Physics Concepts - Chapters 10, 11, 12
At what common temperature will a block of wood and a block of metal both feel neither hot nor cold to the touch? 1. At the freezing point 2. When the temperature of the blocks is the same as the temperature of your hand 3. When the temperature of the blocks is lower than the temperature of your hand 4. When the temperature of the blocks is higher than the temperature of your hand 5. At room temperature
2 It's the temperature difference that causes items to feel hot or cold to the touch.
A metal spoon is dropped into a shallow pot of boiling water and its temperature increases to 100◦ C. Assume the heat added to the spoon is exactly equal to the increase in the spoon's internal energy. How much work does the spoon do in the process? 1. Unable to determine 2. No work 3. > 0 4. < 0
2 Q = U, so U = Q - W W = 0
A glass of water sits on a table. The temperature of the water is the same as that of the glass. Which would move faster, the silicon dioxide (SiO2) molecules that make up the glass or the water (H2O) molecules? 1. Silicon dioxide molecules 2. Water molecules 3. They move at the same speed.
2 Since they are at the same temperature, they have the same average kinetic energy. The water molecules move faster because they have a lower molecular mass (10) than a silicon dioxide molecule (34).
Hot water/steam radiators are common fixtures that nicely warm the interiors of buildings. These radiators warm a room primarily 1. via radiation. 2. via convection. 3. via conduction. 4. about equally.
2 The exposed pipework of the radiator is brought to a high temperature by steam or hot water. Air near the radiator is warmed by conduction. The placement of the radiator in a room allows the newly heated air to rise away from the radiator, drawing cooler air toward it. The radiator warms the cool air and the process continues. This is convection! Radiators are often painted with highly reflective silverish paint to reduce radiation and allow the radiator pipes to become and remain hotter than they otherwise would, increasing their ability to drive convection.
After they are heated for a long time, which object has the highest temperature? 1. The cotton piece 2. They all have the same temperature. 3. The metal piece 4. The wood piece
2. they all have the same temp as the oven
A large parking lot contains 50 identical cars. Which is a higher entropy situation? 1. Either 2. Unable to determine 3. When the cars are allowed to park anywhere 4. When the cars are forced to park between the lines in designated spaces
3 There are many more arrangements of cars when they can park anywhere than when they are forced to park in designated spots
(Part 2) Did the temperature increase? 1. Unable to determine 2. Yes; the internal energy increased 3. No; not all of the ice melted 4. No; the internal energy didn't change
3 Because the heat added only melted some of the ice, the temperature is still 0 C.
The greenhouse effect occurs when 1. ultraviolet light is absorbed by the atmosphere. 2. cooling towers malfunction. 3. steam heating systems are used. 4. radiated heat from the Earth is absorbed by the atmosphere.
4
Which object has the lowest temperature? 1. The wood piece 2. The metal piece 3. The cotton piece 4. They all have the same temperature.
4 They have the same temperature as the air.
Monatomic Gas
can store energy as motion in three different directions
Substance A has twice the specific heat of substance B. Equal masses of the two substances, at different temperatures, are placed in thermal contact and allowed to come to equilibrium. (a) What is the ratio Qb/Qa of the energy transferred to (or from) the samples. (b) What is the ratio Tb/Ta of their temperature changes
(a) -1 (b) -2 (since substance A has twice the specific heat, the temperature change for substance B is going to be twice as big compared to that of the temperature change of substance A) the temperature change is smaller for the one that has the larger specific heat. Energy is conserved. Because energy is conserved, the Q will be equal to one another. We don't know which one is positive and which is negative. They are going to be equal and opposite.
Cups of water for coffee or tea can be warmed with a coil that is immersed in the water and raised to a high temperature by means of electricity. (a) Why do the instructions warn users not to operate the coils in the absence of water? (b) Can the immersion coil be used to warm up a cup of stew?
(a) The operation of an immersion coil depends on the convection of water to maintain a safe temperature. As the water near a coil warms up, the warmed water floats to the top due to Archimedes' principle. The temperature of the coil cannot go higher than the boiling temperature of water, 100 C. If the coil is operated in air, convection is reduced, and the upper limit of 100 C is removed. As a result, the coil can become hot enough to be damaged. (b) NO. If the coil is used in an attempt to warm a thick liquid like stew, convection cannot occur fast enough to carry energy away fro the coil, so that it again may become hot enough to be damaged.
11.1 Suppose you have 1 kg each of iron, glass, and water, and all three samples are at 10 C. (a) Rank the samples from lowest to highest temperature after 100 J of energy is added to each by heat. (b) Rank them from least to greatest amount of energy transferred by heat if enough energy is transferred so that each increases in temperature by 20 C.
(a) Water, glass, iron - base this off of their specific heats. water has the highest specific heat. Because of this, its change in temperature will be the least. Likewise, iron has the lowest specific heat, thus its temperature change will be the greatest after 100 J (q) is added. (b) Iron, glass, water - this is because you multiply 20 degrees by its C. so water will be the greatest since it has the greatest c.
Figure shows Maxwell speed distributions for three different samples of oxygen gas. (a) is the temperature of sample B greater than, less than, or equal to the temperature of sample A? (b) Is the temperature of sample C greater than, less than, or equal to the temperature of sample A?
(a) equal to if related to the velocity, A and B are the same. So the temp is the same. (b) greater than The velocity in C is greater than A. Therefore, its temperature is going to be greater than that of A.
