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:
At present, a compact disc can only hold about 1 hour of music. This limit is due to the fact that
(A) light can't be focused to a spot that is significantly smaller than its wavelength.
(B) a compact disc can't turn faster than about 5 turns per second without experiencing a net torque of zero.
(C) a compact disc can't turn slower than about 5 turns per second without experiencing a net torque of zero.
(D) the ridges in the aluminum layer of the compact disc can't experience destructive interference unless they have a wavelength that is almost equal to distance between them.
Problem 2:
You drop your boom box and one of the two wires that connects the batteries to the electronics is severed. While you might hope that the device would continue working at half its normal volume, you find that it doesn't work at all. That's because both wires are necessary for the boom box to operate. One wire carries
(A) electric fields to the electronics and the other wire carries magnetic fields to the electronics.
(B) current to the amplifier while the other wire carries current to the speakers.
(C) electric current to the electronics while the other wire carries magnetic poles to the speakers.
(D) current to the electronics and the other wire returns that current to the batteries.
Problem 3:
A skydiver leaps out of an airplane and begins to fall. After a few seconds, she reaches a constant downward speed of about 300 kilometers-per-hour (190 miles-per-hour). The net force she is experiencing at that point is
(A) downward, because her velocity is downward and net force is proportional to velocity.
(B) downward, because the only force acting on her is gravity. She is in free fall.
(C) upward, because she is in free fall and the only force she experiences is an upward centrifugal force.
(D) zero, because the upward drag force exerted on her by the air is equal to her weight.
Problem 4:
Two steel balls, one of which weighs twice as much as the other, roll off of a horizontal table with the same speeds. In this situation,
(A) the lighter ball hits the floor at about half the horizontal distance from the base of the table than does the heavier ball.
(B) both balls hit the floor at approximately the same horizontal distance from the base of the table.
(C) the heavier ball hits the floor at about half the horizontal distance from the base of the table than does the lighter ball.
(D) the heavier ball hits considerably closer to the base of the table than the lighter ball, but not necessarily half the horizontal distance.
Problem 5:
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) heat the uranium up so that it undergoes fission more easily.
(C) make hydrogen, which then experiences fusion to form helium.
(D) slow the fission neutrons down so that they interact only with uranium-235 nuclei.
Problem 6:
The microscope structure of quartz glass (amorphous quartz) closely resembles that of
(A) crystalline quartz (quartz crystals or quartz sand).
(B) gelatin (unflavored and unsweetened).
(C) molten quartz (liquid quartz).
(D) steel.
Problem 7:
Magnetic resonance imaging uses radio waves and a strong magnetic field to locate
(A) calcium atoms (bones) within the body of the person being studied.
(B) electrons within the body of the person being studied.
(C) hydrogen nuclei (protons) within the body of the person being studied.
(D) covalent bonds within the body of the person being studied.
Problem 8:
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) their nuclei are unstable and they are chemical unstable.
(B) they are chemically unstable but their nuclei are indistinguishable from stable atoms.
(C) their nuclei are unstable but they are chemically indistinguishable from stable atoms.
(D) each atom emits a steady stream of X-ray radiation.
Problem 9:
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) different wavelengths travel at different speeds in most materials.
(D) the same frequency in air can have different wavelengths in a material.
Problem 10:
Which of the following creates a magnetic field?
(A) Only a moving electric charge.
(B) Only a constant electric field.
(C) Only an electric field that changes with time.
(D) Both a moving electric charge and an electric field that changes with time.
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) sliding friction causes its temperature to increase and it begins to glow white hot. It becomes so hot that it emits X-rays.
(B) the passing electron causes a current to flow in the nucleus, releasing the electromagnetic wave.
(C) an accelerating electric charge emits an electromagnetic wave and this very abrupt acceleration produces a very high frequency wave.
(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 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) behind the mirror, where you can't touch it.
(B) just in front of the mirror, where you can touch it.
(C) just in front of your eye, where it appears extremely large.
(D) on the surface of the mirror.
Problem 13:
X-rays create an image of bone on a sheet of photographic film because
(A) 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.
