Physics Final Exam Chapters 24-27

25 July 2022
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question
By whom and in what setting, was the relationship between electricity and magnetism discovered?
answer
Hans Christian Oersted discovered the relationship between electricity and magnetism in a classroom setting.
question
The force between electrically charged particles depends on the magnitude of each charge, their separation distance, and what else?
answer
The force between electrically charged particles also relies on the motion of the particles.
question
What is the source of magnetic force?
answer
The source of magnetic force is the motion of charged particles, usually electrons.
question
Is the rule for the interaction between magnetic poles similar to the rule for the interaction between electrically charged particles?
answer
Yes, because both can repel and attract without touching depending on which ends of the magnets are held near one another.
question
In what way are magnetic poles very different from electric charges?
answer
Magnetic poles cannot be isolated but electric charges can.
question
How does magnetic field strength relate to the closeness of magnetic field lines about a bar magnet?
answer
The closer the magnetic field lines, the stronger the field.
question
What produces a magnetic field?
answer
The motion of electric charges produces a magnetic field.
question
What two kinds of rotational motion do electrons in an atom appear to have?
answer
Electron revolution and electron spin
question
What is a magnetic domain?
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A magnetic domain is a cluster of aligned atoms.
question
At the micro level, what is the difference between an unmagnetized iron nail and a magnetized iron nail?
answer
Thermal energy.
question
Why is iron magnetic and wood is not?
answer
Iron has magnetic domains, wood does not.
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Why will dropping an iron magnet on a concrete sidewalk make it a weaker magnet?
answer
Dropping the iron magnet will knock the domains out of alignment and weaken the magnet.
question
In Chapter 22, we learned that the direction of the electric field about a point charge is radial to the charge. What is the direction of the magnetic field surrounding a current-carrying wire?
answer
The magnetic field takes the form of concentric circles around the current-carrying wire.
question
What happens to the direction of the magnetic field about an electric current when the direction of the current is reversed?
answer
When the current is reversed, the direction of the compass needle turns around to show that the magnetic field is reversed.
question
Why is the magnetic field strength greater inside a current-carrying loop of wire than about a straight section of wire?
answer
Inside the loops, the lines are more concentrated.
question
Why does a piece of iron in a current-carrying loop increase the magnetic field strength?
answer
Magnetic domains in the iron are induced into alignment, which add to the magnetic field strength.
question
Why are the magnetic fields of superconducting magnets often stronger than those of conventional magnets?
answer
Greater electron flow produces greater magnetic field strength.
question
True or false: A charged particle must move in a stationary magnetic field in order that a force due to the field act on.
answer
...
question
In what direction relative to a magnetic field does a charged particle move in order to experience maximum deflecting force? Minimum deflecting force?
answer
Force is maximum when perpendicular to the field and is minimum when parallel to the field.
question
What effect does Earth's magnetic field have on the intensity of cosmic rays striking Earth's surface?
answer
Earth's magnetic field deflects cosmic rays from striking Earth's surface.
question
What relative direction between a magnetic field and a current-carrying wire results in the greatest force?
answer
Force is maximum when the current is perpendicular to the field.
question
How does a galvanometer detect electric current?
answer
Galvanometers detect electric current through movement.
question
What is a galvanometer called when it has been calibrated to read current? What it has been calibrated to read voltage?
answer
When set to read current it is call an ammeter and when set to read voltage, it is a voltmeter.
question
How often is current reversed in the loops of an electric motor?
answer
The current is reversed every half-rotation.
question
Is it correct to say that an electric motor extends the physics that underlies a galvanometer?
answer
Yes, a motor is a sophisticated galvanometer.
question
Why are there probably no permanently aligned magnetic domains in Earth's core?
answer
Because it is too hot in Earth's core for atoms to hold to a proper orientation.
question
What are magnetic pole reversals?
answer
Magnetic pole reversals are reversals of the north and south poles.
question
What is the cause of the aurora borealis (northern lights)?
answer
The cause is charged particles in the Van Allen belt striking atmospheric molecules.
question
Name at least six creature that are known to harbor tiny magnets within their bodies.
answer
Bacteria, pigeons, bees, Monarch butterflies, sea trutles, and fish.
