Physics 106 - How Things Work - Spring, 1998

Final Examination

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:

A rubber car tire cannot be melted for recycling because

(A) it contains so much stored elastic potential energy that it spontaneously bursts into flames shortly after transforming into a liquid.
(B) all black materials, including soot, charcoal, graphite, and car tires, don't melt.
(C) it is actually one enormous molecule and cannot become a liquid.
(D) the molecules from which it's composed do not form crystals and only crystalline materials can melt to form liquids.

Problem 2:

One way to thicken a sauce that you are cooking is to add starch to it. The added starch prevents the sauce from flowing easily because starch molecules

(A) are huge chain-like or tree-like structures that entangle one another and bind the sauce together.
(B) vibrate more strongly than most molecules and absorb energy from the rest of the sauce. Without its usual thermal energy, the sauce becomes thicker because it doesn't move easily.
(C) are magnetic and form magnetic domains within the sauce. These domains inhibit slip and make it difficult for the sauce to deform.
(D) are electrically charged, positive and negative, and attract one another with electrostatic forces throughout the sauce.

Problem 3:

For a nuclear weapon to explode normally, the fissionable material in its core must be assembled very quickly. For technical reasons, a nuclear bomb developed by a terrorist group would probably not achieve such rapid assembly. As a result of its slow assembly, such a bomb would

(A) explode powerfully, but at a relatively unpredictable moment. To shorten the time window over which the explosion could occur, external nuclear triggers would be needed.
(B) not explode because there would not be enough momentum present to push the neutrons into the fissionable nuclei of its core.
(C) overheat and push itself apart during the assembly, producing only a weak explosion.
(D) not explode because there would not be enough energy present to push the neutrons into the fissionable nuclei of its core.

Problem 4:

A bright beam of light from a laser passes through a tiny pinhole on its way to a projection screen on the other side of the room. Since the beam was several millimeters in diameter, the pinhole blocks most of the beam's light. After passing through this pinhole, the remaining light

(A) converges together rapidly to form an image of the laser on the projection screen.
(B) forms an extremely narrow beam that illuminates only a tiny spot on the projection screen-a spot the same diameter as the pinhole.
(C) changes frequency and color because it experiences destructive interference inside the pinhole.
(D) spreads relatively rapidly so that it forms a rather large spot on the projection screen.

Problem 5:

You are hosting a romantic candlelight dinner in your room, but you forgot to buy the candles and all the stores are closed. Your desk lamp is too white and too bright to provide the right ambience, so you modify it by inserting a diode between one of the power wires and the bulb. As the result of this change, the lamp emits a reddish glow that's roughly half a bright as without the diode. Just for fun, you reverse the diode so that the end that used to connect to the AC power wire is now connected to the bulb and vice versa. As the result of this reversal, the lamp

(A) emits a deep reddish glow that is roughly half as bright as before you reversed the diode and a quarter as bright as without the diode at all.
(B) no longer glows at all because no current flows through the diode.
(C) still emits the same reddish glow that it emitted before you reversed the diode.
(D) emits a brilliant bluish glow that's roughly twice as bright as without the diode.

Problem 6:

A softball weighs about twice as much as a baseball. Suppose that a softball and a baseball roll off a horizontal table at the same speed and soon hit the horizontal floor. In that case, the

(A) two balls will land at about the same distance from the edge of the table.
(B) lighter baseball will land about half as far from the edge of the table as will the heavier softball.
(C) heavier softball will land about half as far from the edge of the table as will the lighter baseball.
(D) heavier softball will land much, much closer to the edge of the table than will the lighter baseball.

Problem 7:

While low pressure sodium vapor lamps are the most energy efficient light sources commonly available, producing a pure orange-yellow light with a wavelength of 590 nanometers, high pressure sodium vapor lamps produce a richer spectrum of light that is more pleasing to the eye. One effect that contributes to this richer spectrum is

(A) interference-in which light traveling to your eye via several paths within the lamp becomes brighter or darker, depending on how its electric fields interact with one another.
(B) radiation trapping-in which the 590 nanometer light has trouble escaping from the lamp.
(C) thermionic emission-in which electrons in the hot electrodes enter the gas of the discharge.
(D) dispersion-in which the different colors of light travel at different speeds within the lamp.

Problem 8:

Increasing the diameter of a camera lens, while keeping its focal length unchanged, does more than just brighten the image on the film so that you can use a shorter exposure. It also

(A) decreases the depth of focus so that objects at different distances will no longer all be in focus at once.
(B) increases the size of the image on the film so that you get a close up.
(C) decreases the size of the image on the film so that you get a wide angle view.
(D) increases the depth of focus so that objects at different distances will all be in focus at once.