(B) 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.
(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) 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.
Problem 14:
Collisions can induce fission in some large atomic nuclei. Neutrons can induce fission more easily than protons because
(A) neutrons and nuclei are oppositely charged and attract one another.
(B) neutrons and nuclei have like charges and repel one another intensely as they approach.
(C) neutrons aren't repelled as they approach nuclei.
(D) neutrons move more rapidly than protons and can reach the nuclei before the nuclei have time to move out of the way.
Problem 15:
Cutting a loaf of bread causes a gentle stress on a knife blade. The strain experienced by the blade as the result of this stress is
(A) zero unless the blade undergoes plastic deformation.
(B) proportional to the stress.
(C) constant and doesn't depend on the stress.
(D) zero unless the blade undergoes slip.
Problem 16:
A battery
(A) pumps positive charge from its negative terminal to its positive terminal.
(B) creates positive charge.
(C) creates negative charge.
(D) pumps positive charge from its positive terminal to its negative terminal.
Problem 17:
Three factory workers are loading office chairs into a truck. All the chairs are the same and they have wheels on their legs. They are located on the ground behind the truck. The first person lifts chairs straight up in order to load them into the truck. The second person rolls the chairs slowly up a very long, very gradual ramp to load them into the truck. The third person rolls the chairs slowly up a rather short, rather steep ramp to load them into the truck. Which person does the most work on each chair while transferring it from the ground to the back of the truck?
(A) The third person does the most work on each chair.
(B) The first person does the most work on each chair.
(C) The three people do the same amount of work on each chair.
(D) The second person does the most work on each chair.
Problem 18:
You are pushing a large box straight across the floor at a constant speed of 4.0 m/s. What can you conclude about the forces acting on the box?
(A) The amount of forward force you are exerting on the box must be more than its weight.
(B) The amount of forward force you are exerting on the box is equal to the amount of backward force that sliding friction is exerting on the box to resist its motion.
(C) If the forward force you are exerting on the box is doubled, the constant speed of the box will increase to 8.0 m/s.
(D) The amount of forward force you are exerting on the box must be more than the amount of backward force that sliding friction is exerting on the box to resist its motion.
Problem 19:
When a rubber ball dropped from rest bounces off the floor, its direction of motion is reversed because
(A) the floor is in the way and the ball has to keep moving.
(B) the momentum of the ball is conserved.
(C) the energy of the ball is conserved.
(D) the floor exerts a force on the ball that stops its fall and then drives it upward.
Problem 20:
When laser light reflects from a soap bubble, its photons can interfere with one another. In contrast, when sunlight reflects from a soap bubble, each photon can interfere only with itself. The reason for this difference is that
(A) the photons in a laser beam are both vertically and horizontally polarized, while those in sunlight are only vertically polarized.
(B) the photons in a laser beam have both electric and magnetic fields, while those in sunlight have only electric fields.
(C) the photons in a laser beam are all part of a single wave, while those in sunlight are independent waves.
(D) the photons in a laser beam have both electric and magnetic fields, while those in sunlight have only magnetic fields.
Problem 21:
You're doing an internship in a very small city with no nearby radio stations. You find a weak AM station that plays good music but the static you hear in the background is almost unbearable. This static is present because the radio wave from the distant AM station is weak by the time it reaches your AM receiver and because
(A) the radio wave from a distant station becomes horizontally polarized by the time it reaches your antenna and can't magnetize the antenna.
(B) that radio wave becomes electrically charged by the time it arrives at your receiver, causing a build up of charge on the receiver's antenna.
(C) the wavelength of the station's radio wave becomes so long by the time it reaches your receiver that the receiver's antenna can't respond to it.
(D) your receiver can't distinguish between that weak radio wave and similar waves from surrounding objects.
Problem 22:
The tubes in fluorescent lamps have a white powder on their inner surfaces. This powder
(A) scatters the white light produced by the gas atoms inside the tube so that it is both vertically and horizontally polarized and doesn't cause glare.
(B) conducts electricity from one electrode to the other and emits white light as current passes through it.
