Physics - Exam 4 Review (Ch.15-17, 19)
You wish to warm 45 kg of water by 20∘C for your bath. Select the correct equation that shows that this is equivalent to about 3800 kJ.
(900kcal)(4.19kJ/kcal)=3771kJ
From greatest to least, rank the wires in how much they'll sag on a hot summer day. A: Copper, α=17×10−6/∘C B: Aluminum, α=24×10−6/∘C C: Steel, α=11×10−6/∘C
B,A,C
Rank the magnitudes of the following units of thermal energy from greatest to least: A: 1 calorie B: 1 Calorie C: 1 joule
B,A,C
What happens to conductive properties of wood when it get very hot?
It will continue to remain a good insulator.
What happens to water at room temperature if you decrease the atmospheric pressure around it?
It will first boil and then freeze.
In an insulated vessel, a quantity of hot water at temperature T1 is mixed with a different quantity of cold water at temperature T2. After equilibrium is established, the vessel contains __________.
water only
In an insulated container, 0.800 kg of water at 40.0∘C is mixed with 0.500 kg of ice at −15.0∘C. Find the final temperature Tf of the system. The freezing point of water is 0∘C.
0 ∘C
Which one of these represents the largest amount of energy?
1 Calorie
How many calories are needed to change the temperature of 1 g of water by 1°C? To melt 1 g of ice at 0°C? To vaporize 1 g of boiling water at 100°C?
1 calorie, 80 calories, 540 calories
Which one of these cites the lowest temperature?
270 K
Rank the boiling-water temperatures in different locations. (largest to smallest) A Death Valley B sea level C Denver, CO (the 'mile-high city")
A B C
Distinguish between a calorie and a Calorie
A Calorie is 1000 calories.
Why are icebergs often surrounded by fog?
Air above the freezing temperature is chilled in the vicinity of an iceberg and condensation of the water vapor in the air results in fog.
In a still room, smoke from a candle will sometimes rise only so far, not reaching the ceiling. Explain why.
Air currents depend on convection. In a still room, warm air collects at the top and cool air at the bottom; the air stratifies by temperature (because density depends on temperature). The smoke rises to the point where it has the same density as the air, and stops.
Ethyl alcohol has about one-half the specific heat capacity of water. If equal masses of each at the same temperature are supplied with equal quantities of heat, which will undergo the greater change in temperature?
Alcohol, for less specific heat means less thermal inertia and a greater change in temperature.
In what form does radiant energy travel?
As electromagnetic waves
Your instructor hands you a closed flask partly filled with room-temperature water. When you hold it, the heat transfer between your bare hands and the flask causes the water to boil. Quite impressive! How is this accomplished?
Because it's closed, theirs no air pressure, so you raise the pressure with your touch.
Why does the strip behave as it does when Dr. Hewitt heats it up?
Both metals expand unequally.
Rank the energies needed for different phase changes for equal amounts of H2O. (largest to smallest) A ice to ice water B ice water to boiling water C boiling water to steam
C B A
Rank from greatest to least the volumes of water of the same mass at the following temperatures: A: 0∘C B: 4∘C C: 10∘C
C,A,B
In an insulated container, 0.50 kg of water at 80∘C is mixed with 0.050 kg of ice at −5.0∘C. After a while, all the ice melts, leaving only the water. Find the final temperature Tf of the water. The freezing point of water is 0∘C.
Change in the temperature of cold water dT = Tf-0 C = Tf Change in the temperature of original water in the container dT' = 80-Tf Latent heat of melting of ice L = 80cal/gSpecific heat of water C = 1cal/g C Heat absorbed by ice to melt = mass(mi) x latent heat(L) Heat absorbed by water = mass(mw) x specific heat(C) x change in temperature (dT') mi=0.050kg= 50g and mw=0.50kg = 500g So, heat absorbed by the ice + heat absorbed by cold water = heat lost by hot water( at 80 C) miL + miCdT = mw*CdT'5080 + 501(Tf) = 500 1 * (80-Tf) Cancelling out 50 from each term,80+Tf=800- 10TfSo 11Tf =720 Tf = 65.45 C
Distinguish between weather and climate.
Climate is what you expect, whereas weather is what you get.
What is condensation? Is condensation a warming or cooling process?
Condensation is when a gas becomes a liquid. It is a warming process.
When the temperature of ice-cold water is increased slightly, does it undergo a net expansion or a net contraction?
