Gerner, Physical Science, Exam 3
How could a lightbulb near, yet not touching, an electromagnet be lit? Is ac or dc required?
If the light bulb is connected to a wire loop that intercepts changing magnetic field lines from an electromagnet, voltage will be induced which can illuminate the bulb. Change is the key, so the electromagnet should be powered with ac.
What is a magnetic domain?
A magnetic domain is a region of aligned iron atoms.
How much unpolarized light does an ideal Polaroid filter transmit?
An ideal Polaroid will transmit half of unpolarized light.
Which has the higher frequency: red light or blue light?
Blue light has a higher frequency than red light.
What is meant by saying that charge is conserved?
Conservation of charge means charge cannot be created or destroyed, but merely transferred.
Which of the following will not induce a voltage in a loop of wire? A. Move the loop near a magnet. B. Move a magnet near the loop. C. change the current in a nearby loop. D. All of these will induce a voltage.
D. All of these will induce a voltage.e
What two kinds of motion are exhibited by electrons in an atom?
Electron spin and electron revolution about the nucleus.
In one word, what is it that moves from source to receiver in wave motion?
Energy.
Which of the following is false? A. An electrical conductor has little electrical resistance. B. Temperature increases electrical resistance. C. A thick wire would have lower resistance than a thin wire of the same length. D. Increasing the length of a wire increases its resistance. E. A superconductor has no electrical resistance. F. None of these.
F. None of these.
What two physics mistakes occur in a science-fiction movie that shows a distant explosion in outer space that you see and hear at the same time.
First, in outer space there is no air or other material to carry sound. Second, if there were, the faster- moving light would reach you before the sound.
Is glass transparent or opaque to light of frequencies that match its own natural frequencies?
Glass is opaque to frequencies of light that match its own natural frequencies. This is because the electrons in the absorbing medium are driven to oscillations of much larger amplitudes than occurs for non-resonant frequencies. These large amplitudes result in energy transfer to neighboring atoms and an increase in thermal energy rather than a re-emission of light.
Give two examples of common force fields.
Gravitational and electric. (Magnetic fields also)
If the frequency of a sound is doubled, what change occurs in its speed? What change occurs in its wavelength?
If the frequency of sound is doubled, its speed will not change at all, but its wavelength will be "com- pressed" to half size. The speed of sound depends only on the medium through which it travels, not on its frequency, wavelength, or intensity (until the intensity gets so great that a shock wave results).
Two charged particles are projected into a magnetic field that is perpendicular to their velocities. If the charges are deflected in opposite directions, what does this tell you about the particles?
If the particles enter the field moving in the same direction and are deflected in opposite directions (say one left and one right), the charges must be of opposite sign.
Compared to the distance of an object in front of a plane mirror, how far behind the mirror is the image?
Image distance and object distance are the same.
Why is iron magnetic and wood not magnetic?
Iron has magnetic domains, wood does not.
When steel naval ships are built, the location of the shipyard and the orientation of the ship while in the shipyard are recorded on a brass plaque permanently fixed to the ship. What does this have to do with magnetism?
Just as a nail is magnetized by beating on it, an iron ship is beat upon in its manufacture, making it a permanent magnet. Its initial magnetic field orientation, which is a factor in subsequent magnetic measurements, is in effect recorded on the brass plaque.
What is the relationship between refraction and the speed of light?
Light speed slows when refracted in a medium.
Does light travel faster in thin air or in dense air? What does this difference in sped have to do with the duration of daylight?
Light travels faster in thin air. This difference in speed accounts for refraction of sunlight, particularly when the sun is on the horizon where it appears higher in the sky. So the duration of daylight is extended.
Will light pass through a pair of Polaroid filters when their air axes are aligned? When their axes are at right angles to each other?
Light will pass through the pair when their axes are aligned, but not when the axes are at right angles to each other.
In what way is the rule for the interaction between magnetic poles similar to the rule for the interaction between electric charges?
Like poles repel; opposite poles attract.
In what way are magnetic poles very different from electric charges?
Magnetic poles cannot be isolated.
In what direction relative to a magnetic field does a charged particle move in order to experience maximum deflecting force? Minimum deflecting force?
Maximum deflecting force when the charged particles move perpendicular to the magnetic field; minimum deflecting force when the particles move parallel to the field.
What important connection did Maxwell discover about electric and magnetic fields?
Maxwell discovered that the mutual induction of electric and magnetic fields produced electromagnetic waves. He discovered the nature of light!
What are the three ways in which voltage can be induced in a loop of wire?
Move the loop near a magnet; move a magnet near a loop; change the current in a nearby loop.
What produces a magnetic field?
Moving electric charges produce a magnetic field.
Is it correct to say that a generator produces energy?
No, A generator transforms energy from one form to another.
Does the medium in which a wave travels move with the wave?
No, for the propagation of energy travels, not the medium itself.
Can an efficient transformer step up energy?
No, no, no, a thousand times no! No device can step up energy. This principle is at the heart of physics. Energy cannot be created or destroyed.
A balloon may easily be charged to several thousand volts. Does that mean it has several thousand joules of energy?
No. Several thousand volts is different than the ratio several thousand volts per coulomb. Voltage is measured in volts; voltage/coulomb is energy and measured in joules.
What does it mean to say that one wave is out of phase with another?
One wave is out of step with another.
In the Doppler effect, does frequency change? Does wavelength change? Does wave speed change?
Only frequency and wavelength changes in the Doppler effect, not wave speed.
The person's eye at point P looks into the mirror. Which of the numbered cards can she see reflected in the mirror.
Only light from card number 2 reaches her eye.
What is the color of the peak frequency of solar radiation? TO what color of light are our eyes most sensitive/
Peak frequency of sunlight is yellow-green, which is also the color that our eyes are most sensitive to.
Distinguish among these characteristics of a wave: period, amplitude, wavelength, and frequency.
Period is the time for a complete cycle to occur; amplitude is the maximum displacement from the midpoint of a wave to the crest (or trough), wavelength is the distance between successive crests, troughs, or identical parts of a wave, and frequency is the number of vibrations per unit time.
Is polarization a property of transverse waves, longitudinal waves, or both?
Polarization is a property of transverse waves, never longitudinal waves.
how does the Doppler effect aid police in detecting speeding motorists?