The measurement of the average kinetic energy of the molecules in a substance is called 1. temperature. 2. conduction. 3. internal energy. 4. convection.
1
Suppose a new liquid were discovered that is identical to water in every way except that it has a lower latent heat of fusion. Would it take a longer or shorter time to make ice out of this liquid in your freezer? 1. Shorter 2. It depends on other factors, also. 3. Longer
1 It would take less time to freeze; however, it would also take less time to melt, so the new liquid might be less useful. This is because Q = mL
Which of the following has the greatest amount of internal energy? 1. A laptop 2. An iceberg 3. A cup of hot coffee 4. A pencil 5. A cup of cold water
2 A cup of hot coffee has a highest temperature, but not a greatest internal energy. Although the iceberg has less internal energy per mass, its enormous mass gives it a great amount of total energy.
What do you say about the temperature of water at the bottom of Niagara Falls? 1. a little lower than the temperature at the top 2. a little higher than the temperature at the top 3. much higher than the temperature at the top 4. it's impossible to predict without a measurement 5. much lower than the temperature at the top 6. the same as the temperature at the top
2 Ignoring other effects, the temperature should be slightly higher because the potential energy of the water above has been trans- formed to kinetic energy below, which in turn is transformed to internal energy when the falling water is stopped.
Tom says that it is impossible to maintain constant temperature while the container is being compressed. Is this true? 1. Yes; the temperature will always decrease. 2. Yes; the average kinetic energy of the molecules increases because the the external force does positive work. 3. No; the average kinetic energy of the molecules could remain the same if some heat were removed from the gas.
3 Normally compressing a gas rapidly will increase its temperature. If the temperature of the gas is to remain constant as the gas is being compressed, heat must be removed from the gas.
You use energy to heat your home. What ultimately happens to the energy that you pay for in your heating bill? 1. the energy heats your home 2. the energy changes to mass 3. the energy escapes your home and heats the outside 4. The energy disappears as it never exists.
3 At first, the energy heats your home. However, that heat eventually escapes your home and heats the outside. Eventually it is distributed over a larger portion of the Earth and the universe.
A closed, rigid container contains an ice-water mixture at 0 ◦C. Heat is added slowly and some, but not all, of the ice melts. Did the internal energy increase or decrease? 1. It remained the same. 2. It decreased. 3. It increased. 4. Unable to determine
3 By the first law of thermodynamics, the internal energy increased
One hundred grams of liquid A is at a temperature of 100◦C. One hundred grams of liquid B is at a temperature of 0◦C. When the two liquids are mixed, the final temperature is 50◦C. What can you say about the specific heats of the two liquids? 1. The specific heat of B is greater than that of A. 2. The specific heat of A is greater than that of B. 3. The specific heats of A and B are equal.
3 Heat is mc∆T. The heat that escaped from A is equal to the heat gained by B. The masses and temperature changes are the same, so the specific heats must also be the same.
Which of the following statements is/are correct? A) There is no limit to how low a temperature can fall. B) There is no limit to how high a temperature can rise. C) The more thermal insulation that is put in an unheated house, the slower it will cool when the outside temperature falls. D) The more thermal insulation that is put in an non-cooled house, the slower it will heat when the outside temperature rises. E) Heat can be transferred into a liquid by having microwave radiation immerse the liquid, or by having a jet of gas stopped by the liquid. 1. C and D only. 2. A and E only. 3. All but A. 4. All but A and B. 5. B and E only.
3 the absolute lower limit to temperature is 0 K, absolute zero.
Consider two equal-sized rooms connected by an open door. One room is maintained at a higher temperature than the other. Which room contains more air molecules? 1. Both rooms contain the same number of air molecules. 2. It's impossible to determine. 3. The hotter room 4. The cooler room
4 A greater number of slower-moving molecules in the cooler room would produces an air pressure at the door equal to a fewer number of faster-moving molecules in the warmer room.
Three objects are kept outside for a long time on a cold day: a piece of cotton, a piece of wood, and a piece of metal. Which object feels the coldest when you touch it? 1. The cotton piece 2. The wood piece 3. They all feel the same. 4. The metal piece
4 Metal has the smallest thermal conductivity, so heat exchange between the finger and the metal is faster; it feels colder when you touch it.
You have three pots of boiling water on the stove. Which one has the lowest temperature? 1. The one that is boiling water vigorously 2. The one that has been boiling the longest time 3. The one which is just barely boiling 4. They all have the same temperature
4 water boils at 100 C
If the pressure on a gas in a flexible closed container is increased and the temperature remains constant, what happens to the volume of gas? 1. Decreases at first, then increases 2. Increases 3. Remains the same 4. Increases at first, then decreases 5. Decreases
5 For constant temp, the volume decreases if the pressure increases.
A balloon, originally of volume Vi, inflates at constant pressure, P , to twice its original radius. The amount of work done by the balloon is: 1. 2 P Vi 2. 3 P Vi 3. P Vi 4. 5 P Vi 5. 7 P Vi
5 The amount of work done in an isobaric process is W = P(Vf-Vi) the initial volume is r^3 the final volume is (2r)^3 = 8r^3 So Vf = 8 Vi and W = P(8Vi - Vi) = 7 PVi
Under constant pressure and with a constant amount of gas present, what happens to the volume of the gas if the temperature increases? 1. Decreases 2. Remains the same 3. Decreases at first, then increases 4. Increases at first, then decreases 5. Increases
5 Under constant pressure, the volume must increase if the temperature increases. according to the ideal gas law PV/T = constant
Identical amounts of thermal energy are added to each of three isolated, equal mass samples A, B and C of unknown substances. If their temperature changes are ordered as Tb>Tc>Ta, which sample has the largest specific heat.