(C) slows down the white light produced by the gas atoms inside the tube so that less of that white light reflects as it passes through the walls of the tube.
(D) absorbs ultraviolet light and uses the energy from that light to produce white light.
Problem 23:
Changing the amplitude of an electromagnetic carrier wave to represent sound or video introduces sideband waves at
(A) frequencies above and below the carrier wave's frequency.
(B) frequencies below the carrier wave's frequency.
(C) frequencies above the carrier wave's frequency.
(D) the frequency of the carrier wave.
Problem 24:
Which of the following electronic devices allows a very small electric signal to control a large electric current?
(A) A transistor.
(B) A diode.
(C) A resistor.
(D) A capacitor.
Problem 25:
When you use a wide angle lens to take a picture of a group of friends, the people appear smaller in the final print than they would have with a normal lens. The difference between a wide angle lens and a normal lens is that the wide angle lens has a
(A) shorter focal length than the normal lens.
(B) longer focal length than the normal lens.
(C) smaller aperture than the normal lens.
(D) larger aperture than the normal lens.
Problem 26:
The large sugar crystals found in rock candy are essentially clear. However granulated sugar looks white because
(A) small sugar grains can absorb black light, leaving only white light to be reflected.
(B) small sugar grains are more dense than large sugar crystals, and they fluoresce white light when exposed to infrared radiation.
(C) some light is reflected whenever light moves from a sugar granule to air or vice versa.
(D) small sugar grains are metallic and act as mirrors, scattering light in all directions.
Problem 27:
You are rearranging your dorm room furniture. You push the bed forward and it slides across the level floor at a constant velocity. Despite the fact that you are pushing the bed forward hard, the bed's kinetic energy doesn't increase because
(A) you are not doing any work on it. To do work on the bed, its velocity must increase.
(B) the work you are doing on it is being converted into thermal energy by sliding friction.
(C) the work you are doing on it is being converted into gravitational potential energy by gravity.
(D) you are not doing any work on it. To do work on the bed, its mass must increase.
Problem 28:
One of the goals of materials science is to form metals that have no crystalline structure. Such amorphous metals would be hard and elastic. If you tried to dent such a metal with a hammer, you would find that it would
(A) only dent if you hit is very rapidly with a very hard hammer.
(B) not dent-it would only shatter.
(C) only dent if you hit it very slowly with a very massive hammer.
(D) only dent if you hit it very rapidly with a very massive hammer.
Problem 29:
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) highly compressed so that it is very difficult to tear.
(C) under great tension so that it is very difficult to stretch any further.
(D) much harder than normal glass so that only a diamond can scratch it.
Problem 30:
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) air molecules absorb red light more efficiently than they do blue light because of their electron orbitals.
(C) tiny particles in the air are more efficient at scattering short wavelength light than they are at scattering long wavelength light.
(D) air molecules absorb blue light more efficiently than they do red light because of their electron orbitals.
Problem 31:
Suppose that you have a capacitor in front of you, with a wire connecting its two plates. You remove the wire and begin to transfer positive charges from the left plate to the right plate, one charge every second. With each additional transfer, your job gets harder because the forces pushing the charge in the opposite direction get stronger and stronger. The increasing amount of work you must do on each charge as you transfer it is reflected in the
(A) increasing current passing through the capacitor.
(B) increasing net charge on the capacitor.
(C) increasing magnetic field inside the capacitor.
(D) increasing voltage rise across the capacitor.
Problem 32:
As the frequency of an electromagnetic wave increases, its wavelength
(A) becomes longer.
(B) stays the same.
(C) becomes equal to that of a microwave.
(D) becomes shorter.
Problem 33:
If you plug an electric hairdryer into the wall outlet and turn it on, current will begin to flow through wires inside the wall. Some of the electric power carried by that current will be wasted as heat in those wires. If you plug a second identical hairdryer into the same outlet and turn it on, the amount of current flowing through each wire in the wall will double. The amount of power wasted in the wires of wall will
(A) increase by a factor of 4.
(B) remain almost the same because the voltage in the wires will change very little.