Police use radar waves which are reflected from moving cars. From the shift in the returned frequen- cies, the speed of the reflectors (car bodies) is determined.
To make a compass, point an ordinary iron nail along the direction of Earth's magnetic field and repeatedly strike it for a few seconds with a hammer or a rock. Then suspend it at its center of gravity by a string. Why does the act of striking magnetize the nail?
Pounding on the nail shakes up the domains, allowing them to realign themselves with Earth's magnetic field. The result is a net alignment of domains along the length of the nail. (Note that if you hit an already magnetized piece of iron that is not aligned with Earth's field, the result can be to weaken, not strengthen, the magnet.)
What are the three primary colors? The three subtractive primary colors?
RGB are primary. CMY are subtractive
What do radio waves and light have in common? What is different about them?
Radio waves travel at the speed of every other electromagnetic wave—the speed of light. Don't con- fuse radio waves with the sound waves they can make.
Relate wave speed and bending to the phenomenon of refraction.
Refraction occurs when parts of the wave fronts of sound travel at different speeds and produce bending in the direction of the waves.
Why does the sun look reddish at sunrise and sunset?
Scattering of high-frequency blue light occurs all along the path of sunlight, so the long path at sunrise or sunset finds much blue missing. What remains is light of lower frequencies, which accounts for the reddish color of the Sun at these times.
How much energy is given to each coulomb of charge passing through a 6-V battery?
Six joules of energy are given to each coulomb of charge passing through a 6-V battery.
Does sound tend to bend upward or downward when it travels faster near the ground than higher up?
Sound bends upward
Stare at a piece of colored paper for 45s or so. Then look at a plain white surface. The cones in your retina that are receptive to the color of the paper become fatigued, so you see an afterimages of the complementary color when you look at a white area. This is because the fatigued cones send a weaker signal to the brain. All the colors produce white, but all the colors minus one produce the color that is complementary to the missing color.
Staring at a flag is also a good activity. After a long stare, looking at a white surface produces the flag in its complementary colors.
What commonly supplies the energy input to a turbine?
Steam.
Why is the lettering on the front of some vehicles-for example, ambulance- "backward"?
Such lettering is seen in proper form in the rearview mirrors of cars ahead.
Can the Doppler effect be observed with longitudinal waves, with transverse waves, or with both?
The Doppler effect can occur with both longitudinal and transverse waves.
Hold a pocket mirror almost at arm's length from your face and note the mount of your face you can see. To see more of your face, should you hold the mirror closer to farther, or would you have to have a larger mirror?
The amount of your face you can see is twice the size of the mirror—whether you hold the mirror close or at arm's length. (You can win bets on this question!)
What is the angle between a light ray and its wavefront?
The angle is always 90 degrees.
What is the law of reflection for sound?
The angle of incidence is equal to the angle of reflection.
How does the average speed of light in glass compare with its speed in a vacuum.
The average speed of light in glass is less than its speed in a vacuum.
What are the basic differences and similarities between a generator and an electric motor?
The basic differences are input and output, so whereas a motor converts electrical energy into mechanical energy, a generator does the reverse.
How does the charge of one electron compare with the charge of another electron?
The charges are identical for all electrons.
What is the evidence for a cloud being composed of particles having a variety of sizes?
The colors of light scattered from particles vary with particle size. The whiteness of clouds is evidence of a wide spectrum of colors scattered from particles of a wide variety of sizes.
What colors of ink do color ink-jet printers use to produce a full range of colors? Do the colors form by color addition or by color subtraction?
The colors used are magenta, cyan, yellow, and black. Colors are formed by color subtraction.
How does the total current through the branches of a parallel circuit compare with the current through the voltage source?
The current through the voltage source is the sum of the currents in the branches.
In a dress shop with only fluorescent lighting, a customer insists on taking dresses into the daylight at the doorway to check their color. Is she being reasonable?
The customer is being reasonable in requesting to see the colors in the daylight. Under fluorescent lighting, with its predominant higher frequencies, the bluer colors rather than the redder colors will be accented. Colors will appear quite different in sunlight.
How is the direction of an electric field defined?
The direction of an electric field is the direction of force on a positive charge.
What is the fate of the energy in ultraviolet light incident on glass?
The energy of ultraviolet light becomes thermal energy.
Why is the magnetic field strength inside a current carrying loop of wire greater than the field strength about a straight section of wire?
The fields overlap inside the loop and strengthen the magnetic field strength.
How can a certain note sung by a singer cause a crystal glass to shatter?
The glass will shatter by resonance, when the buildup of vibrations in the glass exceed the breaking point of the glass.
What prevents rainbows from being seen as complete circles?
The ground gets in the way, cutting of viewing a whole circular rainbow.
State Faraday's law.
The induced voltage in a coil is proportional to the number of loops, multiplied by the rate at which the magnetic field changes within those loops.
In what sense does the law of reflection hold for a diffuse reflector?
The law of reflection holds locally at each tiny part of the irregular surface, but not for the diffuse sur- face as a whole.
What is the shape of a magnetic field about a current carrying wire?
The magnetic field about a current-carrying wire take the shape of circles.
What happens to the direction of the magnetic field about an electric current when the direction of the current is reversed?
The magnetic field also reverses direction.
If you rub an inflated balloon against your hair and place it against a door, by what mechanism does the balloon stick?
The mechanism of sticking is charge induction. If it's a metal door, the charged balloon will induce an opposite charge on the door. It will accomplish this by attracting opposite charges to it and repelling like charges to parts of the door farther away. The balloon and the oppositely-charged part of the door are attracted and the balloon sticks. If the door is an insulator, the balloon induces polarization of the molecules in the door material. Oppositely-charged sides of the molecules in the surface of the door face the balloon and attraction results. So whether you consider the door to be an insulator or a con- ductor, the balloon sticks by induction.
As more lines as opened at a fast-food restaurant, the resistance to the motion of people trying to get served is reduced. how is this similar to what happens when more branches are added to a parallel circuit?
The more branches in both cases, the less the overall resistance.
Which part of an atom is positively charged, and which part is negatively charged?
The nucleus and its protons are positively charged; electrons are negatively charged.