Problem 9:

You are pushing a file cabinet across the floor in a straight line at a steady speed. Which of the following statements about the forces acting on the file cabinet is correct?

(A) The magnitude of the force that you're exerting on the file cabinet must be more than the magnitude of the force that friction is exerting on it.
(B) The magnitude of the force that you're exerting on the file cabinet must be equal to the magnitude of the force that friction is exerting on it.
(C) The amount of forward force you are exerting on the file cabinet must be more than its weight.
(D) If you were to exert twice as much force on the file cabinet, it would slide across the floor at twice its original speed.

Problem 10:

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) current to the electronics and the other wire returns that current to the batteries.
(B) electric current to the electronics while the other wire carries magnetic poles to the speakers.
(C) electric fields to the electronics and the other wire carries magnetic fields to the electronics.
(D) current to the amplifier while the other wire carries current to the speakers.

Problem 11:

The energy that is released by a nuclear weapon was put into the weapon's fissionable core in the process of

(A) heating and melting the fissionable materials when the core is being fabricated.
(B) assembling each of the core's fissionable nuclei from smaller nuclear pieces.
(C) separating the core's fissionable nuclei from the non-fissionable nuclei with which they are normal found.
(D) raising the core's fissionable materials from deep in the earth where they were mined.

Problem 12:

In which one of the following situations are you doing (positive) work on a sack of flour?

(A) When you carry it horizontally at constant velocity.
(B) When you lower it downward at constant velocity from a high shelf to the floor.
(C) When you drag it horizontally across the floor at constant velocity.
(D) When you hold it motionless above your head.

Problem 13:

Many simple forms of stainless steel cannot be hardened by heat treatment, even though they contain significant amounts of carbon. Regardless of temperature, these simple stainless steels have an austenite crystal structure, the same crystal structure that normal steel has when it is very hot. Carbon doesn't harden austenitic steels because

(A) carbon forms iron carbide or "cementite" in austenitic steels.
(B) carbon forms carbon dioxide in austenitic steels.
(C) carbon is non-magnetic in austenitic steels.
(D) carbon dissolves easily in austenitic steels.

Problem 14:

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 kinetic energy.
(B) The upward momentum is transferred to the earth.
(C) The upward momentum is converted into thermal energy.
(D) The upward momentum is converted into gravitational potential energy.

Problem 15:

A good refracting telescope must use more than one glass lens element to form a real image because

(A) it takes two lens elements to form a real image: one to converge the rays and one to stop the convergence right at the focus.
(B) the magnification obtainable with a single element telescope is so small as to be essentially useless.
(C) dispersion in a single element telescope will cause different colored lights from the same object to focus at different locations.
(D) a single lens element can only form a virtual image and it takes a second lens element to turn that virtual image into a real image.

Problem 16:

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 reflects the microwaves while the normal egg does not.
(C) microwaves transfer heat to food principally through its water molecules.
(D) the dehydrated egg is much less dense than a normal egg and doesn't conduct heat well.

Problem 17:

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) some light is reflected whenever light moves from a sugar granule to air or vice versa. The randomly oriented granules reflect light in all directions.
(C) small sugar grains are more dense than large sugar crystals, and they fluoresce white light when exposed to infrared radiation.
(D) small sugar grains are metallic and act as mirrors, scattering light in all directions.

Problem 18:

A makeup mirror is concave, meaning that it is shaped like a round-bottomed soup bowl that is being viewed from above the dinner table. When you hold the makeup mirror a few inches from your face and look at your reflection, you see an enlarged virtual image of your face. Because of its curved shape, the mirror is bending the reflected light rays so that they diverge

(A) less rapidly and appear to come from a distant virtual image.
(B) more rapidly and appear to come from a distant virtual image.
(C) less rapidly and appear to come from a nearby virtual image.
(D) more rapidly and appear to come from a nearby virtual image.

Problem 19:

The tubes in fluorescent lamps have a white powder on their inner surfaces. This powder

(A) 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.
(B) conducts electricity from one electrode to the other and emits white light as current passes through it.
(C) absorbs ultraviolet light and uses the energy from that light to produce white light.
(D) 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.

Problem 20:

At present, a compact disc can only hold about 1 hour of music. This limit is due in large part to the fact that

(A) a compact disc can't turn faster than about 5 turns per second without experiencing a net torque of zero.
(B) light can't be focused to a spot that is significantly smaller than its wavelength.
(C) 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 the distance between them.
(D) a compact disc can't turn slower than about 5 turns per second without experiencing a net torque of zero.