Contraction
What is the role of "loose" electrons in heat conductors?
Free electrons can move through a material carrying heat, jostling atoms and other electrons.
When can you withdraw heat from something without lowering its temperature?
During a phase change.
If you hold one end of a piece of metal against a piece of ice, the end in your hand soon becomes cold. Does cold flow from the ice to your hand? Explain.
Energy "flows" from higher to lower temperature, from your hand to the ice. It is the energy, heat, flowing from your hand that produces the sensation of coolness. There is no flow from cold to hot; only from hot to cold.
Distinguish between evaporation and boiling.
Evaporation happens at a liquid surface, whereas boiling occurs in the bulk of the liquid.
Each of the following items states a temperature, but does not tell you whether the temperature is measured on the Fahrenheit, Celsius, or Kelvin scale. Match the items to the appropriate temperature scale.
F: a hot summer day 100 ice cream stored in freezer at 26 C: water freezes into ice 0 typical room temperature 24 liquid water boils at 100 K: coldest possible temperature is 0 water into gas phase 373.15
Why is it important that glass mirrors used in astronomical observatories be composed of glass with a low "coefficient of expansion"?
Higher expansion rates mean greater differences in shape with different temperature, which is bad for telescopes.
One of the reasons the first light bulbs were expensive was due to the platinum electrical lead wires into the bulb, necessary because they expanded at about the same rate as glass when heated. Why is it important that the metal leads and the glass have the same coefficient of expansion?
If the coefficients were not the same, then the glass may crack while the wires haven't even heated up enough. When glass cracks, air enters in the figment which will cause oxidization i.e. a failed bulb.
An inventor claims to have developed a new perfume that lasts a long time because it doesn't evaporate. Comment on this claim.
In order to smell something, the molecules must evaporate and reach your nose. If the new perfume doesn't evaporate, it will not have an odor.
Does a good insulator prevent heat from escaping or slow its passage?
Insulators slow the passage of heat.
How does using a pressure cooker affect the amount of internal energy in the water inside the pressure cooker, and why?
It increases the amount of internal energy because it does not allow the heat to boil the water.
Which of the following would best describe the conductive properties of wood?
It is a good insulator.
Which generally expands more for an equal increase in temperature: solids or liquids?
Liquids generally expand more than solids.
If you touch the metal sides in an oven with your bare hand, you're in trouble. But hold your hand briefly in the oven air and you're okay. What does this tell you about the relative conductivity of metal and air?
Metal is a good conductor of heat, whereas air is a terrible conductor of heat.
Water will boil spontaneously in a vacuum - on the surface of the Moon, for example. Could you cook an egg in this boiling water? Explain.
No. Food is cooked by high water temp, not the boiling process. In vacuum water can boil at normal room temperature. So, on the surface of the Moon boiling food is not an effective way of cooking.
Since all objects emit energy to their surroundings, why don't the temperatures of all objects continuously decrease?
Objects what are good emitters are equally good absorbers, so they absorb radiation as was as emit it.
Calculate the quantity of heat absorbed by 30 g of water that warms from 30 ∘C to 90 ∘C.
Q = mcΔT m = 30 g C = 1 cal/g*C ΔT = 90 - 30 = 60 ∘C Q = (30 g) x (1 cal/g*C) x (60 ∘C) Q = 1800 cal (final answer)
The quantity of heat Q that changes the temperature ΔT of a mass mm of a substance is given by Q=cmΔT, where cc is the specific heat capacity of the substance. For example, for H2O, c=1cal/g∘C. And for a change of phase, the quantity of heat Q that changes the phase of a mass mm is Q=mL, where L is the heat of fusion or heat of vaporization of the substance. For example, for H2O, the heat of fusion is 80 cal/g (or 80 kcal/kg) and the heat of vaporization is 540 cal/g (or 540 kcal/kg). Use these relationships to determine the number of calories to change 1.4 kg of 100∘C boiling water to 1.4 kg of 100∘C steam.
Q =mL=1.4*540= 760 kcal.
You wish to warm 45 kg of water by 20∘C for your bath. Select the correct equations that show that the amount of heat needed is 900 kcal ( 900 Cal).
Q=cmΔT=(1kcal/(kg⋅∘C))(45kg)(20∘C)=900kcal (heat energy = specific heat capacity x mass x temp. change)
The specific heat capacity of steel is 450 J/kg⋅∘C. Select the correct equations that show that the amount of heat needed to raise the temperature of a 14-kg piece of steel from 0 ∘C to 100 ∘C is 630,000 J.