How does the number of protons in the atomic nucleus normally compare with the number of electrons that orbit the nucleus?
The numbers of protons and electrons are normally equal.
What physics principle does Manuel use when he pumps in rhythm with the natural frequency of the swing?
The physical principle is resonance.
What is the principal difference between a radio wave and light? Between light and x-rays?
The principal difference between radio, light and x-rays is frequency.
What is the relationship among electric power, current, and voltage?
The relationship is given by the formula, power=current x voltage.
In periods of peak demand, power companies lower their voltage in order to save them power (and save you money)! TO see the effect, consider a 1200-W toaster that draws 10 A when connected to 120 V. Suppose the voltage is lowered 10% to 108V. By how much does the current decrease? By how much does the power decrease? (Caution: The 1200-W label is valid only when 120 V is applied. When the voltage is lowered, the resistance of the toaster, not its power, remains constant.)
The resistance of the toaster is R=V/I= 120V/10A=12W. So when 108 V is applied, the current is I=V/R=108V/12W=9A and the power is P=IxV=(9A)(108V)=972 W, only 81 percent of the normal R 12W power. (Can you see the reason for 81 percent? Current and voltage are both decreased by 10 percent, and 0.9 x 0.9= 0.81.)
In what region of the electromagnetic spectrum is the resonant frequency of electrons in glass?
The resonant frequency of glass is in the ultraviolet region.
In a circuit consisting of two lamps connected in series, if the current in one lamp is 1 A, what is the current in the other lamp?
The same, for the same current passes through each lamp that is connected in series.
Why does the sky normally appear blue?
The sky appears blue because blue is the most scattered color of sunlight.
Why does a struck tuning fork sound louder when its handle is held against a table?
The sound is louder when the struck tuning fork is held against a table because a greater surface is set into vibration.
How does the speed of sound in water compare with the speed of sound in the air? How does the speed of sound in steel compare with the speed of sound in air?
The speed of sound in water is about four times that in air. For steel, about 15 times as much as in air.
Does a lamp with a thick filament draw more current or less current than a lamp with a thin filament?
The thick filament has less resistance and will draw (carry) more current than a thin wire connected across the same potential difference. (Important point: It is common to say that a certain resistor "draws" a certain current, but this may be misleading. A resistor doesn't "attract" or "draw" current, just as a pipe in a plumbing circuit doesn't "draw" water; it instead "allows" or "provides for" the passage of current when an electrical pressure is established across it.)
What is the function of the third prong on the plug of an electrical appliance?
The third prong is connected to the "ground," providing a route for unwanted charge. It prevents charge buildup on the appliance.
When Tim pushes the wire between the poles of the magnet, the galvanometer registers a pulse. When he lifts the wire, another pulse is registered. How do the pulses differ?
The two pulses are opposite in direction. When the wire enters the magnetic field between the poles of the magnet, a pulse of voltage is induced in the wire, which is indicated by movement of the galvanometer needle. When the wire is lifted a pulse in the opposite direction is induced, and the needle moves in the opposite direction.
What is the unit of electrical resistance?
The unit of electrical resistance is the ohm, symbol (omega)
If 6-V were impressed across the circuit in the previous question, and the voltage across the first lamp were 2 C, what would be the voltage across the second lamp?
The voltage across the second lamp would be 4 V, so the sum of the two 6 V.
Which have the longest wavelength: light waves, X-rays, or radio waves?
The wavelengths of radio waves are longer than those of light waves, which are longer than the wave- lengths of X-rays.
A car's headlight dissipates 40 W on low beam and 50 W on high beam. Is there more or less resistance in the high-bema filament.
There is less resistance in the higher wattage lamp. Power=currentxvoltage. More power for same voltage=more current. more current for same voltage=less resistance.
What kind of motion should you impart to a stretched coiled spring to produce a transverse wave? A Longitudinal wave?
To produce a transverse wave with a Slinky, shake it to and fro in a direction that is perpendicular to the length of the Slinky itself (as with the garden hose in the previous exercise). To produce a longitu- dinal wave, shake it to and fro along the direction of its length, so that a series of compressions and rarefactions is produced.
What determines whether a material is transparent or opaque?
Transparency or opaqueness is determined by the match between incident light frequencies and the resonant frequency of the material. A substance that is transparent to a range of light frequencies will be opaque to those frequencies that match its own resonant frequency.
Why do troops "break step" when crossing a bridge.
Troops break step in order to avoid marching in rhythm with the natural frequency of the bridge, to prevent resonance.
What do we call two colors that add to produce white?
Two colors that add to produce white are called complementary colors.
In what direction are the vibrations in a transverse wave, relative to the direction of wave travel? In longitudinal wave?
Vibrations in a transverse wave are perpendicular to wave travel, and parallel to wave travel in longi- tudinal waves.
Red light has a longer wavelength than violet light. Which has the higher frequency?
Violet light has the greater frequency.
Distinguish between constructive interference and destructive interference.
Wave amplitude is increased in constructive interference; reduced in destructive interference.
What is the relationship among frequency, wavelength, and wave speed?
Wave speed is equal to the product of frequency and wavelength; v=f(wavelength)
What kind of charge does an object acquire when electrons are stripped from it?
When electrons are stripped from an object, it is left with a positive charge.
What is the effect on current through a circuit of steady resistance when the voltage is doubled? When both voltage and resistance are doubled?
When only voltage is doubled, current is also doubled. If both voltage and resistance are doubled, the current doesn't change.
What percentage of light is transmitted by two ideal Polaroid filters, one on top of the other with their polarization axes aligned? With their polarization axes at right angles to each other?
With polarization axes aligned, a pair of Polaroids will transmit all components of light along the axes. Half of the light gets through the first Polaroid, and all of that get through the second. So that's half, or 50%. With axes at right angles, no light will be transmitted.
Do a pair of parallel current-carrying wires exert forces on each other?
Yes, each will experience a force because each is in the magnetic field generated by the other. Interestingly, currents in the same direction attract, and currents in opposite directions repel.
Does the law of reflection hold for curved mirrors?
Yes, the law of reflection holds locally at each tiny part of the curved surface, but not for the curved mirror as a whole.
How can a single polaroid filter be used to show that the sky is partially polarized?
