(B) behind the mirror, where you can't touch it.
(C) just in front of the mirror, where you can touch it.
(D) just in front of your eye, where it appears extremely large.
Problem 30:
Any rotating object that is experiencing zero torque will
(A) gradually increase its rate of rotation.
(B) gradually slow its rotation until it begins to reverse directions.
(C) continue rotating with constant angular momentum.
(D) gradually slow its rotation until it comes to a complete stop.
Problem 31:
You have a pair of fabulous stereo speaker cabinets. Each cabinet contains 5 individual speakers. Unfortunately, one of the individual speakers is broken, so you buy an identical replacement and install it yourself. In the process, you reverse the two electrical connections to the speaker so that current flows backward through the speaker coil. The speaker cone moves the wrong way and makes the entire stereo sound odd. The speaker cone moves the wrong way because
(A) the charge on the speaker coil becomes positive rather than negative so that it is pushed in the wrong direction by the speaker's permanent magnet.
(B) the current flowing backward through the speaker coil magnetizes it backward so that it is pushed in the wrong direction by the speaker's permanent magnet.
(C) the current flowing backward through the speaker coil polarizes its electrical charges backward so that they are attracted when they should be repelled and repelled when they should be attracted.
(D) the charge on the speaker coil becomes negative rather than positive so that it is pushed in the wrong direction by the speaker's permanent magnet.
Problem 32:
The microscope structure of quartz glass (amorphous quartz) closely resembles that of
(A) gelatin (unflavored and unsweetened).
(B) steel.
(C) molten quartz (liquid quartz).
(D) crystalline quartz (quartz crystals or quartz sand).
Problem 33:
Unlike an incandescent light bulb, which can be connected directly to the power line, a fluorescent tube requires some additional equipment because
(A) although the discharge starts without help, a ballast is needed to limit the current through the discharge once it starts.
(B) its electrodes must be heated to start the discharge and a ballast is needed to limit the current through the discharge once it starts.
(C) although the discharge operates without help once it starts, its electrodes must be heated to start the discharge.
(D) there is no filament connecting the two ends of the fluorescent tube so no current can flow through the tube.
Problem 34:
A novel way to freeze ice cream is to mix its ingredients with ultracold liquid nitrogen. The mixture freezes so quickly that the ice crystals that form are all very tiny and the resulting ice cream is very smooth. If you could freeze the ingredients even faster, so that they did not have time to form any crystals at all before their molecules ceased their thermal motions, the ice cream would
(A) be a polymer.
(B) be a gel.
(C) be a thermoset plastic.
(D) be a glass.
Problem 35:
You are moving two files cabinets. One cabinet is empty and is resting directly on the floor. The other cabinet is full of documents but is resting on a dolly with wheels. You push each cabinet forward 5 meters by exerting a forward force of 100 newtons on it. At the end of this pushing,
(A) the rolling cabinet has about 500 joules of kinetic energy while the sliding cabinet has much less than 500 joules of kinetic energy.
(B) the rolling cabinet and the sliding cabinet each have much less than 500 joules of kinetic energy.
(C) the rolling cabinet and the sliding cabinet each have about 500 joules of kinetic energy.
(D) the sliding cabinet has about 500 joules of kinetic energy while the rolling cabinet has much less than 500 joules of kinetic energy.
Problem 36:
The beam of electrons in a television picture tube is deflected horizontally and vertically by
(A) electric fields produced by electric charges placed on the inside of the picture tube's front surface.
(B) magnetic fields produced by an array of small permanent magnets mounted on the inside surface of the neck of the picture tube.
(C) electromagnetic waves produced by a magnetron attached to the back wall of the picture tube.
(D) magnetic fields produced by currents flowing through wire coils on the neck of the picture tube.
Problem 37:
Which of the following creates a magnetic field?
(A) Only a constant electric field.
(B) Only an electric field that changes with time.
(C) Only a moving electric charge.