A specific heat and temperature change are inversely proportionate. Therefore, since A has the smallest temperature change, that means its specific heat is largest.
12.2 Identify the paths A, B, C, and D in Figure as isobaric, isothermal, isovolumetric, or adiabatic. For path B, Q = 0
A is isovolumetric, B is adiabatic, C is isothermal, D is isobaric isobaric the pressure stays the same so no change in pressure so it is a horizontal line isovolumetric the volume stays the same so no change in volume so a vertical line.
A tile floor may feel uncomfortably cold to your bare feet, but a carpeted floor in an adjoining room at the same temperature feels warm. Why?
A tile floor may feel uncomfortably cold to your bare feet, because the loss of temperature when the heat flows from your body to the tile floor and the tile floor behaves like a good conductor of heat. But a carpeted floor in the next room at the same temperature can make you feel warm because no temperature difference takes place due to the carpeted floor is not a heat conductor. Tile is a better conductor of energy than carpet so the tile conducts energy away from your feet more rapidly than does the carpeted floor.
Why do vapor bubbles in a pot of boiling water get larger as they approach the surface?
Additional water vaporizes into the bubbles, so that the number of moles n increases. Because they are restrained by less liquid pressure from the surrounding water at the top compared to the bottom. Hence, the vapor gas is free to expand to a greater volume. Remember, pressure in fluids, in situations of fluid statics is due to each layer of fluid supporting all the layers of fluid above it.
When a sealed Thermos bottle full of hot coffee is shaken, what changes, if any, take place in (a) the temperature of the coffee and (b) its internal energy?
Although no energy is transferred into or out of the system by heat, work is done on the system as the result of the agitation. Consequently, both the temperature and the internal energy of the coffee increase.
Markings to indicate length are placed on a steel tape in a room that is at a temperature of 22 C. Measurements are then made with the same tape on a day when the temperature is 27 C. Are the measurements too long, too short, or accurate?
As temperature increases steel expands. (if you want to be precise the coefficient of length expansion for steel is 1.2*10-5 K-1). Therefore, the measurement taken when the temperature was 22oC will not be the same compared to the measurements taken when the temp was 27oC. When the temp is 27oC the lengh of the measuring tape will be longer thus the measurements taken will be too short. Too short. Heat causes material to expand. Since the original markings were placed at 22 degrees and the it is now at 27 degrees, the metal expanded. That means the marks will be farther apart. You'll get fewer of them for a given length. So all of the measurements will be short.
Figure shows a metal washer being heated by a Bunsen burner. The red arrows in options a, b, and c indicate the possible directions of expansion caused by the heating. Which option correctly illustrates the washer's expansion?
As the washer is heated, all dimensions increase, including the radius of the hole. Option A correctly illustrates the washer's expansion.
An automobile radiator is filled to the brim with water when the engine is cool. What happens to the water when the engine is running and the water has been raised to a high temperature?
As the water rises in temperature, it expands or rises in pressure or both. The excess volume would spill out of the cooling system, or else the pressure would rise very high indeed. The expansion of the radiator itself provides only a little relief, because in general solids expand far less than liquid for a given positive change in temperature The water expands and spills out, because the water expands in volume more than the steel radiator. Change in volume = Initial volume x coefficient of expansion x change in temperature Since coefficient of expansion of water is greater than that of steel, the expansion in water will be greater than expansion of steel radiator for same change in temperature. Thus water expands and spills out, because the water expands in volume more than the steel radiator.
The US penny is now made of a copper coated zinc. Can a calorimetric experiment be devised to test for the metal content in a collection of pennies? If so, describe the procedure.
For pennies minted in 1982, when both copper and zinc cents were made. The safest and best way to tell their composition is to weigh them. Copper pennies weigh is 3.11 grams (+/- 0.13 g), whereas the zinc pennies weigh only 2.5 grams (+/- 0.1 g). No, a calorimeter experiment can be devised to test for the metal content in a collection of pennies. Given that, the specific heat differential between zinc and copper is only 1%, it is my opinion that a calorimetric experiment would lack proper precision to yield a usable result. No, you can't really tell because the specific heat is so close. but the masses are different so it would be better to test based off of weighing it.
Using the first law of thermodynamics, explain why the total energy of an isolated system is always constant.
If the system is isolated, no energy enters or leaves the system by heat, work, or other transfer processes. Within the system, energy can change from one form to another, but since energy is conserved, these transformations cannot affect the totally amount of energy. The total energy is constant.
For an ideal gas in an isothermal process, there is no change in internal energy. Suppose the gas does work W during such a process. How much energy is transferred by heat?
If there is no change in internal energy, then, according to the first law of thermodynamics, the heat is equal to the negative of the work done on the gas (and thus equal to the work done by the gas). Thus, Q = -W = W *by gas* the amount of work you do is equal to the amount of heat since delta U is zero bc it is an isothermal process.
Suppose the volume of an ideal gas is doubled while the pressure is reduced by half. Does the internal energy of the gas increase, decrease, or remain the same? Explain.