You can determine that the sky is partially polarized by rotating a single sheet of Polaroid in front of your eye while viewing the sky. You'll notice the sky darken when the axis of the Polaroid is perpen- dicular to the polarization of the skylight.
Your tutor tells you than an ampere and a volt really measure the same thing, and the different terms only make a simple concept seem confusing. Why should you find another tutor?
Your tutor is wrong. An ampere measures current, and a volt measures electric potential (electric pres- sure). They are entirely different concepts; voltage produces amperes in a conductor.
What is a reverberation?
A reverberation is sound from multiple reflections.
Which has a greater resistance: A thick wire or a thin wire of the same length?
A thin wire has a greater resistance (just as a thin pipe greater resists water flow).
What kinds of waves exhibit interference?
All kinds of waves exhibit interference.
Which of the following is false? A. The study of sound properties is called acoustics. B. The refraction of sound is called an echo. C. Dolphins use ultrahigh-frequency sound to locate objectives in their environment; fish hear mainly low-frequencies. D. Refraction occurs when parts of the wave fronts travel at different speeds. E. None of these.
B. The REFLECTION of sound is an echo.
How much energy is given to each coulomb of charge passing through a 12 volt battery? (Volt=J/C) A. 1 Joule B. 6 Joules C. 12 Joules D. 24 Joules
C. 12 Joules
Distinguish between dc and ac.
Direct current, moving in one direction, is dc. Alternating current, moving to and fro, is ac.
Which has greater electrical resistance: wet skin or dry skin?
Dry skin has considerably more electrical resistance than wet skin.
What condition is necessary for a sustained flow of electric charge through a conducting medium?
A sustained flow needs a sustained difference in potential across a conducting medium, such as a battery or generator.
Which of these does a transformer change: voltage, current, energy, power?
A transformer changes voltage and current, but not energy and power.
How does the magnitude of electrical force between a pair of charged particles change when the particles are moved twice as far apart? Three times as far apart?
By the inverse-square law, particles twice as far apart have 1/4 the force; three times as far apart, 1/9 the force.
How are frequency and period related?
Frequency and period are the inverse of each other.
All bulbs are identical in the circuits shown. A voltmeter is connected across a single bulb to measure the voltage drop across it. Rank the voltage readings from highest to lowest.
A, B, C
Note the four pairs of transverse wave pulses that move toward each other. At some point in time the pulses meet and interact with each other. Rank the four pairs from highest to lowest, on the basis of the height of the peak that results when the centers of the pulses coincide.
A, B, D, C.
If sound becomes louder, which wave characteristic is likely increasing: frequency, wavelength, amplitude, or speed?
Amplitude.
What is induced by the rapid alternation of a magnetic field?
An alternating electric field is induced.
What is induced by the rapid alternation of an electric field?
An alternating magnetic field is induced.
How is Coulomb's law similar to Newton's law of gravitation? How is it different?
Both laws are inverse-square laws. How they differ is mainly that gravitation is only attractive, whereas electrical forces can repel.
Distinguish between forced vibrations and resonance.
Forced vibrations occur when a surface is forced to vibrate. When the forcing frequency matches the natural frequency of the surface, the result is resonance.
By what specific means do the bits of fine threads align in the electric fields in figure 8.11?
The bits of thread become polarized in the electric field, one end positive and the other negative, and become the electric counterparts of the north and south poles of the magnetic compass. Opposite forces on the end of the fibers (or compass needle) produce torques that orient the fibers along the field direction (look ahead to Figure 9.4 in the next chapter).
Suppose that the strength of the electric field about an isolated point charge has a certain value at a distance of 1 m. How does the electric field strength compare at a distance of 2 m from the point charge? What law guides your answer?
(a) The forces on the electron and proton will be equal in magnitude, but opposite in direction. (b) Because of the greater mass of the proton, its acceleration will be less than that of the electron. How much less? Since the mass of the proton is nearly 2000 times that of the electron, its acceler- ation will be about 1/2000 that of the electron. The greater acceleration of the electron will be in the direction opposite to the electric field. (c) The electron and proton accelerate in opposite directions.
Does a battery produce dc or ac? Does the generator at a power station produce dc or ac?
A battery produces dc. A generator normally produces ac.
Which of the following is false? A. When connected to the same voltage, a lamp with a thicker filament will draw less current than a lamp with a thinner filament. B. As temperature increases, so does resistance. C. A superconductor has zero electrical resistance. D. Resistance increases as the length of a wire increases. E. None of these.
A is false. The correct was to word this would be: A lamp with a thinner filament will draw less current than a lamp with thicker filament.
What is a mirage?
A mirage is a distorted view wherein refracted light appears is if it is reflected light.
How is the strength of a magnetic field in a coil affected when a piece of iron is placed inside?
A piece of iron strengthens the electromagnet because alignment of domains in the piece of iron adds to the overall field.
In what sense can a transformer be through of as an electrical lever? What does it multiply? what does it not multiply?
A transformer is analogous to a mechanical lever in that work is transferred from one part to another. What is multiplied in a mechanical lever is force, and in an electrical lever, voltage. In both cases, energy and power are conserved, so what is not multiplied is energy, a conservation of energy no-no!
In a series circuit with a 2 Ohm and a 4 Ohm light bulb, if the voltage drop across the 2 Ohm light bulb is 6 V, which of the following is true? A. The voltage drop across the 4 Ohm light bulb is greater than 6 V. B. The voltage drop across the 4 Ohm light bulb is equal to 6 V. C. The voltage drop across the 4 Ohm light bulb is less than 6 V.
A. The voltage drop across the 4 Ohm light bulb is greater than 6 v.
Rank the circuits according to the brightness of the indentical bulbs, from brightest to dimmest.
A=B=C (They are all the same brightness)
All the bulbs in the three circuits are identical. An ammeter is placed in different locations, as shown. Rank the current readings in the ammeter from highest to lowest.
A=B=C (They are all the same)
All atoms have moving electric charges. Why, then, aren't all materials magnetic?
All magnetism originates in moving electric charges. For an electron there is magnetism associated with its spin about its own axis, with its motion about the nucleus, and with its motion as part of an electric current. In this sense, all magnets are electromagnets.
What is the law of reflection?
Angle of incidence equals angle of reflection.