(D) Both a moving electric charge and an electric field that changes with time.
Problem 38:
When you see colors reflected from the face of a soap bubble, you are seeing what happens when
(A) light refracts as it passes through the thin, uniform layer of soapy water on the outside of the bubble.
(B) light reflects from the individual colored soap molecules in the bubble.
(C) a light wave follows two paths to your eye and the two halves of that wave interfere with one another.
(D) light is bent as it passes through the bubble, as though through a ball of glass or a glass lens.
Problem 39:
When you reduce the aperture of the lens in your camera,
(A) the size of the real image on the film increases so that the object appears closer.
(B) the depth of focus decreases so that only the object you have focused on is in focus.
(C) the size of the real image on the film decreases so that the object appears more distant.
(D) the depth of focus increases so that nearby and distant objects are in focus at once.
Problem 40:
A thermal 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) heat the uranium up so that the uranium-238 turns into a gas and does not interact with fission neutrons.
(B) make hydrogen, which then experiences fusion to form helium.
(C) slow the fission neutrons down so that they interact only with uranium-235.
(D) heat the uranium up so that it undergoes fission more easily.
Problem 41:
In a transformer, a changing current in the primary circuit induces a changing current in the secondary circuit. More specifically, the energy of an electric charge in the transformer's secondary coil increases as it travels through the secondary coil. This additional energy comes from work done on that charge by
(A) microwaves emitted by the transformer's primary coil; conveying energy from the primary circuit to the secondary circuit.
(B) an electric field created by the changing magnetic field of the transformer.
(C) the transformer's capacitor, which stores electrostatic potential energy.
(D) a magnetic field created by the changing electric field of the transformer.
Problem 42:
Magnetic resonance imaging uses radio waves and a strong magnetic field to locate
(A) hydrogen nuclei (protons) within the body of the person being studied.
(B) covalent bonds within the body of the person being studied.
(C) electrons within the body of the person being studied.
(D) calcium atoms (bones) within the body of the person being studied.
Problem 43:
In air, the laser beam used in a CD player has a frequency of about 380,000,000,000,000 Hz and a wavelength of about 780 nanometers. In the plastic CD disk, that same beam has
(A) a shorter wavelength and a higher frequency.
(B) a shorter wavelength but the same frequency.
(C) a longer wavelength and a higher frequency.
(D) a longer wavelength and a lower frequency.
Problem 44:
A skydiver leaps out of an airplane and begins to fall. After a few seconds, he reaches a constant downward speed of about 300 kilometers-per-hour (190 miles-per-hour). The net force he is experiencing at that point is
(A) downward, because the only force acting on him is gravity. He is in free fall.
(B) upward, because he is in free fall and the only force he experiences is an upward centrifugal force.
(C) downward, because his velocity is downward and net force is proportional to velocity.
(D) zero, because the upward drag force exerted on him by the air is equal to his weight.
Problem 45:
Which of the following electronic devices allows a very small electrical signal to control a large electrical current?
(A) A capacitor.
(B) A diode.
(C) A resistor.
(D) A transistor.
Problem 46:
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 remains
(A) considerably less than 10 meters above the ground.
(B) considerably more than 10 meters above the ground.
(C) just a little less than 10 meters above the ground.
(D) 10 meters above the ground.
Problem 47:
The tank circuit in a radio transmitter helps the transmitter to
(A) move electrical current more quickly through its resistor.
(B) store more electric charge in its battery.
(C) collect the electric charge that accumulates at the top of the antenna and return it to the bottom of the antenna, where it can be reused.
(D) move more electric charge up and down the antenna.
Problem 48:
The sky is blue because
(A) most polluting gases and dust particles in the air are bluish in color and lend their color to that of the sky.
(B) tiny particles in the air are more efficient at scattering short wavelength light than they are at scattering long wavelength light.
(C) air molecules absorb red light more efficiently than they do blue light because of their electron orbitals.
(D) air molecules absorb blue light more efficiently than they do red light because of their electron orbitals.