Problem 21:

Even when the core of a nuclear reactor exceeds critical mass by a small amount, it doesn't overheat immediately. The fission chain reactions build slowly because

(A) the reactor has an enormous thermal mass and it takes many minutes for its temperature to change significantly, even with nuclear heating.
(B) the half-life of uranium is several minutes so it takes at least that long for the reactor core to overheat.
(C) it takes seconds or minutes for a neutron released by one fission to reach another radioactive nucleus and cause it to fission.
(D) some fission neutrons aren't released until seconds or minutes after the fissions that eventually produce them.

Problem 22:

Three different lasers are emitting steady beams of light. Each beam consists of countless copies a single original photon of light. However, not all colors can be emitted by a laser. Which of the following choices is possible for these three lasers?

(A) yellow, green, and blue light
(B) green, blue, and white light
(C) blue, white, and yellow light
(D) white, yellow, and green light

Problem 23:

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) different wavelengths travel at different speeds in most materials.
(B) the same wavelength in air can have different frequencies in a material.
(C) the same frequency in air can have different wavelengths in a material.
(D) the same wavelengths can have different colors.

Problem 24:

If you "cook" a compact disc briefly in a microwave oven,

(A) it becomes hot enough to soften and sparks leap about its surface.
(B) it vibrates back and forth violently in response to the fluctuating electric field.
(C) nothing significant happens because it contains no organic materials.
(D) it becomes permanently magnetized.

Problem 25:

Cotton fibers are essentially pure cellulose, a glassy, crystalline polymer formed from sugar molecules. One reason for spraying water on a cotton shirt just before you iron that shirt is that the water

(A) reflects some of the thermal radiation from the iron so that the cotton doesn't overheat and cross-link ("vulcanize") during ironing.
(B) absorbs microwaves from the iron so that the fabric becomes hotter and flattens more completely during ironing.
(C) removes electrons from the cellulose so that it becomes magnetic and is attracted to the steel bottom of the iron during ironing. This attraction improves the flattening effects of ironing.
(D) acts as a plasticizer, lubricating the polymer molecules so that they can rearrange easily during ironing.

Problem 26:

Compared to the radio waves used in normal radio broadcasts, the microwaves used for satellite transmissions have

(A) higher frequencies and shorter wavelengths.
(B) higher frequencies and longer wavelengths.
(C) lower frequencies and shorter wavelengths.
(D) lower frequencies and longer wavelengths.

Problem 27:

Electricity produced in a generating plant passes through a large step-up transformer. This step-up transformer produces the high voltages needed to send electric power long distances across the countryside. Which of the following is transferred from the transformer's primary coil to its secondary coil while the transformer is operating?

(A) Negative electric charges and power.
(B) Positive electric charges, negative electric charges, and power.
(C) Positive electric charges and power.
(D) Power alone.

Problem 28:

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 lower voltage and a much lower current than its primary circuit.
(C) has a much higher voltage but a much lower current than its primary circuit.
(D) has a much higher voltage and a much higher current than its primary circuit.

Problem 29:

Which of the following can cause a stationary charged particle to accelerate?

(A) A stationary wire that is near the charged particle and that contains a constant electric current.
(B) A stationary, constant electric field.
(C) A constant north pole that is near the charged particle.
(D) A stationary, constant magnetic field.

Problem 30:

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.

Problem 31:

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 but they are chemically indistinguishable from stable atoms.
(B) their nuclei are unstable and they are chemically unstable.
(C) they are chemically unstable but their nuclei are indistinguishable from stable atoms.
(D) each atom emits a steady stream of X-ray radiation.

Problem 32:

There is a metal screen on the front window of a microwave oven. This screen is essential because it

(A) prevents electric charge from accumulating on the window.
(B) prevents the glass from breaking in response to the rapid heating of its inner surface and the thermal stresses that result.
(C) protects the window from splatters that may occur when food inside the oven boils.
(D) reflects microwaves and keeps them inside the oven.

Problem 33:

Two identical spaceships are travelling through deep, empty space and are not experiencing any forces from their surroundings. Their velocities are both constant, but one ship is moving twice as fast as the other. Each ship has a large rocket engine that can be used to push it forward. From this information, it's clear that

(A) both ships have their engines shut off.
(B) the fast ship's engine is pushing forward twice as hard as the slow ship's engine.
(C) both ships' engines are pushing forward equally hard.
(D) the fast ship's engine is pushing forward four times as hard as the slow ship's engine.