question
When do cosmic rays penetrate your body?
answer
All the time.
question
What important discovery did physicists Michael Faraday and Joseph Henry make?
answer
They discovered that electric current can be produced in a wire simply by moving a magnet in or out of loops, or electromagnetic induction.
question
What must change in order for electromagnetic induction to occur in a wire coil?
answer
The magnetic field in the coil of wire.
question
State Faraday's law.
answer
The induced voltage in a coil is proportional to the product of its number of loops, the cross-sectional area of each loop, and the rate at which the magnetic field changes within those loops.
question
What are the three ways in which voltage can be induced in a loop of wire?
answer
By moving the loop near a magnet, by moving the magnet near a loop, and by changing a current in a nearby loop.
question
How does the frequency of induced voltage relate to how frequently a magnet is plunged in and out of a coil of wire?
answer
Both frequencies are the same.
question
What are the basic differences and similarities between a generator and an electric motor?
answer
They both transform energy, but their input and outputs are different. The input of a motor is electric energy and the output is mechanical energy. In a generator mechanical energy is the input and electric energy is the output.
question
Is the current that is produced by a common generator ac or dc?
answer
Generators produce alternating currents.
question
What is the common frequency of ac in homes in the United States?
answer
60 Hz.
question
Who discovered electromagnetic induction, and who put it to practical use?
answer
Michael Faraday and Joseph Henry discovered electromagnetic induction, but Nikola Tesla and George Westinghouse put it to use.
question
What is an armature?
answer
An armature is an iron core wrapped with bundles of copper wire.
question
What commonly supplies the energy input to a turbine?
answer
Steam supplies energy to a turbine.
question
Is it correct to say that a generator produces energy? Defend your answer.
answer
Generators do not produce energy, they simply convert energy from one source to another.
question
What are the principal differences between an MHD generator and a conventional generator?
answer
MHD generators have no moving parts.
question
Does an MHD generator employ Faraday's law of induction? Explain.
answer
No. There are no changing magnetic fields in an MHD generator.
question
What name is given to the rate at which energy is transferred?
answer
Power is the rate at which energy is transferred.
question
Is it correct to say that a transformer boosts electric energy? Defend your answer.
answer
If it is a step up transformer, then yes. If the secondary coils have more loops than the primary coil then the voltage will be increased. If the secondary coils have fewer loops, then the voltage produced will be decreased (a step down transformer).
question
Which of these does a transformer change: voltage, current, energy, power?
answer
A transformer changes voltage and current, but it does not change energy or power.
question
How does the power input to an efficient transformer compare with the power output?
answer
If they have the same number of wires, then the input and output will be equal.
question
What exactly does a step-down transformer step down?
answer
Step-down transformers step down voltage.
question
In a step-down transformer, how does the input current compare with the output current?
answer
The input will equal the output in a step-down transformer.
question
Why does a transformer require ac?
answer
Transformers require alternating currents because they operate depending on change.
question
What is the principal advantage of ac over dc?
answer
Transformers require alternating currents because they are easier to step-up or step-down.
question
When the magnetic field changes in a coil of wire, voltage in each loop of the coil is induced. Will voltage be induced in a loop if the source of the magnetic field is the coil itself?
answer
Yes, this is known as self-induction.
question
What is the purpose of transmitting power at high voltages over long distances?
answer
This is done for long distance transmission.
question
Does the transmission of electric energy require electric conductors between the source and receiver? Cite an example to defend your answer.
answer
No wires are needed. Personal electronic devices attest to this.
question
Who extended Faraday's law to changing electric fields?
answer
James Clerk Maxwell.
question
What is induced by the rapid alternation of a magnetic field?
answer
An alternating electric field is induced.
question
What is induced by the rapid alternation of an electric field?
answer
A magnetic field is induced by the rapid alternations of electric fields.
question
Are wires needed in Maxwell's view of Faraday's law?
answer
No, no wires are needed.
question
What do we call electromagnetic waves in the range of frequencies that match what our eyes can see?
answer
Electromagnetic waves that match our eyes are light.
question
What does a changing magnetic field induce?