Initially the pressure is P, volume V, their product is PV Later pressure becomes p/2, volume 2V, their product is P/2*2V =PV the state equation PV = m/M*RT shows, PV constant means T isunchanged. The internal energy of ideal gas only depends on T, *therefore the internal energy remains the same* The internal energy of the gas remains constant when thevolume of an ideal gas is doubled while the pressure is reduced byhalf. Ideal gas PV = nRT P V = constant P1 V1 = P2V2 dQ = dU + dW dU = dQ - dW It depends whether the expansion is adiabatic or isothermal. An adiabatic change happens rapidly and does not allow heat energy to leave or enter the system. So in this case the internal energy would fall as the gas does work on expanding. If it is an isothermal change, which is done slowly at constant temperature, heat energy enters the system and the internal energy remains constant.
Suppose you compress a gas, doing 100 Joules of work on the gas. If 100 Joules of heat are allowed to escape during the compression, what is the change in internal energy? 1. ∆E = 0 2. ∆E > 0 3. Unable to determine 4. ∆E < 0
Let: W = 100 J and Q = 100 J U = Q-W or 100J-100J = 0J
Some thermometers are made of a mercury column in a glass tube. Based on the operation of these common thermometers, which has the larger coefficient of linear expansion, glass or mercury?
Mercury must have the larger coefficient of expansion. As the temperature of a thermometer rises, both the mercury and the glass expand. If they both had the same coefficient of linear expansion, the mercury and the cavity in the glass would expand by the same amount, and there would be no apparent movement of the end of the mercury column relative to the calibration scale on the glass. if the glass expanded more than the mercury, the reading would go down as the temperature went up! Now that we have argued this conceptually, we can look in a table and find that the coefficient for mercury is about 20 times larger as that for glass, so that the expansion of the glass can sometimes be ignored. mercury has the largest coefficient of linear expansion than glass because when temperature is measured then mercury expands more than the glass containing it
The objects are all placed in an oven heated to 90◦C and left for a long time. Which object will feel the warmest? 1. They all feel the same. 2. The cotton piece 3. The metal piece 4. The wood piece
Metal has the smallest thermal conductivity, so heat exchange between the finger and the metal is faster; it feels warmer when you touch it.
A rubber ballon is blown up and the end tied. Is the pressure inside the balloon greater than, less than, or equal to the ambient atmospheric pressure? Explain.
Once inflated with regular, atmospheric air, the air inside the balloon will have a greater air pressure than the original atmospheric air pressure. Air pressure, technically, is a measurement of the amount of collisions against a surface at any time. In the case of balloon, it's supposed to measure how many particles at any in any given time space collide with the wall of the balloon and bounce off. However, since this is near impossible to measure, air pressure seems to be easier described as density. The similarity comes from the idea that when there are more molecules in the same space, more of them will be heading towards a collision course with the wall. if the pressure on the outside was greater, then the balloon would pop!
Objects A and B have the same size and shape with emissivities eA and eB and temperatures Ta and Tb, respectively. (a) If eA=eB and Tb=4Ta, what is the ratio Pb/Pa of their radiated powers? (b) If, instead, they radiate the same power and eA=4eB, what is the ratio Tb/Ta of their Kelvin temperatures?
P = (sigma)(A)(e)(Ta^4 - Tb^4) a) since Pressure and Temperature are directly proportional you can just set the ratio with the temp. being Tb^4/Ta^4. so that give you 1:64 b) eATa = eBTb so (Tb/Ta)^4 = eB/eA 4^4/1 = 64:1
A container filled with an ideal gas is connected to a reservoir of the same gas so that the number of moles in the container can change. If the pressure and volume of the container are each doubled while the temperature is held constant, what is the ratio of the final to the initial number of moles in the container?
PV = nRT P1V2 = P2V2 If you increase P and V by two then you get: 4 P2 and V2 decrease by 4 so n2 is increased by a factor of four. The ratio of the final to initial number of moles is 4:1
Is it possible to construct a heat engine that creates no thermal pollution?
Practically speaking, it isn't possible to create a heat engine that creates no thermal pollution, because there must be both a hot heat source (energy reservoir) and a cold heat sink (low-temperature energy reservoir). The heat engine will warm the cold heat sink and will cool down the heat source. If either of those two events is undesirable, then there will be thermal pollution. Under some circumstances, the thermal pollution would be negligible. For example, suppose a satellite in space were to run a heat pump between its sunny side and its dark side. The satellite would intercept some of the energy that gathered on one side and would dump it to the dark side. Since neither of those effects would be particularly undesirable, it could be said that such a heat pump produced no thermal pollution. It is possible to wholly convert a given amount of mechanical energy into thermal energy. For example, when a car comes to a stop on a level road, friction and air resistance change all of its kinetic energy into thermal energy. According to the second law of thermodynamics it is not possible to wholly convert a given amount of thermal energy into mechanical energy. For example, only about 5% of the thermal energy that enters an automobile engine is converted to kinetic energy of the car. 2nd law says that you will always give in more than what you take out. there is always inefficiency with a transfer of energy. friction based, something will make you lose energy (W/Q must equal zero to be perfectly efficient. and it can only be that way if there is an infinite amount of temp or absolute zero)
Clearly distinguish among temperature, heat, and internal energy.
Temperature is a measure of molecular motion. Heat is energy in the process of being transferred between objects by random molecular collisions. Internal energy is an object's energy of random molecular motion and molecular interaction.
Metal lids on glass jars can often be loosened by running hot water over them. Why does that work?