At the security area of an airport you walk through a metal detector, which consists of a weak ac magnetic field inside a large coil of wire. If you forget to take keys out of your pocket as you pass through the detector, or if you wear a pacemaker, why is an alarm sounded.
As in the previous answer, eddy currents induced in the metal change the magnetic field, which in turn changes the ac current in the coils and sets off an alarm.
Your physics instructor drops a magnet through a long vertical copper pipe and it moves slowly compared with the drop of a nonhmagnetized object. Provide an explanation.
As the magnet falls, it induces current that circles in the conducting pipe and is accompanied by its own magnetic field. The moving magnet is slowed by interaction with this induced field.
How does the Doppler effect used in radar guns give the speeds of tennis balls and baseballs at sporting events?
As with the previous question, radar waves are reflected from moving balls. From the shift in the returned frequencies, the speed of the balls is determined and displayed.
You dip your finger at a steady rate into a puddle of water to make waves. What happens to the wavelength if you dip your finger more frequently?
As you dip your fingers more frequently into still water, the waves you produce will be of a higher fre- quency (we see the relationship between "how frequently" and "frequency"). The crests of the higher- frequency waves will be closer together—their wavelengths will be shorter.
If you place a chunk of iron heart the north pole of a magnet, attraction will occur. Why will attraction also over if you place the same iron near the south pole of the magnet?
Attraction will occur because the magnet induces opposite polarity in a nearby piece of iron. North will induce south, and south will induce north. This is similar to charge induction, where a balloon will stick to a wall whether the balloon is negative or positive.
Which of the following is false? A. Electrical resistance increases as temperature increases. B. Electrical resistance increases as the length of a wire decreases. C. Electrical resistance increases as the thickness of a wire decreases. D. A superconductor has no electrical resistance.
B is false. Electrical resistance increases as the length of the wire increases.
Which of the following is false? A. If a charged particle is placed in an electric field, it experiences a force. B. Electric field lines from a negative charge attract electric field lines from another negative charge. C. An electric field extends out in space from a charged particle. D. The electric field stores energy.
B is false. They don't attract field lines from another negative charge.
Which of the following is false? A. A charged particle moving perpendicular through a magnetic field experiences a magnetic force perpendicular to both the magnetic field and its velocity. B. Earth's magnetic field attracts the charged particles that make up cosmic radiation. C. A current-carrying wire will also experience a magnetic force perpendicular to both the velocity and the magnetic field. D. Electric motors use current and a magnet to spin an armature by the magnetic force. E. None of these.
B is false. The correct way to say it is: Earth's magnetic field detracts charged particles that make up cosmic radiation,
Which of the following is false? A. If a neutral atom loses electrons, it becomes positively charged. B. If two oppositely charged particles are brought closer together so that the distance between them halves, then the force between them will be multiplied by 1/4. C. An electrically polarized object typically does not have a net charge-the charges are just rearranged in the object. D. A neutral atom becomes an ion through the transfer of electrons. E. None of these.
B is false. The correct way to word this would be: If two oppositely charged particles are brought closer together so that the distance between them halves, then the force between them will be multiplied by 2.
Which of the following is false? A. Current produces a magnetic field, which makes a pattern of concentric circles around the current-carrying wire. B. If a current-carrying wire is bent in a loop, the intensity of the magnetic field inside the loop decreases; using many loops can minimize the magnetic field in the center. C. Superconductors expel magnetic fields, preventing them from penetrating their surface. D. None of these.
B is false. If you multiply the loops in the wire, the intensity of the magnetic field is greatly increased. Not decreased.
Which of the following is false? A. A transformer transfers electrical power from one coil of wire to another using electromagnetic induction. B. If a transformer is used to step-up voltage, the current is increased proportionally. C. An electric field is induced in any region of space in which a magnetic field is changing with time. D. A magnetic field is induced in any region of space in which an electric field is changing with time. E. None of these.
B. If a transformer is used to step-up voltage, the current is increased proportionally.
How could a lightbulb near, but not touching, an electromagnet be lit? A. It cannot be lit. B. It could be lit if it were connected to a loop of wire near the electromagnet and the electromagnet is powered with ac. C. It could be lit if it were connected to a loop of wire near the electromagnet and the electromagnet is powered with dc. D. None of these.
B. It could be lit if it were connected to a loop of wire near the electromagnet and the electromagnet is powered with ac.
A car's headlight dissipates 40 W on low beam and 50W on high beam. Is there more or less resistance in the high beam filament? A. More resistance because as resistance increases, power increases. B. Less resistance because as resistance decreases, current increases. C. The same resistance, because they both are connected to the same 12 V battery.
B. Less resistance because as resistance decreases, current increases.
In a series circuit with a 2 Ohm and a 4 Ohm light bulb, if the current through the 2 Ohm light bulb is 2 A, which of the following is true? A. The current through the 4 Ohm light bulb is greater than 2 A. B. The current through the 4 Ohm light bulb is equal to 2 A. C. The current through the 4 Ohm light bulb is less than 2 A.
B. The current through the 4 Ohm light bulb is equal to 2 A in a series circuit.
In a parallel circuit with a 2 Ohm and a 4 Ohm light bulb, if the voltage drop across the 2 Ohm light bulb is 6 V, which of the following is true? A. The voltage drop across the 4 Ohm light bulb is greater than 6 V. B. The voltage drop across the 4 Ohm light bulb is equal to 6 V. C. The voltage drop across the 4 Ohm light bulb is less than 6 V.
B. The voltage drop across the 4 Ohm light bulb is equal to 6 V.
In what direction do compressed regions and rarefied regions of a longitudinal wave travel?
Both compressions and rarefaction travel parallel to a longitudinal wave.
Which of the following is false? A. In a parallel circuit, each device connects to the same two points, so the voltage across each device is the same. B. In a parallel circuit, the total current divides among each path. C. In a parallel circuit, the current through a given branch is directly proportional to its resistance. D. As the number of branches increases in a parallel circuit, the total resistance decreases and the total current increases. E. none of these.
C is false.
Which of the following is false? A. Direct current flows in one direction. B. In order for electric charge to flow, there must be a different in electric potential. C. A voltage source supplies all of the electrons that flow in the circuit. D. Curent is the flow of electrons.