answer
A changing magnetic field induces an electric field.
question
What does a changing electric field induce?
answer
A changing electric field induces a magnetic field.
question
What produces an electromagnetic wave?
answer
An electromagnetic wave is produced by vibrating electric and magnetic fields.
question
How is the fact that an electromagnetic wave in space never slows down consistent with the conversation of energy?
answer
If an electromagnetic wave were to slow down, its changing electric field would generate a weaker magnetic field, which would generate a weaker electric field and so on until the wave died out. This would cause a loss of energy and nothing would be transported.
question
How is the fact that an electromagnetic wave in space never speeds up consistent with the conservation of energy?
answer
If an electromagnetic wave were to increase, the electric field would generate a stronger magnetic field, which would generate a stronger electric field and so on which would require increasing energy.
question
What do electric and magnetic fields contain and transport?
answer
Electric and magnetic fields contain and transport light.
question
What is the principal difference between a radio wave and light? Between light and an X-ray?
answer
The principal difference between radio waves, light waves, and X-rays is frequencies.
question
About how much of the measured electromagnetic spectrum does light occupy?
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Visible light makes up less than 1% of the electromagnetic spectrum.
question
What is the color of visible light of the lowest frequencies? Of the highest frequencies?
answer
The color of visible light at the lowest frequency appears to be red and the highest frequency appears to be violet.
question
How does the frequency of a radio wave compare to the frequency of the vibrating electrons that produce it?
answer
The frequency of a radio wave is the same as the frequency of the vibrating electrons that produced it.
question
How is the wavelength of light related to its frequency?
answer
Higher frequencies of light have shorter wavelengths.
question
What is the wavelength of a wave that has a frequency of 1 Hz and travels at 300,000 km/s?
answer
300,000 km.
question
What do we mean when we say that outer space is not really empty?
answer
Outer space is filled with electromagnetic waves.
question
The sound coming from one tuning fork can force another tuning for to vibrate. What is the analogous effect for light?
answer
A sound coming from one tuning fork to another is analogous to the effect of light traveling through a transparent material.
question
In what region of the electromagnetic spectrum is the resonant frequency of electrons in glass?
answer
The resonant frequency of glass is in the ultraviolet region.
question
What is the fate of the energy in ultraviolet light that is incident upon glass?
answer
Glass isn't transparent to ultraviolet light, so these lights collide with neighboring atoms and give up its energy as heat.
question
What is the fate of the energy in visible light that is incident on glass?
answer
The visible light energy is re-emitted as light from the other side of the glass.
question
What is the fate of the energy in infrared light that is incident on glass?
answer
The energy in infrared waves increase the internal energy and temperature of the structure, which is why they are also called heat waves.
question
How does the frequency of re-emitted light in a transparent material compare with the frequency of the light that stimulates its re-emission?
answer
The frequencies are the same.
question
How does the average speed of light in glass compare with its speed in a vacuum?
answer
The average speed of light in glass is .67 c and the average speed of light in a vacuum is 300,000 km/s.
question
How does the speed of light that emerges from a pane of glass compare with the speed of light incident on the glass?
answer
The incident and emerging speed of light are the same.
question
Why are infrared waves often called heat waves?
answer
Infrared waves are often called heat waves because they increase the internal energy and temperatures of structures.
question
Why do opaque materials become warmer when light shines on them?
answer
Opaque materials absorb the energy and transform it to thermal energy.
question
Why are metals shiny?
answer
Metals are shiny because the electrons do not spring from atom to atom but instead reflect the light shone on the metal.
question
Why do wet objects normally look darker than the same objects when dry?
answer
Multiple reflections absorb light, and the light emerging is weaker.
question
Distinguish between an umbra and a penumbra.
answer
An umbra is the darker part of the shadow where all the light is blocked. A penumbra is a partial shadow that appears where some but not all of the light is blocked.
question
Do Earth and the Moon always cast shadows? What do we call the occurrence where one passes within the shadow of the other?
answer
The Earth and Moon cast shadows when light is upon them. We call these eclipses.
question
How do the rods in the eye differ from the cones?
answer
The rods handle vision in low light and the cones handle color vision.
question
When are objects on the periphery of your vision most noticeable?