The coefficient of expansion for metal is generally greater than that of glass; hence, the metal lid loosens because it expands more than the glass. heat expands things with greater coefficients of expansion.
Consider the human body performing a strenuous exercise, such as lifting weights or riding a bicycle. Work is being done by the body, and energy is leaving by conduction from the skin into the surrounding air. According to the first law of thermodynamics, the temperature of the body should be steadily decreasing during the exercise. That isn't what happens, however. Is the first law invalid for this situation? Explain.
The energy that is leaving the body by work and heat is replaced by means of biological processes that transform chemical energy in the food that the individual ate into internal energy. Thus, the temperature of the body can be maintained. Delta U=Q-W The change in the internal energy of a system is equal to net energy added as heat to the system minus the net work done by the system. Now although body does work while doing exercise(W), but glucose is broken to produce energy(Q) in the body. So Delta U>0 generally and there is increase in temperature under these processes only a small amount turns into mechanical energy so you heat up
The first law of thermodynamics says we can't get more out of a process than we put in, but the second law says that we can't break even. Explain this statement.
The first law is a statement of conservation of energy that says that we cannot devise a cyclic process that produces more energy than we put into it. If the cyclic process takes in energy by heat and puts out work, we call the device a heat engine. In addition to the first law's limitation, the second law says that, during the operation of a heat engine, some energy must be ejected to the environment by heat. As a result, it is theoretically impossible to construct a heat engine that will work with 100% efficiency.
12.5 Suppose you are throwing two dice in a friendly game of craps. For any given throw, the two numbers that are face-up can have a sum of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, or 12. Which outcome is most probably? Which is least probably?
The number 7 is the most probable outcome. The numbers 2 and 12 are the least probably outcomes
What is wrong with the following statement: "Given any two bodies, the one with the higher temperature contains more heat."
The object with the higher temperature contains more energy, but heat is the transfer of energy between two objects at different temperatures. Heat is the flow of energy, not a measure of the average kinetic energy of the molecules (which is temperature). temp and heat are NOT equivalent since temperature is the average heat of the molecules in a substance.
10.5 Why doesn't the melting of ocean-based ice raise as much concern as the melting of land-based ice.
Unlike land-based ice, ocean-based ice already displaces water, so when it melts, ocean levels won't change much
On a clear, cold night, why does frost tend to form on the tops, rather than the sides, of mailboxes and cars?
Water molecules in the air are constantly bouncing off of surrounding surfaces. If a surface is cold enough, the molecules will stick to the surface rather than bouncing off. Once a layer of frozen molecules form, new molecules will tend to align themselves with those already there, forming regular crystals. The temperature of the surface is determined by the net heat balance on it, which is a function of air temperature, air movement, radiation, and solid conduction. Usually the ground is warmer than the air, and the air tends to be the strongest effect, but a surface isolated from the ground on a clear, still night will be dominated by radiation to the sky, so it can get colder than the air. That's why you see frost on top of the mailbox or on the tips of the grass when there is none on the ground.
Objects deep beneath the surface of the ocean are subjected to extremely high pressures, as we saw in Topic 9. Some bacteria in these environments have adapted to pressures as much as a thousand times atmospheric pressure. How might such bacteria be affected if they were rapidly moved to the surface of the ocean?
We can think of each bacterium as being a small bag of liquid containing bubbles of gas at a very high pressure. The ideal gas law indicates that if the bacterium is raised rapidly to the surface, then its volume must increase dramatically. In fact, the increase in volume is sufficient to rupture the bacterium. the pressures on the inside and the outside have to cancel out or be equal and opposite.
On a very hot day, it's possible to cook an egg on the hood of a car. Would you select a black car o a white car on which to cook your egg? Why?
We must select the hood of the black car to cook the egg. The surface or bodies with black color absorbs more radiation and reflects very less from the sun or any other source. On the other hand a white surface will reflect most of the radiation. Hence we can easily gather enough energy to cook our egg in a less amount of time if we use the hood of the black car compared to that of white. a black body does not reflect radiation at any wavelength, any light coming from it is due to atomic and molecular vibrations alone black absorbs heat and emits it to cook the egg. whereas the white will reflect it off.
Rub the palm of your hand on a metal surface for 30 to 45 seconds. Place the palm of your other hand on an unrubbed portion of the surface and then on the rubbed portion. The rubbed portion with feel warmer. Now repeat this process on a wooden surface. Why does the temperature difference between the rubbed and unrubbed portions of the wood surface seem larger than for the metal surface?
When you rub the surface, you increase the temperature of the rubbed region. With the metal surface, some of this energy is transferred away from the rubbed site by conduction. Consequently, the temperature in the rubbed area is not as high for the metal as it is for the wood, and it feels relatively cooler than the wood. the metal diffuses the heat throughout the whole thing (conduction) whereas the wood will not spread out the heat. Thats why the temp difference between the rubbed and unrubbed portions of the wood surface seems larger
A window air conditioner is placed on a table inside a well insulated apartment, plugged in and turned on. What happens to the average temperature of the apartment? a) It increases b) It decreases c) It remains constant d) It increases until the unit warms up and then decreases e) The answer depends on the initial temperature of the apartment
a you always have more heat coming out while it is trying to cool the apartment down but since the apartment is closed it will heat up the apartment and not decrease it.