C is false. A voltage source supplies all of the electron ENERGY that flows in the circuit.
Which of the following is false? A. The unit of charge is the Coulomb (C). B. If the distance between two charges doubles, the force between them is quartered (one-fourth) C. Two electrons can have a different charge. D. Charge is conserved.
C is false. All electrons have the same relative charge.
Which of the following is false? A. Electric potential energy is possessed by a charged particle due to its location. B. Electric potential takes into account the electric potential energy per charge. C. Voltage and electric potential energy are the same thing. D. The unit of electric potential is the volt; 1 volt is equal to 1 joule/coulomb of charge.
C is false. Voltage is the same as electric potential.
Which of the following is false? A. In a vacuum, all electromagnetic waves move at the same speed. B. As the frequency of an electromagnetic wave increases, its wavelength decreases. C. Infrared radiation has a higher frequency than X Ray.s E. None of these.
C is false. X Rays have a higher frequency than Infrared radiation.
Which of the following is false? A. The doppler effect is the change in frequency of a wave due to motion of the source or receiver. B. An increase in light frequency is called a blueshift; a decrease in light frequency is called a redshift. C. For a redshift to occur, the light source must be approaching the receiver. D. The Doppler effect holds for all types of waves. E. None of these.
C is false. For a redshift to occur, the light source must be moving AWAY from the receiver.
Which of the following is false? A. Vibrating electrons emit most electromagnetic waves. B. Glass absorbs ultraviolet light because the electrons vibrating at the frequency of ultraviolet light transfer their energy to neighboring atoms as thermal energy. C. Glass is transparent to visible light; visible light will pass through glass without being absorbed by electrons. D. None of these.
C is false. Glass is transparent to visible light. Visible light will pass through glass by being absorbed by electrons then re-emitted through.
Which of the following is false? A. As period increases, frequency decreases. B. Energy is what moves from source to receiver in wave motion. C. The medium through which a wave travels will move from source of the wave to the receiver. D. None of these.
C is false. Only energy moves, not the medium.
Which of the following is false? A. Like poles of a magnet repel; opposite poles of a magnet attract. B. If you break a magnet in half, each half will behave as a complete magnet. C. Magnetic poles can be isolated just like electric charges, so a magnet can have just a north pole or just a south pole. D. None of these.
C is false. The correct way to word this would be: Magnetic poles cannot be isolated. Each magnet has a north and a south pole.
All bulbs are identical in the three circuits. An ammeter is connected next to each battery as shown. Rank the current readings in the ammeter from highest to lowest.
C, B, A
Which of the following is false? A. A charge moving parallel to an external magnetic field experience a minimum deflecting force, but a charge moving perpendicular experience a maximum force. B. Two oppositely charged particles will be deflected on opposite direction when moving in the same direction perpendicular to a magnetic field. C. A pair of current-carrying wires will not exert forces on each other because their magnetic fields are parallel. D. None of these.
C. A pair of current-carrying wires will not exert forces on each other because their magnetic fields are parallel.
Which of the following is false? A. The transmission of sound requires a medium. B. Solids and liquids are generally better conductors of sound than air. C. All sound travels at the same speed in a given medium, but speed of sound does depend on volume. D. Pitch is subjective impression of the frequency of sound. E. None of these.
C. All sound travels at the same speed in a given medium is true. The rest is false.
To make a compass, point an ordinary iron nail along the direction of Earth's magnetic field and repeatedly strike it for a few seconds with a hammer or rock. Then suspect it at its center of gravity by a string. Why does the act of striking magnetize the nail? A. Striking adds electrons to the nail (electrons are magnetic). B. Striking removes electrons from the nail so that more electrons are unpaired. C. Striking shakes up the domains, allowing them to align with the external magnetic field. D. None of these.
C. Striking shakes up the domains, allowing them to align with the external magnetic field.
In a parallel circuit with a 2 Ohm and a 4 Ohm light bulb, if the current through the 2 Ohm light bulb is 2 A, which of the following is true? A. The current through the 4 Ohm light bulb is greater than 2A. B. The current through the 4 Ohm light bulb is equal to 2 A. C. The current through the 4 Ohm light bulb is less than 2 A.
C. The current through the 4 Ohm light bulb is less than 2 A.
How does an electrically polarized object differ from an electrically charged object?
Charge in a polarized object is simply re-arranged, with a net force normally zero. A charged object has a non-zero net charge.
Tiny particles, like tiny bells, scatter high-frequency waves more than low-frequency waves. Large particles, like large bells, mostly scatter low frequencies. Intermediate-size particles and bells mostly scatter intermediate frequencies. What does this have to do with the whiteness of clouds?
Clouds are composed of atoms, molecules, and particles of a variety of sizes. So not only are high- frequency colors scattered from clouds, but middle and low frequencies as well. A combination of all the scattered colors produces white.
Which of the following is false? A. Positively charged atoms have lost one or more electrons. B. Like charges repel; opposite charges attract. C. Protons are positively charged, electrons are negatively charged, and neutrons are neutral. D. If an object becomes polarized, it transfers electrons to another object.
D is false.
Which of the following is false? A. In order for electric charge to flow, there must be a difference in electric potential. B. The flow of electrical charge is called current; it is measured in amperes (coulomb of charge per second) C. A voltage source supplies a continuous difference in electric potential by separating opposite charges. D. A voltage source contains all of the electrons that flow in the circuit. E. Direct current flow in one direction. F. None of these.
D is false.
Which of the following is false? A. A battery produces dc in a current. B. According to Ohm's law, for a given voltage, as resistance increases, current decreases. C. According to Ohm's law, for a given current, as resistance increases, the voltage (drop) increases. D. When connected to the same voltage, a lamp with a thinner filament will draw more current than a lamp with a thicker filament.
D is false. A thinner wire has more resistance than a thicker wire. Therefore, a thicker wire will draw more current in the same voltage than a thinner wire.
Which of the following is false? A. Different frequencies of light travel at different speeds through a transparent medium. B. The separation of light by its frequencies when passing through a medium is called dispersion. C. Rainbows are created by dispersion of light in drops of water. D. You can see a rainbow from the side (end-on) if you circle around it. E. None of these.
D is false. You see the rainbow from between 40 and 42 degrees on. You can't see it from the side.