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Objects in the periphery are best seen when they're in motion.
question
What besides the amount of light affects the size of the pupil of the eye?
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Attraction and repulsion cause the pupils to grow or decrease in size.
question
Which has the higher frequency: red light or blue light?
answer
Blue light has the higher frequency.
question
What occurs when the outer electrons that buzz about the atomic nucleus encounter electromagnetic waves?
answer
They can be forced into vibration by the electric fields of the electromagnetic waves.
question
What happens to light when it falls on a material that has a natural frequency of the light?
answer
When light falls on a material with matching natural frequency, it is absorbed.
question
What happens to light when it falls on a material that has a natural frequency above or below the frequency of the light?
answer
The light is re-emitted.
question
What color light is transmitted through a piece of red glass?
answer
Red light is transmitted through red glass.
question
How does a pigment affect light?
answer
Pigments are particles that selectively absorb lights of certain frequencies and transmits others.
question
Which warms more quickly in sunlight: a colorless or a colored piece of glass? Why?
answer
A colored piece of glass will warm more quickly because it absorbs lights.
question
What is the evidence for the statement that white light is a composite of all the colors of the spectrum?
answer
The evidence is that of which Newton provided us with; he placed a prism that reflected a rainbow colored spectrum and when he placed a second prism, the rainbow color turned to a white spectrum.
question
What is the color of the peak frequency of solar radiation?
answer
The peak frequency of solar radiation is yellow-green.
question
To what color of light are our eyes most sensitive?
answer
The yellow-green range.
question
What is a radiation curve?
answer
A radiation curve is the graphical distribution of brightness versus frequency
question
What frequency ranges of the radiation curve do red, green, and blue light occupy?
answer
Lower frequencies appear to be red, middle frequencies appear to be green, and high frequencies appear to be blue.
question
Why are red, green, and blue called the additive primary colors?
answer
When they are added together they can produce any color in the spectrum.
question
What is the resulting color of equal intensities of red light and cyan light combined?
answer
Red and cyan light combined make white.
question
Why are red and cyan called complementary colors?
answer
Because when they are added together, they produce white.
question
When something is painted red, what color is most absorbed?
answer
The color most absorbed is cyan.
question
What are the subtractive primary colors?
answer
The subtractive colors are cyan, yellow and magenta.
question
If you look with a magnifying glass at pictures in a book or magazine that are printed in full color, you'll notice three colors of ink plus black. What are these colors?
answer
Cyan, magenta, yellow and black.
question
Which interact more with high-pitched sounds: small bells or large bells?
answer
Small bells interact more with high frequency sounds.
question
Which interact more with high-frequency light: small particles or large particles?
answer
The small particles interact more with high frequency sounds.
question
Why does the sky normally appear blue?
answer
The sky normally appears blue because the blue end of the spectrum is scattered more.
question
Why does the sky sometimes appear whitish?
answer
The sky will appear whitish if the atmosphere contains a lot of dust particles and other particles larger than oxygen and nitrogen molecules.
question
Why does the Sun look reddish at sunrise and sunset but not at noon?
answer
Scattering of high frequency blue light occurs all along the path of sunlight, so the long path at sunrise or sunsets finds much blue missing. The remaining light is that of lower frequencies which account for the reddish color of the sun at these times.
question
Why does the color of sunsets vary from day to day?
answer
The combinations of the sunset colors vary with atmospheric conditions which change from day to day.
question
Is it scattering or reflection that accounts for the whiteness of a cloud?
answer
A cloud is white because it reflects all the colors of the spectrum equally.
question
What is the effect on the color of a cloud when it contains an abundance of large droplets?
answer
If you have a cloud with several large droplets, the cloud will appear gray because the droplets are absorbing the colors.
question
What part of the electromagnetic spectrum is most absorbed by water?
answer
Infrared light is most absorbed by water.
question
What part of the visible electromagnetic spectrum is most absorbed by water?
answer
Infrared light is most absorbed by water.
question
What color results when red is subtracted from white light?
answer
When red is subtracted from white light, the result is cyan.
question
Why does water appear cyan?
answer
Because water reflects the sky.