Problem 49:
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) light encountering a surface produces mobile electrons in that surface that make it metallic. The metalized surface then reflects the light perfectly.
(B) the speed of light in the material drops to exactly 1/2 its value in air and the light reflects from it perfectly.
(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.
(D) the refractive index of the glass becomes infinite and light reflects from it perfectly.
Problem 50:
A battery
(A) creates positive charge.
(B) pumps positive charge from its positive terminal to its negative terminal.
(C) pumps positive charge from its negative terminal to its positive terminal.
(D) creates negative charge.
PART II: SHORT ANSWER QUESTIONS
Please give a brief answer in the space provided. Part II is worth 33% of the grade on this examination.
Problem 1:
You have just stepped out of a drenching spring rainstorm. You plug your hairdryer into the upper socket of a 120 volt electrical outlet and begin to dry your hair. The hairdryer carries a current of 10 amperes, weighs 10 newtons, and produces air with a temperature of 70° C.
(A) How could you calculate how much electrical power the hairdryer
is using (you don't have to do this calculation; just describe
how to calculate it)?
(B) Like most electrical conductors, the heating coil in the hairdryer
obeys Ohm's law. When a downed tree breaks a nearby power line,
the voltage at your electrical outlet drops to 110 volts for a
second or two. What effect does this change in voltage have on
the current passing through your hairdryer?
(C) Your roommate also has wet hair. When the second, identical
hairdryer is plugged into the lower socket of the same electrical
outlet, the two hairdryers are in a parallel circuit. Neglecting
power losses in the electrical wires themselves, how does the
presence of this second hairdryer affect (1) the voltage drop
across your hairdryer and (2) the current passing through it?
(D) How does the presence of the second hairdryer affect the total
current flowing through the electrical outlet from the power company?
Problem 2:
Super-Duper-Man has muscles of brass, is faster than a speeding Frisbee, and can leap over a double-wide mobile home in a single bound. As we join our hero, we find him standing on the bathroom scale after a large breakfast at the Tavern.
(A) The scale reads about 1000 newtons. What is Super-Duper-Man's
mass? (Note: water's density is 1000 kg per cubic meter, atmospheric
pressure is about 100,000 newtons per square meter, the acceleration
due to gravity is 9.8 N/kg, Newton's second law is force equals
mass times acceleration, and one dollar is roughly equal to 85
yen and falling.)
(B) His bedraggled appearance notwithstanding, Super-Duper-Man
is truly impervious to injury. As soon as he steps out of his
apartment door, his arch nemesis T-Barney (cousin of T-Rex) fires
a cannonball at Super-Duper-Man but it bounces harmlessly off
his chest. Although he is not injured, Super-Duper-Man does obey
the laws of physics. What happens to Super-Duper-Man's velocity
as a consequence of this attack?
(C) Super-Duper-Man then begins to exert a huge stress on T-Barney's
cannon. At first the cannon deforms elastically, returning to
its original shape whenever Super-Duper-Man lets go. However,
after one mighty shove, the barrel of the cannon deforms permanently
and the world is a safer place. What happened to the microscopic
structure of the cannon when it finally bent permanently?
(D) Unrepentant, T-Barney then pushes Super-Duper-Man's friend
and colleague Lowest Lien off of tall building. Super-Duper-Man
rushes to her aid. He reaches out his arms for a diving catch,
a foot above the ground. What happens to Lowest Lien and why?
Problem 3:
You are very proud of your new 12,000 square-foot house. However, you are not just the occupant; you are also the gardener. Unfortunately, you are now so deeply in debt that you can only afford to buy a cheap, used rotary lawnmower. Your choices are a walk-behind mower or a riding mower. You look at the 12 acres of grass surrounding your mansion and go for the riding mower. The only problem: its blade is missing. Since you have access to a big pile of scrap metal, you decide to make a blade yourself. A blade for this type of mower is little more than a sharpened metal bar that spins very rapidly about a central pivot.