(a) Why does an ordinary glass dish usually break when placed on a hot stove? (b) Dishes made of Pyrex glass don't break as easily. What characteristic of Pyrex prevents breakage?
a material expands and contracts due to its temperature. when normal glass is heated or cooled unevenly, the different regions experience stress due to the uneven expansion/contraction. Pyrex glass has a smaller coefficient of expansion. it doesn't change its size as much due to temperature thus it does not experience as much stress A) an ordinary glass dish will usually break because of the stressed that build up as the glass expands when heated. Heat makes things expand. B) the expansion coefficient for Pyrex glass is much lower than that of ordinary glass. Thus, the Pyrex dish will expand much less than the dish of ordinary glass and does not normally develop sufficient stress to cause breakage.
Two identical containers each hold 1 mole of an ideal gas at 1 atm. Container A holds a monatomic gas and container B holds a diatomic gas. The gas in each container is compressed at constant pressure to half its original volume. (a) What is the ratio Wa/Wb of the work done on gas A to the work done on gas B? (b) What is the ratio Ua/Ub of the change in internal energy for gases A and B? (c) What is the ratio Qa/Qb of the energy transferred to gases A and B?
a) 1 this is because W = PV. As you decrease the volume by 2 you also increase the pressure by 2 so the work stays the same. b) 3/5 monatomic has 3 degrees of freedom and diatomic has 5. c) 5/7
11.5 Stars A and B have the same temperature, but star A has twice the radius of star B. (a) What is the ratio of star A's power output to star B's output due to electromagnetic radiation? The emissivity of both stars can be assumed to be 1. (b) Repeat the question if the stars have the same radius, but star A has twice the absolute temperature of star B. (c) What's the ratio if star A has both twice the radius and twice the absolute temperature of star B?
a) 4 b) 16 c) 64
The first law of thermodynamics is U = Q + W. For each of the following cases, state whether the internal energy of an ideal gas increases, decreases, or remains constant: (a) No energy is transferred to the gas as it expands to twice its original volume. (b) The gas volume is held constant while energy Q is removed. (c) The gas volume is held constant and no energy is transferred to or from the gas. (d) The gas temperature increases.
a) Decrease internal energy? You are increasing the volume, thus decreasing the pressure which decreases the temperature. Therefore, you decrease the heat Q which decreases the internal energy U. No energy is being transferred to the system so Q is zero. The thing is expanding, the gas is doing work. Therefore the work done ON the gas is negative. Since Q is equal to 0, the internal energy is = to the work done on the gas. So the internal energy decreases. b) If you decrease the Q then you are taking out the heat change so it would probably decrease the internal energy. c) I think that the internal energy would stay constant if the volume does not change and no energy is transferred. d) If the temperature increases then the Q would increase, thus increasing the internal energy. Temp is directly related to the internal energy heat and temp is NOT the same thing.
A sealed container contains a fixed volume of monatomic ideal gas. If the gas temperature is increased by a factor of two, what is the ratio of the final to the initial (a) pressure (b) average molecular kinetic energy (c) root-mean-square speed, and (d) internal energy
a) PV=nRT Because of this the pressure should also increase by a factor of two. 2:1 b) Temperature of a gas is a direct measure of the average molecular kinetic energy of the gas. Because of this, the average molecular kinetic energy will increase by a factor of two. 2:1 c) Root mean square speed = Square root of (3RT/M) Because of this equation, an increase in temperature will also increase the root-mean-square speed. Probably by the square root of 2. d) Internal Energy U for a monatomic gas: U = (3/2)nRT So if you increase the Temperature by a factor of two, you increase by a factor of 2. 2:1
The air we breathe is largely composed of Nitrogen and Oxygen molecules. The mass of an N2 molecule is less than the mass of an O2 molecule. (a) For air at 300 K, is the average kinetic energy of an N2 molecule greater than, less than, or equal to the average kinetic energy of an O2 molecule? (b) Is the rms speed in air of an N2 molecule greater than, less than, or equal to the rms speed in air of an O2 molecule.
a) Since the molecular mass of N2 is less than that of O2, the average kinetic energy will be less for that of an N2 molecule than that of an O2 molecule. This is because temperature is directly proportional to average kinetic energy. If the temperature for both is the same, they will depend on the molecule mass. b) Square root of (3RT/M) . If you decrease the denominator like with N2, you will keep the overall number greater under the square root, thus making the rms speed in air of an N2 molecule greater than that of an O2 molecule.
The first law of thermodynamics
an energy conservation law that relates to changes in internal energy any Q exchanged between the system and the environment and any work done through the expansion or compression of the system results in a change in the internal energy energy, U, of the system. If a system undergoes a change from an initial state to a final state, then the change in the internal energy U is given by U = Q + W where Q is the energy exchanged between the system and the environment, and W is the work done on the system.
A heat engine does work Weng while absorbing energy Qh from the hot reservoir and expelling energy Qc to the cold reservoir. Which one of the following is impossible? a) Qh>Qc>Weng b) Qh> W eng>Qc c) W eng = Qc d) Weng > Qh e) Weng > Qc
an engine is taking heat energy and putting it into the cold reservoir. B is what the thing is actually doing. D is probably not possible. Because you cannot do more work than the original energy you are given!