Which of of the following is false? A. According to Ohm's law, if voltage increases, current increases. B. According to Ohm's law, if resistance increases, current decreases. C. A person could hang from na electrical wire with high potential and not get shocked. D. If an electrical wire with high potential was hanging low to the ground, a tall person could reach up and grab it as he is walking by and not get shocked. E. None of these.
D is false. NO!!! Don't ever walk by an electrical wire and touch it while your feet or any part of your body is touching something else.
Which of the following is false? A. Current can be produced in a coil of wire by moving a magnet into or out of the coil. B. Voltage is induced by the relative motion between a wire (a conductor) and a magnetic field. C. Pushing a magnet into a coil with twice as many loops produces twice the voltage. D. The more loops in a coil of wire, the easier it is to push a magnet through the coils. E. None of these.
D is false. The more coils, the harder it is to push through.
Which of the following is false? A. The refraction of light is due to different speeds in different mediums. B. Due to refraction, a submerged object appears to be closer to the surface than it actually is. C. Because of refraction, when the sun is near the horizon it appears to be higher in the sky. D. A mirage is when reflected light appears as if it were refracted light. E. None of these.
D is false. A mirage is when REFRACTED light appears as if it were REFLECTED light.
Which of the following is false? A. Electric fields extend out from charged particles similar to gravitational fields extending out from mass. B. The electric field stores energy. C. A charged particle can interact with the electric field of another charged particle, causing a force. D. Electric fields of like charged are attracted to each other; electric fields of oppositely charged particles repel one another. E. None of these.
D is false. The correct way to say D would be: Electric fields of like charges repel one another; electric fields of oppositely charged particles attract.
Which of the following is false? A. The direction of an electric field is defined in terms of the direction of force on a positive charge. B. Two common force fields are gravitational and electric force fields. C. The strength of a force field decreases proportionally to the square of the distance to the charge. D. An object can have a large electric potential, but a small voltage. E. Electric potential energy is the energy a charge possesses due to its location in an electric field. F. None of these.
D is false. Electric potential and voltage are the same thing. You cannot have a large amount of one and a small amount of the other.
Which of the following is false? A. Waves on the surface of liquids are transverse waves. B. A longitudinal wave is one in which the direction of wave travel is along the direction in which the source vibrates. C. A rarefraction is the portion of a longitudinal wave between successive compressions. D. Electromagnetic waves and sound waves are longitudinal waves. E. None of these.
D. Electromagnetic waves are transverse waves. Sounds waves are longitudinal.
Which of the following is false? A. IN order to sustain the flow of electric charge through a conducting medium, a difference in electric potential must be maintained. B. 12 joules of energy are given to each coulomb of charge passing through a 12 V battery. C. DC moves in one direction; a battery produces DC in a circuit. D. None of these.
D. None of these
Which of the following is false? A. Light from the sun is normally unpolarized, so it has electromagnetic waves vibrated at all angles. B. Plane-polarized light has electromagnetic waves vibrating in a single plane. C. The light reflected from nonmetallic surfaces is polarized. D. None of these.
D. None of these.
Which of the following is false? A. A generator cannot produce energy, only transfer it from one form to another. B. A transformer can change voltage and current, but not energy or power. C. An electric field is induced by the rapid alternation of a magnetic field. D. None of these.
D. None of these.
Which of the following is false? A. A generator converts mechanical energy into electrical energy; a motor converts electrical energy into mechanical energy. B. The current produced by a generator is AC. C. Generators don't produce energy; they can only convert it from one form to another. D. None of these.
D. None of these.
Which of the following is false? A. If the speed of a wave is constant, then as frequency increases, wavelength decreases. B. In a transverse wave, the vibrations are perpendicular to the wave motion; in a longitudinal wave, the vibrations are parallel to wave motion. C. Sound travels faster in water than in air, but even faster in steel. D. None of these.
D. None of these.
Which of the following is false? A. If you break a magnet in half, each half will behave as a complete magnet. B. Like poles of a magnet repel; opposite poles of a magnet attract. C. Magnetic poles cannot be isolated like electric charges. A magnet cannot have just a north pole or just a south pole. D. None of these.
D. None of these.
Which of the following is false? A. In a series circuit, current has one pathway so the same current flows through each electrical device. B. The total resistance in a series circuit is the sum of the individual resistances along the currents path. C. The device with the largest resistance will have the largest voltage drop in a series circuit. D. None of these.
D. None of these.
Which of the following is false? A. Magnetic materials have atoms with unpaired electrons. B. A magnetic domain is a cluster of magnetic atoms that are all aligned. C. The domains are normally not aligned in a material, but an external magnetic field can force them to align; this process induces a magnetic field. D. None of these.
D. None of these.
Which of the following is false? A. The attraction between two oppositely charged particles is inversely proportional to the square of the distance between the particles. B. If the charge of one or two oppositely charged particles doubles, the force between them will double. C. The unit of charge is the coulomb (C). D. When an object becomes polarized, it transfers electrons to a different object. E. None of these.
D. When an object becomes polarized, it transfers electrons to a different object. -This is false.
How do dolphins perceive their environment in dark and murky water?
Dolphins perceive their environment by the ultrasound they emit and the timing of its echoes.
During a lunar eclipse, the moon is not completely dark, but is often deep red. Explain this in term of the refraction of all the sunsets and sunrises around the world.
During a lunar eclipse the Moon is not totally dark, even though it is in Earth's shadow. This is because the atmosphere of Earth acts as a converging lens that refracts light into Earth's shadow. It is the low frequencies that pass more easily through the long grazing path through Earth's atmosphere to be refracted finally onto the Moon. Hence its reddish color—the refraction of the whole world's sunups and sunsets.
Which of the following is false? A. A yellow page will look green in green light. B. A yellow page will look black in green light. C. Mixing magenta and green pigments will produce black. D. Mixing magenta and green lights will produce white light. . E. A magenta page will look white in green light. F. None of these.
E is false.
Which of the following is false? A. According to the law of reflection, the angle of incidence equals the angle of reflection. B. When light strikes the pages of your textbook, it undergoes diffuse reflection. C. The black ink in your textbook absorbs all the visible frequencies of light. D. A flat mirror is called a plane mirror; a convex mirror curves outward. E. None of these.