(A) Your first choice in the scrap heap is a bar of chemically
pure iron. You fashion a nice blade from this metal but find that
it cannot keep an edge. What is going on inside of the pure iron
that allows it to become dull so easily?
(B) Your next choice is a bar of stainless steel. You are helped
in identifying it as stainless steel because a magnet does not
stick to it. Why doesn't the magnet stick to the stainless steel?
(C) The stainless steel blade can't keep an edge either, so you
finally try a bar of carbon steel. After shaping the blade, you
heat its cutting edge in burning charcoal so that it soaks up
extra carbon. You then cool the blade very rapidly in water. The
result is a fine blade that stays sharp almost indefinitely. Why
did adding carbon to the cutting edge and then cooling the red
hot edge quickly make it so resistant to dulling?
(D) Your mower cuts the grass beautifully. As the spinning blade
slices through a tall weed, the weed hardly moves at all. What
keeps the weed in place while it is being cut by the moving blade?
Problem 4:
The inexpensive disposable cameras that are sold in grocery stores contain quite a number of technologically interesting components. Despite their apparent simplicity, these cameras are carefully designed, manufactured, and assembled.
(A) While more sophisticated cameras require careful focusing
to form sharp images on film, disposable cameras don't need focusing.
What characteristic of a disposable camera accounts for its huge
depth of focus?
(B) The camera lens is normally made from a clear plastic with
a refractive index of 1.55. If someone accidentally made the lens
from a clear plastic with a refractive index of 1.45, the photographs
would be blurry. Does the lens still form a real image and, if
so, where is it located?
(C) The camera lens is normally made from a plastic with very
little dispersion. If someone accidentally made the lens from
a plastic with a lot of dispersion, each bright point of light
in the original scene would appear with rainbows of color around
it in the photograph. Why?
(D) The camera's electronic flash uses a clear tube containing
the rare and expensive gaseous element xenon. If someone accidentally
put the less expensive gaseous element neon in the tube, the flash
would emit reddish light. What characteristic of neon gas causes
it to emit reddish light?
Problem 5:
You are working as a summer intern at a company that manufactures kitchen appliances. You have been assigned to a team developing a new small-capacity food processor.
(A) The food processor will operate from the power line. Because
of its small capacity, it needs very little power and one of the
designer's suggests using only one half of the power outlet. The
power cord would have only a single prong at the end. Would this
scheme work? Explain briefly why or why not.
(B) The processor's rotating knife blade will turn very quickly
and will slice up food placed loosely in its container. Why won't
the food move out of the blade's way?
(C) The processor's motor must turn the blades very rapidly. One
of the designers suggests using a DC motor, with a wire coil that
rotates in an arrangement of stationary permanent magnets. You
point out that the motor will not work properly on the AC current
from the power line. Why not?
(D) A technician finds that when the completed processor is operated
near a color television that the television image is badly distorted.
Explain.
Problem 6:
Impressed by your mastery of video games, the local nuclear power plant has offered you a part-time job controlling their reactor. The graphics are lousy and the controls aren't very responsive, but the pay is good so you take the job.
(A) You are supposed to move the control rods up and down to maintain
a steady rate of nuclear decays in the reactor core. You find
that when you insert the control rods too far into the core, the
rate of nuclear decays diminishes. Since natural radioactive decay
is completely random and cannot be controlled by outside influences,
how do the control rods affect the rate at which uranium-235 nuclei
decay in a reactor?
(B) Water flows through the reactor core at an enormous rate.
Why must the water keep moving?
(C) The power plant produces electricity for weeks without needing
any fuel shipments and without releasing anything into the environment.
What is being consumed to produce this electrical energy?
(D) After four weeks, you become so bored with work that you decide
to see what will happen when you pull the control rods completely
out of the reactor core. The sound and light effects that follow
are totally awesome but you don't get a replay. What has probably
happened to the reactor core?