(C) remain almost the same because the current in the wires will change very little.
(D) increase by a factor of 2.
Problem 34:
If you put an egg in a microwave oven, it will become very hot. But if you put a dehydrated egg (a dried egg containing no water) in the microwave oven, the egg won't be affected because
(A) the dehydrated egg is too dry to have a temperature. Only foods containing water or oil can actually become hot.
(B) the dehydrated egg is much less dense than a normal egg and doesn't conduct heat well.
(C) the dehydrated egg reflects the microwaves while the normal egg does not.
(D) microwaves transfer heat to food principally through its water molecules.
Problem 35:
When you bring the pole of a permanent magnet close to a piece of aluminum, the aluminum repels it briefly. However, this repulsion disappears after a second or two because
(A) the magnetic domains in the aluminum flip so that they begin to attract the permanent magnet.
(B) the magnetic domains in the aluminum return to pointing in random directions.
(C) the electric current that makes the aluminum magnetic loses energy and comes to a stop.
(D) the magnetization of the aluminum reverses directions 120 times per second, so that there is no average attraction or repulsion.
Problem 36:
The energy that's released from uranium in a nuclear reactor was put into the uranium by a star that exploded more than 4.5 billion years ago. During the explosion, the star brought together two or more small nuclei to form each uranium nucleus. Combining these nuclei took energy because
(A) the smaller nuclei repelled one another as they were brought together.
(B) the smaller nuclei attracted one another as they were brought together.
(C) the nuclear force is only present in small nuclei and not in large nuclei such as uranium.
(D) the nuclear force requires an enormous amount of energy to activate.
Problem 37:
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 oven's microwaves are directed downward from above and are absorbed by the soup before they can reach the saucer.
(B) the saucer is horizontal and the microwaves are vertically polarized. A horizontal object can't absorb vertically polarized electromagnetic waves.
(C) the saucer contains no water molecules and doesn't absorb microwaves.
(D) the saucer is horizontal and the microwaves are horizontally polarized. A horizontal object can't absorb horizontally polarized electromagnetic waves.
Problem 38:
A rubber tire can't melt because
(A) its crystals are unable to undergo slip and don't exhibit plastic deformation.
(B) it is already a liquid crystal polymer, like Kevlar or Spectra.
(C) it has no crystalline structure and materials that aren't crystalline can't melt.
(D) its molecular chains are cross-linked, making it one giant molecule.
Problem 39:
A boy throws a steel ball straight up. Disregarding any effects of air resistance, the force(s) acting on the ball while it's above the ground is (are)
(A) a constant downward force of gravity and an upward force that steadily decreases until the ball reaches its highest point, after which there is only the constant downward force of gravity.
(B) a steadily decreasing upward force while the ball is rising and a steadily increasing downward force of gravity while the ball is decending.
(C) a constant downward force of gravity and a steadily decreasing upward force.
(D) a constant downward force of gravity only.
Problem 40:
The electrons in an atom don't all travel in the lowest energy orbital-the orbital closest to the atom's nucleus. That's because
(A) two identical electrons can never travel in the same orbital.
(B) the electrons are repelled by the nucleus and move away from it.
(C) centrifugal force swings the electrons outward, away from the atom's nucleus.
(D) the nuclear force prevents electrons from approaching the atom's nucleus, so they distribute themselves uniformly among the atom's outer orbitals.
Problem 41:
When you increase the aperture of the lens in your camera, so that it collects more light,
(A) the size of the real image on the film decreases so that the object appears more distant.
(B) the depth of focus increases so that nearby and distant objects are in focus at once.
(C) the depth of focus decreases so that only the object you have focused on is in focus.
(D) the size of the real image on the film increases so that the object appears closer.
Problem 42:
The tank circuit in a radio transmitter helps the transmitter to
(A) move electric current more quickly through its resistor.
(B) move more electric charge up and down the antenna.
(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) store more electric charge in its battery.
Problem 43:
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) electromagnetic waves produced by a magnetron attached to the back wall of the picture tube.