Problem 34:

A gymnast is bouncing on a trampoline, rising 2 meters above its surface on every bounce. After the rising gymnast has left the surface of the trampoline but is still heading upward,

(A) the gymnast is not experiencing any upward forces.
(B) the upward force of the gymnast's momentum carries the gymnast upward. This upward force is always stronger than the gymnast's downward weight.
(C) the upward force of the gymnast's momentum carries the gymnast upward. This upward force is always equal in strength to the gymnast's downward weight.
(D) the upward force of the gymnast's momentum carries the gymnast upward. This upward force is initially stronger than the gymnast's downward weight but diminishes to zero as the gymnast rises.

Problem 35:

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 all part of a single wave, while those in sunlight are independent waves.
(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 have both electric and magnetic fields, while those in sunlight have only magnetic fields.
(D) the photons in a laser beam are both vertically and horizontally polarized, while those in sunlight are only vertically polarized.

Problem 36:

Most nuclear reactors in the United States are thermal fission reactors, reactors that slow their fission neutrons by sending those neutrons through materials known as moderators. Water is a common moderator. When a fast moving neutron enters water, it usually slows down because it

(A) drags the water molecules with it and experiences water resistance.
(B) pushes and pulls on the electrons in the water molecules and transfers most of its energy to those electrons.
(C) creates bubbles in the water as it passes and those bubbles carry away most of its energy and momentum.
(D) collides with the water nuclei and transfers most of its energy and momentum to those nuclei.

Problem 37:

You place an aluminum soda can on a hard floor and step on it with your foot, crushing it flat. The act of crushing the can

(A) decreases the can's total energy.
(B) leaves the can's total energy unchanged.
(C) increases the can's total energy.
(D) has an undeterminable effect on the can's total energy.

Problem 38:

Vegetable oil and Pyrex glass have almost exactly the same indices of refraction-the speed of light is the same in both materials. If you submerge a clear Pyrex dish in vegetable oil,

(A) the Pyrex dish will be virtually invisible because no light will reflect from its surfaces.
(B) the surfaces of the Pyrex will appear mirror-like-reflecting light perfectly as the result of total internal reflection.
(C) the Pyrex dish will act as a lens and you will see highly distorted images of objects beyond the dish.
(D) you will see a pattern of beautiful rainbow colors in the glass as dispersion separates white light.

Problem 39:

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

(A) molten quartz (liquid quartz).
(B) crystalline quartz (quartz crystals or quartz sand).
(C) gelatin (unflavored and unsweetened).
(D) steel.

Problem 40:

An engineer at the company you're working for has just reported finding an unusual electromagnetic wave. This wave consists only of an electric field, with no magnetic field accompanying it. You are certain that the engineer is mistaken because

(A) an electromagnetic wave must have a magnetic field that changes with time to produce its electric field.
(B) while waves consisting only of electric fields are common and travels indefinitely through space, they are known as "electric waves," not "electromagnetic waves."
(C) electromagnetic waves always contain both electric charges and magnetic poles, and magnetic poles are accompanied by magnetic fields.
(D) electromagnetic waves contain moving electric charges and charges produce magnetic fields when they move.

Problem 41:

Some of the X-rays emitted by an X-ray imaging machine are fluorescence X-rays and are formed when individual atoms in the machine undergo radiative transitions. While the mercury atoms in a fluorescent lamp also undergo radiative transitions, those mercury atoms emit ultraviolet light, not X-rays. The reason for this difference is that

(A) mercury atoms aren't massive enough to emit X-rays, whereas the atoms in an X-ray machine are.
(B) the electrons in the imaging machine atoms experience much larger changes in energy during their radiative transitions than the electrons in the mercury atoms do.
(C) the electrons in the imaging machine atoms experience much smaller changes in energy during their radiative transitions than the electrons in the mercury atoms do.
(D) the atoms in an X-ray machine are packed together in a solid and can amplify each other's waves much more effectively than the gaseous mercury atoms in a fluorescent lamp can.

Problem 42:

If you float an aluminum pie plate on the surface of a pond and move the north pole of a strong magnet in a clockwise circle just above that plate, the plate will

(A) be lifted out of the water and will stick to the strong north pole above it.
(B) begin turning clockwise, as though it were being dragged along with the magnet.
(C) remain stationary.
(D) begin turning counter-clockwise, as though it were being twisted away from the magnet.

Problem 43:

A glass fiber can act as a pipe for light-light that enters the fiber at its end follows the fiber almost indefinitely without escaping through the fiber's surface. The light follows the fiber because

(A) the fiber contains many tiny converging lenses that focus the light back into the fiber over and over again.
(B) electric charges in the glass attract the light and prevent it from accelerating outward, away from the center of the fiber.
(C) the fiber contains many tiny diverging lenses that focus the light back into the fiber over and over again.
(D) whenever it tries to leave the glass at a shallow angle, it's perfectly reflected.