Q=cmΔT=(450J/kg⋅∘C)(14kg)(100∘C−0∘C)=630,000J
The quantity of heat Q that changes the temperature ΔT of a mass mm of a substance is given by Q=cmΔT, where cc is the specific heat capacity of the substance. For example, for H2O, c=1cal/g∘C. And for a change of phase, the quantity of heat Q that changes the phase of a mass mm is Q=mL, where L is the heat of fusion or heat of vaporization of the substance. For example, for H2O, the heat of fusion is 80 cal/g (or 80 kcal/kg) and the heat of vaporization is 540 cal/g (or 540 kcal/kg). Use these relationships to determine the number of calories to change 1.4 kg of 0∘C ice to 0∘C ice water
Q=mL=1.4*80= 110 kcal.
The quantity of heat Q that changes the temperature ΔT of a mass mm of a substance is given by Q=cmΔT, where cc is the specific heat capacity of the substance. For example, for H2O, c=1cal/g∘C. And for a change of phase, the quantity of heat Q that changes the phase of a mass mm is Q=mL, where L is the heat of fusion or heat of vaporization of the substance. For example, for H2O, the heat of fusion is 80 cal/g (or 80 kcal/kg) and the heat of vaporization is 540 cal/g (or 540 kcal/kg). Use these relationships to determine the number of calories to change 1.4 kg of 0∘C ice to 1.4 kg of 100∘C steam.
Q=mLice+mc(T2-T1)+mLsteam= 110+140+760= 1000 kcal
The quantity of heat Q that changes the temperature ΔT of a mass mm of a substance is given by Q=cmΔT, where cc is the specific heat capacity of the substance. For example, for H2O, c=1cal/g∘C. And for a change of phase, the quantity of heat Q that changes the phase of a mass mm is Q=mL, where L is the heat of fusion or heat of vaporization of the substance. For example, for H2O, the heat of fusion is 80 cal/g (or 80 kcal/kg) and the heat of vaporization is 540 cal/g (or 540 kcal/kg). Use these relationships to determine the number of calories to change 1.4 kg of 0∘C ice water to 1.4 kg of 100∘C boiling water.
Q=mc(T2-T1)= +(1.4*1*100)=140 kcal.
A great amount of water vapor changes phase to become water in the clouds that form a thunderstorm. Does this release thermal energy or absorb it?
Release thermal energy. One gram of boiling water requires 540 calories of heat to vaporize. This is called the latent heat of vaporization. The same quantity of heat is released when one gram of water vapor changes phase to the liquid state. So, condensation in the clouds releases large amounts of thermal energy.
Why does warm, moist air form clouds when it rises?
Rising air expands and cools. Water drops condense when moist air cools.
Desert sand is very hot in the day and very cool at night. What does this indicate about its specific heat capacity?
Sand has a low specific heat, as evidenced by its relatively large temperature changes for small changes in internal energy.
What is sublimation? Is it a heating or cooling process?
Sublimation is when the fastest molecules at the surface of a solid have escape velocity and leave to become a gas. It leaves behind the slower, cooler molecules.
How would decreasing the percentage of greenhouse gases affect the amount of infrared radiation reflected by the atmosphere back toward Earth?
The amount of infrared radiation would decrease.
How would increasing the density of air in the atmosphere affect the amount of infrared radiation returned by the atmosphere back toward Earth?
The amount of infrared radiation would increase.
What would the consequences of completely eliminating the greenhouse effect?
The average temperature of the surface of Earth would drop to -18°C.
Why is one able to walk on red-hot coals without getting one's feet burned?
The coals are not good conductors of heat.
What happens to the hexagonal open structure of ice when sufficient pressure is applied to it?
The crystals are crushed to form the liquid phase.
Why is it important to protect water pipes in the winter so that they don't freeze?
The expansion of the water as it freezes can potentially rupture the pipes.
How is the energy value of foods determined?
The food is burned and the energy released is measured.
Northeastern Canada and much of Europe receive about the same amount of sunlight per unit area. Why, then, is Europe generally warmer in the winter?
The gulf stream carries warm, high heat capacity water past the west coast of Europe.
What cooks food faster in a pressure cooker?
The higher temperature of boiling water under pressure cooks the food faster.
Looking at the expansion joint in the photo of the following figure, would you say it was taken on a warm day or a cold day? Why?