Diatomic Gas
aside from moving in three directions, it can also tumble, rotating it in two different directions. these are called degrees of freedom
An ideal gas is compressed to half its initial volume by means of several possible processes. Which of the following processes results in the most work done by the gas? a) isothermal b) adiabatic c) isobaric d) the work done is independent of the process
b In adiabatic process, there is no heat exchange with the surrounding which means that the temperature and hence internal energy increases. This means that the work is done not only to compress the gas but also to increase the internal energy. Thus, work done is maximum for adiabatic process than for isothermal process and the least in isobaric process.
Equal masses of substance A at 10 C and substance B are 90 C are placed in a well-insulated container of negligible mass and allowed to come to equilibrium. If the equilibrium temperature is 75 C, which substance has the larger specific heat? a) substance A b) substance B c) the specific heats are identical d) the answer depends on the exact initial temperatures c) more info needed
b Since they are both exchanging the same amount of energy we need to look at the equation and how it relates to temperature.. c = Q/mT Q is constant for both. (energy) For substance A the Q is divided by a greater temperature so the specific heat is going to be smaller. For substance B the Q is divided by a smaller temperature, thus the specific heat is going to be larger. smaller change in temperature has a larger specific heat.
10.6 One container is filled with argon gas and another with helium gas. Both containers are at the same temperature. Which atoms have the higher rms speed? a) argon b) helium c) they have the same speed d) not enough information to say?
b helium has a smaller molecular mass than argon thus, it will have a higher root mean square speed.
12.4 Which of the following is true for the entropy change of a system that undergoes a reversible, adiabatic process? a) S < 0 b) S = 0 c) S > 0
b in adiabatic processes, there is no change in Q aka it is zero, thus S is equal to zero.
12.1 By visual inspection, order the PV diagrams shown in figure from the most negative work done on the system to the most positive work done on the system. a. a, b, c, d b. a, c, b, d c. d, b, c, a d. d, a, c, b
b notice that the graphs all have the same endpoints, but the areas beneath the curves are different, the work done on a system depends on the path taken in the PV diagram When the volume expands, work is negative. (a and c) When the volume compresses, work is positive ( b and d)
11.2 Calculate the slopes for the A, C, and E portions of Figure. Rank the slopes from least to greatest and explain what your ranking means a) A, C, E b) C, A, E c) E, A, C d) E, C, A
b the slopes are proportional to the reciprocal of the specific heat, so a larger specific heat results in a smaller slope, meaning more energy is required to achieve a given temperature change. - the specific heat of steam (E) is the smallest which means that it has the greatest change in temperature. they are able to conduct temperature and energy changes very easily. Water doesn't conduct energy and temp as much. It retains the energy the sun brings. it is a good insulator. This is because its specific heat is so high that it doesnt change temp easily.
10.2 If you quickly plunge a room-temperature mercury thermometer into very hot water, the mercury level will a) go up briefly before reaching a final reading b) go down briefly before reaching a final reading, or c) not change
b ??
11.4 Two rods of the same length and diameter are made from different materials. The rods are to connect two regions of different temperature so that energy will transfer through the rods by heat. They can be connected in series, or in parallel. In which case is the rate of energy transfer by heat larger? a) When the rods are in series b) When the rods are in parallel c) The rate is the same in both cases
b - one is able to conduct heat more easily. the parallel configuration allows the better conductor of heat to skip the other one and transfer heat energy from one end to another more quickly.
10.1 Two objects with different sizes, masses, and temperatures are placed in thermal contact. Choose the best answer: Energy travels a) from the larger object to the smaller object b) from the object with more mass to the one with less mass c) from the object at higher temperature to the object at lower temperature.
c
11.3 Will an ice cube wrapped in a wool blanket remain frozen for (a) less time, (b) same length of time, or (c) a longer time than an identical ice cube exposed to air at room temperature
c
12.3 Three engines operate between reservoirs separated in temperature by 300 K. The reservoir temperatures are as follows: Engine A: Th = 1000 K, Tc = 700 K Engine B: Th = 800 K, Tc = 500 K Engine C: Th = 600 K, Tc = 300 K Rank the engines in order of their theoretically possible efficiency, from highest to lowest. a. A, B, C b. B, C, A c. C, B, A d. C, A, B
c A: .3 B: .375 C: .5
10.3 If you are asked to make a very sensitive glass thermometer, which of the following working fluids would you choose? a) mercury b) alcohol c) gasoline d) glycerin
c in a gas thermometer, the temperature readings are nearly independent of the substance used in the thermometer.
10.4 Two spheres are made of the same metal and have the same radius, but one is hollow and the other is solid. The spheres are taken through the same temperature increase. Which sphere expands more? a) solid sphere b) hollow sphere c) they expand by the same amount d) not enough information to say
c same material and same radius. Delta L = aL DELTA T
An ideal gas undergoes an adiabatic process, there is no change in internal energy. Suppose the gas does work W during such a process. How much energy is transferred by heat? a) Because no energy is added by heat, the temperature cannot change. b) The temperature increases if the gas volume increases c) The temperature increases if the gas pressure increases d) The temperature decreases if the gas pressure increases e) The temperature decreases if the gas volume decreases.
c temp has to go up when pressure goes up. So A is wrong. since PV= nRT Pressure is directly related to temperature.
Different amounts of thermal energy are added to each of three isolated samples A, B, and C of lead. If the energy transfers are ordered as Qb> Qc > Qa and each sample undergoes the same temperature change, which sample has the largest mass?
c = Q/mT (QA) If all are lead they have the same specific heat. If they all have the same change in temperature then we must focus on the change in energy. If Qb has the greatest change in energy, then I would conclude that it has the smallest mass, therefore Qc is the middle amount of mass, and Sample A of lead, having the smallest energy transfer would have the largest mass.
