# Physics Final Exam Chapters 24-27

## Unlock all answers in this set

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