The photo was probably taken on a warm day. This bridge has an expansion joint to account for the expansion of the bridge due to heat. You can see how it is mildly stretched in the picture.
How does the pressure exerted by bubbles in the water compare with the atmospheric pressure when the temperature of water in an open pressure cooker is below 100∘ C and when it equals 100∘ C?
The pressure exerted by the bubbles is less than the atmospheric pressure below 100∘ C and equals the atmospheric pressure at 100∘ C
Discuss why water can issue from deep underwater vents at temperatures of some 300∘C without boiling.
The pressure of surrounding water acts like a pressure cooker and prevents boiling.
Why does the direction of coastal winds change from day to night?
The specific heat of water is greater than the specific heat of land. Water cools more slowly at night. The temperature difference drives convection and offshore winds.
What happens when you heat water that is at 0∘C?
The temperature increases until it reaches 100∘C
What happens when you heat ice that is at -40∘C?
The temperature increases until the ice reaches its melting point.
What happens when you heat ice that is at 0∘C?
The temperature stays constant until all the ice is melted.
What happens when you heat water that is at 100∘C?
The temperature stays constant until all the water is boiled.
Why are mittens warmer than gloves on a cold day?
There is more air space in mittens than gloves, which makes for warmer hands. Also, the fingers in mittens are next to one another, making the hand warmer
In an insulated container, liquid water is mixed with ice. What can you conclude about the phases present in the container when equilibrium is established?
There is no way of knowing the phase composition without more information.
Is there a distinction between thermal energy and internal energy? Which term do physicists prefer?
Thermal energy emphasizes heat flow, whereas internal energy is the grand total of all energies inside a substance. Physicists prefer internal energy.
How does this compare with the heat needed to raise the temperature of the same mass of water through the same temperature difference?
This value is less than the heat needed to raise the temperature of the same mass of water through the same temperature difference.
If you were to wish to save fuel and you're going to leave your cool house for a half hour or so on a very hot day, should you turn your air-conditioning thermostat up a bit, turn it off altogether, or let it remain at the room temperature you desire?
Turn the air conditioner off altogether to keep T small. Heat leaks at a faster rate into a cold house than into a not-so-cold house. The greater the rate at which heat leaks into the house, the greater the amount of fuel consumed by the air conditioner.
Which of the following changes would make the water balloon more likely to pop? (Ignore effects of convection within the fluid.)
Use a liquid that has a lower heat capacity than water. Use a thicker balloon.
How would you walk on red-hot coals without getting your feet burned?
Walk fast
Why does a piece of watermelon stay cool for a longer time than sandwiches do when both are removed from a picnic cooler on a hot day?
Water in the melon has more "thermal inertia" which means it has a higher specific heat than the sandwich ingredients. There is more water in the watermelon, which takes longer to change temperatures.
Why is evaporation a cooling process?
When the fastest molecules leave during evaporation, the slower, cooler ones remain.
Is it possible for heat to flow between two objects with the same internal energy? Can heat flow from an object with less internal energy to one with more internal energy? Defend your answers.
Yes, both cases, as long as one higher temperature than the other. Differences in temperature, not internal energy, dictates heat flow.
What kind of strip is Dr. Hewitt holding in his hand?
a strip consisting of brass on one side and steel on the other, welded together
If you were able to grab a hot pan and pull it out by the handle without burning yourself, what kind of handle must the pan have, and why?
a wooden handle, because it is the better insulator.
The final temperature of the water is __________.
between T1 and T2
Which will normally warm faster: a black pot of cold water or a silvered pot of cold water? Which will cool faster?
black, black
You are mixing water with ice in an insulated container. The temperature of the ice is initially below its freezing point. The following are given: - the amount of heat absorbed by the ice if heated to its melting point: 400 J, - the amount of heat absorbed by the ice if it all melts (which includes the heat needed to bring the ice to its melting point): 2100 J, - the amount of heat given off by the water if cooled to its freezing point: 1800 J, and - the amount of heat given off by the water if it all freezes (which includes the heat needed to bring the water to its freezing point): 5200 J. Based on this information, at equilibrium, which phases are present?
both ice and water
A thermos bottle controls heat transfer by _____________.
conduction, convection, and radiation
Newton's law of cooling applies to objects that undergo _____________.
cooling or warming
When air rapidly expands, its temperature normally ___________.
decreases
What type of gas absorbs and re-emits infrared radiation?