A person shakes a sealed, insulated bottle containing coffee for a few minutes. What is the change in the temperature of the coffee? a) a large decrease b) a slight decrease c) no change d) a slight increase d) a large increase
d (d) A slight increase in temperature because kinetic energy of molecules increase due to shaking. as kinetic energy is directly proportional to temperature
Which of the following statements is true? (a) The path on a PV diagram always goes from the smaller volume to the larger volume. (b) The path on a PV diagram always goes from the smaller pressure to the larger pressure. (c) The area under the path on a PV diagram is always equal to the work done on a gas. (d) The area under the path on a PV diagram is always equal in magnitude to the work done on a gas.
d Area = P (Vf-Vi) = PV The area under the graph in a PV diagram is equal in magnitude to the work done on the gas.
A poker is a stiff, nonflammable rod used to push burning logs around in a fireplace. Suppose it is to be made of a single material. For best functionality and safety, should he poker be made from a material with (a) high specific heat and high thermal conductivity, (b) low specific heat and low thermal conductivity, (c) low specific heat and high thermal conductivity, (d) high specific heat and low thermal conductivity, or (e) low specific heat and low density?
d you want something with a low conductivity because it needs to be a good insulator so it doesn't burn you for specific heat, you want something with a low change of temp because you want the rod to stay cold. and if the temp is low then the C(specific heat) is going to be high. c = Q/T they are indirectly proportionate.
Star A has twice the radius and twice the absolute temperature of star B. What is the ratio of the power output of star A to that of star B? The emissivity of both stars can be assumed to be 1. a) 4 b) 8 c) 16 d) 32 e) 64
e 1. Total power output or luminosity of a star is directly proportional to its surface area and to the fourth power of its absolute temperature. 2. Surface area of a sphere is proportional to the radius squared. Therefore, the ratio of the power output of Star a to Star b PA/PB = (R²a) (T^4a) / (R²b) (T^4b) PA/PB = (2Rb²) (2Tb) ^4 / (R²b) (T^4b) = 64 Correct answer = E.64 A = pi R^2 that gives you 2^2 or 4 Temperature is raised 2^4 and that is 16 16 x 4 = 64
In a calorimetry experiment, three samples A, B and C with Ta>Tb>Tc are placed in thermal contact. When the samples have reached thermal equilibrium at a common temperature T, which of the following must be true? a) Qa>Qb>Qc b) Qa<0, Qb<0 and Qc>0 c) T> Tb d) T<Tb e) Ta>T>Tc
e - this is because Ta is greater than T and Tc is less than T. Ta wont go any higher than the final temp to equilibriate. Tc has to go higher to equilibriate. c, d, and e are wrong because they do not take into account phase change?? since Tc is the smallest it has to go up since T is greater than C. We aren't s
Objects A and B with Ta>Tb are placed in thermal contact and come to equilibrium. (a) For which object does the entropy increase? (b) For which object does the entropy decrease? (c) Which object has the greater magnitude of entropy change?
entropy is S = Q/T a) if the temperature is greater for object A, that means that the entropy will be smaller for A. Therefore, the entropy would increase for object B. b) entropy would decrease for object A c) if you already increase the entropy in B you will make it bigger.
Entropy
is related to the second law of thermodynamics the entropy of the Universe increases in all natural processes. a disorderly arrangement is much more probable than an orderly one if the laws of nature are allowed to act without interference. isolated systems tend toward greater disorder and entropy is a measure of that disorder. in all real processes, the energy available for doing work decreases.
Figure shows a composite bar made of three different materials that connects a hot reservoir at 100 C to a cold reservoir at 0 C. If the sections A, B, and C all have the same dimensions and the temperatures shown in the figure are constant, rank the thermal conductivities from largest to smallest.
kB>kA>kC why? Substances that are good conductors have large thermal conductivities, whereas good insulators have low thermal conductivities. So because B has the smallest change in temperature(it is able to transfer energy the most efficiently), it is the largest thermal conductor. The heat very easily traveled through B where it did not travel easily through A. A has the second largest change in temp therefore it is the second largest thermal conductors. C doesn't allow for the temperature to change easily. Therefore C is a really good insulator. if it is a good insulator then it will have the lowest thermal conductivity.
A thermodynamic process occurs in which the entropy of a system changes by -6 J/K. According to the second law of thermodynamics, what can you conclude about the entropy change of the environment? a) it must be +6 J/K or less b) It must be equal to +6 J/K. c) It must be between +6 J/K and 0 d) It must be 0 e) It must be +6 J/K or more
the entropy of any isolated system always increases. since we decrease it on one side it will increase on the other side. so e. at least +6 or more. energy you cannot break even with but entropy will always be more disordered.
Metabolic Rate
the metabolic rate U/t is the rate at which chemical potential energy in food and oxygen are transformed into internal energy to just balance the body losses of internal energy by work and heat. it is directly proportional to the rate of oxygen consumption by volume
The second law of thermodynamics
we can't break even No heat engine operating in a cycle can absorb energy from a reservoir and use it entirely for the performance of an equal amount of work. efficiency = W/Qh must always be less than one. It is theoretically impossible to construct a heat engine with an efficiency of 100%
Q is positive
when energy is transferred into the system
Q is negative
when the energy is removed from the system