(C) magnetic fields produced by an array of small permanent magnets mounted on the inside surface of the neck of the picture tube.
(D) magnetic fields produced by currents flowing through wire coils on the neck of the picture tube.
Problem 44:
The power company uses a step-up transformer to prepare electric power for delivery to a distant city. The secondary coil of this transformer has many more turns than its primary coil. As a result, the transformer's secondary circuit
(A) has a much higher current but a much lower voltage than its primary circuit.
(B) has a much higher voltage and a much higher current than its primary circuit.
(C) has a much lower voltage and a much lower current than its primary circuit.
(D) has a much higher voltage but a much lower current than its primary circuit.
Problem 45:
Red light has a lower frequency than blue light, so you know that, in empty space,
(A) blue light travels faster than red light.
(B) red light has a shorter wavelength than blue light.
(C) blue light has a shorter wavelength than red light.
(D) red light travels faster than blue light.
Problem 46:
When you see colors reflected from the face of a soap bubble, you are seeing what happens when
(A) a light wave follows two paths to your eye and the two halves of that wave interfere with one another.
(B) light refracts as it passes through the thin, uniform layer of soapy water on the outside of the bubble.
(C) light is bent as it passes through the bubble, as though through a ball of glass or a glass lens.
(D) light reflects from the individual colored soap molecules in the bubble.
Problem 47:
Two adjacent atoms in a polymer molecule are held together by a covalent bond. If you compare the overall potential energy of the molecule before and after this covalent bond forms, you'll find the potential energy after the bond forms is
(A) either more or less than the potential energy before the bond forms, but not the same as the potential energy before the bond forms.
(B) more than the potential energy before the bond forms.
(C) the same as the potential energy before the bond forms.
(D) less than the potential energy before the bond forms.
Problem 48:
If you exert a force of 100 N on a heavy file cabinet as it accelerates forward, it will push back on you with
(A) a force of 100 N.
(B) a force of less than 100 N.
(C) a force of more than 100 N.
(D) zero force until it comes to a stop.
Problem 49:
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) an electric field created by the changing magnetic field of the transformer.
(B) a magnetic field created by the changing electric field of the transformer.
(C) the transformer's capacitor, which stores electrostatic potential energy.
(D) microwaves emitted by the transformer's primary coil; conveying energy from the primary circuit to the secondary circuit.
Problem 50:
You are pushing sideways on the edge of a merry-go-round with a steady force. You are thus exerting a steady torque on the merry-go-round. As a result, the merry-go-round's
(A) angular acceleration is constant.
(B) angular acceleration is increasing.
(C) angular velocity is constant.
(D) angular acceleration is decreasing.
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 electric 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 electric power the hairdryer
is using (you don't have to do this calculation; just describe
how to calculate it)?
(B) Like most electric conductors, the heating coil in the hairdryer
obeys Ohm's law. When a downed tree breaks a nearby power line,
the voltage at your electric 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) As your hair dries out, it gradually becomes stiffer. You
hair is a polymer that dissolves lots of water. Why does getting
your hair wet make it softer?
(D) You are brushing your hair with a cheap metal comb. The comb
gets tangled in your hair and you pull hard, permanently bending
several of the comb's teeth. What happened to the arrangement
of atoms in the teeth as the teeth bent?
(E) You put down the bent metal comb and pick up another comb
that's made of a hard, glassy plastic. This time when you pull
on the comb after it becomes tangled in your hair, several of
its teeth break off. Why doesn't this plastic comb bend the way
the metal comb did?
Problem 2:
One way to detect an art forgery is to look for chemical elements in the paint that are not found in other paintings done by the artist. Many modern paint pigments contain elements that aren't present in old paintings, so finding one of these elements in a supposedly old painting is a sure sign that the painting is a fake. One way to discover these inappropriate elements is to use a technique called neutron activation. In this technique, the painting is exposed to neutrons from a nuclear reactor and the neutrons stick to the nuclei of some of the painting's atoms.
(A) What causes the neutrons to stick the nuclei of the atoms?