E. None of these
Which of the following is false? A. A proton is positively charged; an electron is negatively charged. B. The charge of every electron is the same. C. In a neutral atom, the number of electrons and protons are equal. D. Charge cannot be created or destroyed--only transferred. E. None of these.
E. None of these.
Which of the following is false? A. All magnetic fields are produced by the motion of electric charge. B. Electrons are in constant motion. C. Every spinning electron produces a magnetic field. D. In atoms, the effect of one electron's magnetic field can be canceled by another electron whose spin is in the opposite direction. E. None of these.
E. None of these.
Which of the following is false? A. Different frequencies of light are perceived as different colors. B. White light from the sun is a composite of all visible frequencies. C. Red ink on a page looks red because it reflects red light. D. An object can only reflect frequencies present in the illuminating light, so a blue object will not look blue in red light. E. None of these.
E. None of these.
Which of the following is false? A. The amplitude of a wave is the distance from the mid point of the wave to the crest. B. The distance between two successive crests of a wave is its wavelength. C. The frequency of a wave is the number of crests that pass by a particular point per unit time. D. The source of any wave is something that vibrates. E. None of these.
E. None of these.
Which of the following is false? A. The vibration of a factory floor caused by the running of heavy machinery is an example of forced vibration. B. When a tuning fork is struck, it vibrates at its natural frequency. C. A bridge can have a natural frequency and undergo resonance. D. Both longitudinal and transverse waves can undergo constructive or destructive interference. E. None of these.
E. None of these.
Which of the following is false? A. a magnetic domain is a region of aligned magnetic atoms (like iron). B. The magnetic field about a current-carrying wire takes the shape of concentric circles. C. If the direction of current is reversed in a current-carrying wire, the magnetic field direction is also reversed. D. The magnetic field inside a current-carrying loop of wire is greater than the field strength about a straight section of wire. E. None of these.
E. None of these.
Which of the following is false? A. Electric potential energy possessed by a charged particle due to its location. B. Electric potential (voltage) takes into account the electric potential energy per charge. C. An object can have a high voltage, but a low electric potential energy if there is only a small amount of charge. D. The unit of electric potential is the volt; 1 volt is equal to 1 Joule/coulomb of charge. E. None of these.
E. None of these. They are all true.
Which of the following is false? A. Like charges repel; opposite charges attract. B. Protons are positively charged, electrons are negatively charged, and neutrons are neutral. C. Positively charged atoms have lost one or more electrons; negatively charged atoms have gained on or more elections. D. Charge is conserved. E. None of these.
E. None of these. They are all true.
What effect does Earth's magnetic field have on the intensity of cosmic rays striking Earths surface?
Earth's magnetic field deflects many of the incoming cosmic rays, reducing the intensity of rays reaching Earth's surface.
Distinguish between electric potential energy and electric potential in terms of units of measurement.
Electric potential energy is measured in joules; electric potential is measured in volts.
Why is charge usually transferred by electrons rather than by protons?
Electrons are loosely bound on the outside of atoms, whereas protons are very tightly bound within the atomic nuclei.
Does more current "flow" out of a battery than into it? Does more current "flow" into a lightbulb than out of it?
Electrons flow through electrical devices, just as water flows through a plumbing circuit of pipes. If a water pump produces water pressure, water flows through both the pump and the circuit. Likewise with electric current in an electric circuit. For example, in a simple circuit consisting of a battery and a lamp, the electric current in the lamp is the same electric current through the wires that connect the lamp and the same electric current through the battery. Current "flows" through these devices. (As a side point, it is common to speak of electric current flowing in a circuit, but it is electric charge that flows in an electric circuit; the flow of charge is current. So if you want to be grammatically correct, say that current is in a circuit and charge flows in a circuit.)
How could you use the spotlights at a play to make the yellow clothes of the performers suddenly change to black?
If the yellow clothes of performers are illuminated with a complementary blue light, they will appear black.
What is absorbed by water to give it a cyan color?
Infrared and red light are absorbed by water. Absorption of red produces the complementary color, cyan.
In a mass spectrometer, ions are directed into magnetic field, where they curve around in the field and strike a detector. If a variety of singly ionized atoms travel at the same speed through the magnetic field, would you expect them all to be deflected by the same amount? Or would you expect different ions to be bent by different amounts?
Singly-charged ions traveling with the same speed through the same magnetic field will experience the same magnetic force. The extent of their deflections will then depend on their accelerations, which in turn depend on their respective masses. The least massive ions will be deflected the most and the most massive ions will be deflected the least.
Does sound travel faster in warm air or in cold air?
Sound travels faster in warm air because the air molecules that compose warm air themselves travel faster and therefore don't take as long before they bump into each other. Hence a lesser time for the molecules to bump against one another that results in a faster speed of sound.
If you fire a bullet through a board, it will slow down inside and emerge at a speed that is less than the speed at which it entered. Does light, then, similarly slow does when it passes through glass and also emerge at a lower speed?
The instantaneous speed of the bullet after penetrating the board is less than its incident speed, but not so with light. The instantaneous speed of light before meeting the glass, while passing through it, and when emerging is a constant, c. The fundamental difference between a bullet fired through a board and light passing through glass is that in the case of the bullet, the same bullet strikes and later emerges. Not so for light. The "bullet of light" (photon) that is incident upon glass is absorbed by its interaction with an atom or molecule. The atom or molecule in turn then emits, with some time delay, a new "bul- let of light" in the same direction. This process cascades through the glass with the result being that the "bullet of light" emerging is not the same "bullet" that was first incident. In the space between the atoms in matter the instantaneous speed of light is c. Because of the time delay of the interactions, only its average speed is less than c. The light that emerges has speed c.
A magnetic field can deflect a beam of electrons, but it cannot do work on the electrons to change their speed.
When we write work=force x distance, we really mean the component of force in the direction of motion multiplied by the distance moved (Chapter 3). Since the magnetic force that acts on a beam of electrons is always perpendicular to the beam, there is no component of magnetic force along the instantaneous direction of motion. Therefore a magnetic field can do no work on a charged particle. (Indirectly, however, a time-varying magnetic field can induce an electric field that can do work on a charged particle.)