Problem 44:

The rear windows of some cars have holes in them so that motors inside the cars can operate wiper blades outside the cars. These holes were diamond drilled at the factory before the glass was tempered. If a local car glass company were to try to drill a hole in a car window that had already been tempered,

(A) the diamond drill would be reflected because the speed of light is almost the same in tempered glass as it is in diamond.
(B) the diamond drill would break because tempered glass is much harder than normal glass.
(C) the window would vibrate violently at one of the tones of the "well-tempered" scale and would probably crack.
(D) the window would tear itself into tiny pieces as soon as the drill reached the central portion of glass inside the window.

Problem 45:

You are observing a distant ship with a telescope but you can't quite read the ship's name. To increase the magnification of the telescope, you replace the eyepiece with one having a

(A) longer focal length than before.
(B) smaller aperture than before.
(C) larger aperture than before.
(D) shorter focal length than before.

Problem 46:

You have just put fresh batteries in your flashlight and it's working nicely. Now suppose that you remove all of the batteries and reinsert them backward. Despite the fact that their positive and negative terminals are reversed, the batteries connect properly to one another and to the flashlight, so that there are no connection problems in the flashlight. As the result of this battery reversal, the flashlight will

(A) remain lit regardless of the position of its on-off switch.
(B) work in reverse, lighting up when you put its switch in the "off" position and not lighting up when you put its switch in the "on" position.
(C) work normally, lighting when you switch it "on" and turning off when you switch it "off."
(D) not light up at all, regardless of the position of its on-off switch.

Problem 47:

An expert archer is firing arrows at a target roughly 50 meters away. Each arrow travels almost horizontally and hits the target at over 100 mph. Once an arrow has left the archer's bow, that arrow experiences

(A) no forward horizontal forces.
(B) a forward horizontal force that gradually diminishes in strength as the arrow approaches the target and reaches zero at the moment of impact.
(C) a forward horizontal force that gradually diminishes in strength as the arrow approaches the target but remains reasonably strong even at the moment of impact.
(D) a forward horizontal force that remains constant all the way to the target.

Problem 48:

If you melt quartz (also known as silica or silicon dioxide), it becomes a thick, gooey liquid. If you cool this liquid quickly, it forms a clear solid but if you cool it too slowly, the resulting solid is cloudy. The cloudy solid forms because slow cooling

(A) allows the temperatures to get out of balance, so that the flow of heat within the material fills it with tiny white filaments.
(B) permits stresses to build up within the liquid so that it experiences countless microscopic fractures as it hardens.
(C) allows tiny quartz crystals to form and grow within the supercooled liquid as it hardens.
(D) gives the chemicals time to react and produce tiny white particles within the colorless solid.

Problem 49:

The X-rays used in medical imaging travel through tissue relatively easily but are mostly absorbed by bone. That's because

(A) only neutrons can absorb X-rays and the atoms in bone have many more neutrons than those in tissue.
(B) the atoms in bone are slightly radioactive and the passing X-rays cause them to undergo fission. Since the atoms in tissue are not radioactive, they cannot undergo fission.
(C) solids, such as bone, are much better at absorbing X-ray photons than are liquids, such as those in tissue.
(D) the atoms in bone generally have more tightly bound electrons than those in tissue and are thus able to absorb higher energy photons.

Problem 50:

A glass window pane reflects about 4% of the light striking its front surface because

(A) light slows down upon entering the glass and the resulting impedance mismatch causes some of that light to reflect.
(B) glass is about 16% metallic and this partial conductivity causes a fraction of the light striking glass to reflect.
(C) glass is about 4% metallic and this partial conductivity causes a fraction of the light striking glass to reflect.
(D) glass is about 2% metallic and this partial conductivity causes a fraction of the light striking glass to reflect.

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:

Modern audio amplifiers usually contain at least four important electronic components: resistors, capacitors, diodes, and MOSFETs. Let's take a brief look at each of these devices.

Problem 2:

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.

Problem 3:

Sir Lancelittle headed off to seek his fortune, riding on his noble horse Fleabag and armed only with the legendary sword Whycaliber. Unfortunately, Whycaliber was made of pure lead because it was given to him by the Lady of the Pond and she was into heavy metal.

Problem 4:

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. A common 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.

Problem 5:

You are outdoors on a sunny day, playing with a magnifying glass that is 10 centimeters in diameter, 1.0 centimeter thick, and has a focal length of 20 centimeters.

Problem 6:

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.