(B) Once a neutron sticks to the nucleus of an atom, that atom
may become radioactive. Since most nuclei contain neutrons without
being radioactive, why does adding extra neutrons cause many nuclei
to become radioactive?
(C) These radioactive nuclei often decay by emitting an electron
and a neutrino (actually an anti-neutrino). The neutrino zips
off through space without bumping into anything. Why is the neutrino
so unlikely to collide with anything?
(D) The remaining nucleus has a proton replacing one of its neutrons.
How does this change affect the atom that contains the nucleus?
(E) The remaining nucleus is often left with extra energy-it's
in an excited state. It soon emits a gamma ray that is characteristic
of that nucleus. By studying the gamma rays coming from the neutron-activated
painting, scientists can determine exactly which elements it contains
and whether or not the distribution of elements is consist with
those used by the artist. Once the neutron-activation test is
over, the painting must be stored while its radioactivity diminishes.
While most of its radioactivity vanishes within days, it remains
slightly radioactive for a very long time. If it loses most of
its radioactivity in one day, why doesn't it lose the rest in
one more day?
Problem 3:
Your eye is similar to a camera lens. A camera lens forms a real image of the scene in front of it on a sheet of film. Your eye forms a real image of the scene in front of it on your retina.
(A) To form a sharp image of a particular object on the film,
the distance between the camera lens and the film must be carefully
adjusted. Suppose that the camera is focused on an object 3 m
(10 feet) away. If the object moves farther from the camera, which
way must the lens move so that a real image of that object forms
on the film-toward the film or away from it?
(B) The lens in your eye can't move toward or away from your retina.
Instead, it changes its curvature. Its middle can either bulge
outward to make it more curved or it can squeeze inward to make
it flatter. As the object you are watching moves away from you,
how should the lens of your eye change so that a real image of
the object forms on your retina-should its middle bulge outward
more or squeeze inward more?
(C) When a person is farsighted, the light rays from a nearby
object focus after the retina and the person's vision is blurry.
With the help of eyeglasses, this person's vision can be corrected
so that the person sees a sharp image of the nearby object. To
correct the person's vision of nearby objects, should those eyeglasses
contain converging lenses or diverging lenses?
(D) On a bright day, the pupil of your eye is very small and only
a small fraction of the light reaching your eye goes through your
lens to your retina. What effect does this situation have on your
depth of focus?
(E) When you select eyeglasses, you have the choice of buying
high index of refraction plastic lenses. These lenses are 40%
thinner than normal plastic lenses because the high index of refraction
plastic bends light more than normal plastic. How does this increased
index of refraction affect the amount light that these lenses
reflect?
Problem 4:
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 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 can't 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 doesn't
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?
(E) While you cut the grass, the hot sun gives you a sunburn.
The next time you cut the grass, you remember to put on sunscreen,
a chemical that absorbs ultraviolet light but leaves visible light
essentially unaffected. Why does ultraviolet light cause so much
more trouble to your skin than visible light does?
Problem 5:
You've just been involved in an accident southbound on Rt. 29 and are being questioned by a police officer. However, this officer is a former physics professor who exchanged the ivory tower for a badge and expects your description of the accident to be well-stated in terms of physics concepts. Luckily, you are a student in Physics 106N and this task should be no problem. Right?
(A) You explain to the officer that you were traveling south on
29 at 45 mph in the middle lane when you saw the light turn red
and hit the brakes. In what direction were you accelerating as
you slowed down?
(B) While you were sitting at the light, you were rear-ended by
a drunk driver. The driver's car slammed into your car from behind
and pushed it 50 feet forward. The officer points out that the
drunk's car transferred energy to your car during this collision.
How did the officer know this?
(C) The collision pushed your car across the intersection and
into a brick wall. As you hit the wall, you came to an abrupt
halt but the wall didn't move. The officer asks whether your car
transferred any energy to the wall. What is the correct answer?
Why?
(D) When the front of your car hit the brick wall, you were thrown
forward toward the steering wheel. What caused you to go forward
relative to the car?
(E) Luckily, your airbag was working and helped save your life.
Why did hitting the airbag hurt less than hitting the steering
wheel?