greenhouse gas
Find the height from which a block of ice should ideally be dropped to completely melt it that falls without air drag. [Hint: Equate the joules of gravitational potential energy to the product of the mass of ice and its heat of fusion (in SI units, 335,000 J/kgJ/kg). Do you see why the answer doesn't depend on mass?] Does the answer depend on mass?
h = 34 km No
In lab you submerge 100 g of 42 ∘C iron nails in 100 gg of 18 ∘C water (the specific heat of iron is 0.12 cal/g∘C.) Equate the heat gained by the water to the heat lost by the nails and find the final temperature of the water. Your lab partner is surprised by the result and says that since the masses of iron and water are equal, the final water temperature should lie closer to 30 ∘C∘C, half-way between. What is your explanation?
heat lost: 42 ∘C --> x ∘C (0.12 cal/g*C) x (100 g) x (42 - x ∘C) = 504 - 12x heat gained: 18 ∘C --> x ∘C (1.0 cal/g*C) x (100 g) x (x - 18 ∘C) = 100x - 1800 T: (504 - 12x) = (100x - 1800) 112x = 2304 T (x) = 21 ∘C (final answer) The masses are equal, but the specific heat capacities are not.
You are mixing water with ice in an insulated container. The temperature of the ice is initially below its freezing point. The following are given: - the amount of heat absorbed by the ice if heated to its melting point: 6400 J, - the amount of heat absorbed by the ice if it all melts (which includes the heat needed to bring the ice to its melting point): 14,100 J, - the amount of heat given off by the water if cooled to its freezing point: 1800 J, and - the amount of heat given off by the water if it all freezes (which includes the heat needed to bring the water to its freezing point): 5200 J . Based on this information, at equilibrium, which phases are present?
ice only
When an air molecule is hit by an approaching, faster moving molecule, does the approaching molecule's rebound speed increase or decrease? How about when it hits a receding molecule?
increase, decrease
What happens when Dr. Hewitt heats up the strip?
it bends
Water with a mass of 0.500 kg at 15.0∘C is mixed with 0.800 kg of water at 35.0∘C. What is the final temperature Tf of the mixture?
m1 = 0.8 kg T1 = 35 C m2 = 0.5 kg T2 = 15 C T = (cw m1T1 + cw m2T2) / (cw m2 + cwm1) final temperature:T = 27.3 C
Suppose that we replace the aluminum with a mystery metal and repeat the experiment in the video. As in the video, the mass of the metal is the same as that of the water. Room temperature is about 20∘C before the start of the experiment. The water heats up to 40∘C, and the mystery metal heats up to 80∘C. Compared to that of water, the heat capacity of our mystery metal is
one-third as great.
Radioactive decay of granite and other rocks in Earth's interior provides sufficient energy to keep the interior molten, to heat lava, and to provide warmth to natural hot springs. This is due to the average release of about 0.03 JJ per kilogram each year. Find an increase in temperature for a thermally insulated chunk of granite that takes about 13.0 million years to change temperature. (Assume that the specific heat capacity cc of granite is 800 J/kg⋅C∘. Use the equation Q=cmΔT.)
q1=0.03 J/kg.yr T = 13.0 x 10^6 yrs C = 800 J/kg*K m = 1.0 kg Q= q1 × T Q = 0.03 x (13.0 x 10^6) Q = 3.9 x 10^5 J Q=mcΔT ΔT = Q/mc ΔT = (3.9 x 10^5)/800 ΔT = 488 ∘C (final answer)
Relatively speaking, do high-frequency waves have long wavelengths or short wavelengths? Name an electromagnetic wave the higher frequency than blue light.
short, ultraviolet
What are the four common phases of matter?
solid, liquid, gas, plasma
What do you use a pressure cooker for?
to prevent boiling and cooling
Changes of phase most always require _________.
transfer of energy
You are mixing water with ice in an insulated container. The temperature of the ice is initially below its freezing point. The following are given: - the amount of heat absorbed by the ice if heated to its melting point: 400 J, - the amount of heat absorbed by the ice if it all melts (which includes the heat needed to bring the ice to its melting point): 2100 J, - the amount of heat given off by the water if cooled to its freezing point: 2400 J, and - the amount of heat given off by the water if it all freezes (which includes the heat needed to bring the water to its freezing point): 5200 J. Based on this information, at equilibrium, which phases are present?
water only
Which of the following most prevents the escape of terrestrial radiation?
water vapor
