Misconceptual Questions Test 1

Which of the following happens when a material undergoes a phase change? (a) the temperature changes (b) the chemical composition changes. (c) heat flows into or out of the material (d) the molecules break apart into atoms

(c) Heat flows into or out of the material

A heat engine operates between a high temperature of about 600∘C and a low temperature of about 300∘C. What is the maximum theoretical efficiency for this engine? a) =100%. b) ≈66%. c) ≈50%. d) ≈34%. e) Cannot be determined from the given information.

(d)~34%

For objects at thermal equilibrium, which of the following is true? (a) Each is at the same temperature. (b) Each has the same internal energy (c) Each has the same heat (d) All of the above (e) None of the above

(a) Each is at the same temperature.

As heat is added to water, is it possible for the temperature measured by a thermometer in the water to remain constant? (a) Yes, the water could be changing phase. (b) No, adding heat will always change the temperature. (c) Maybe; it depends on the rate at which the hear is added. (d) Maybe; it depends on the initial water temperature.

(a) Yes, the water could be changing phase

Two equal-mass liquids, initially at the same temperature, are heated for the same time over the same stove. You measure the temperatures and find that one liquid has a higher temperature than the other. Which liquid has the higher specific heat? (a) the cooler one (b) the hotter one (c) both are the same

(a) the cooler one The two objects absorb the same amount of heat from the stove. From Eq. 14-2, given that the masses are the same, the object with the higher specific heat will experience the smaller temperature increase and will therefore be cooler.

One mole of an ideal gas in a sealed rigid container is initially at a temperature of 100°C. The temperature is then increased to 200°C. The pressure in the gas: (a) Remains constant (b) Increases by about 25% (c) doubles (d)triples

(b) increases by about 25% A common error is to treat the temperature as doubling. If the temperature doubled, the pressure would also double. However, the temperature is given in degrees Celsius, not kelvins. When the temperature is converted to kelvins, it is easy to see that the temperature only increases by about 25%, from 373 K to 437 K. The pressure then also increases by about 25%. (The actual amount is 26.8%.)

When an ideal gas is warmed from 20 degrees C to 40 degrees C, the gas's temperature T that appears in the ideal gas law increased by a factor: (a) of 2 (b) of 1.07 (c) that depends on the temperature scale you use

(b) of 1.07 The absolute (Kelvin) scale must be used in the ideal gas law. If the Celsius scale is used, it appears that the temperature has doubled. However, 0°C is an arbitrarily chosen point on the temperature scale and cannot be used to determine temperature ratios. When the temperatures are converted to kelvins (293 K and 313 K) it can be seen that their ratio is about 1.07.

When you put an ice cube in a glass of warm tea, which of the following happens? (a) cold flows from the ice cube into the tea (b) cold flows from the ice cube into the tea and hear flows from the tea into the ice cube (c) Heat flows from the tea into the ice cube. (d) Neither heat nor cold flows. Only temperature flows between the ice and the tea

(c) Heat flows from the tea into the ice cube.

Ten grams of water is added to ten grams of ice in an insulated container. Will all of the ice melt? (a) yes (b) no (c) more information is needed

(c) More information is needed The problem does not specify the initial temperatures of the ice and water. If the ice and water are both initially at 0°C, then none of the ice will melt, since heat will not transfer between them. Alternatively, if the ice is at 0°C and the water is at 100°C, then the water can provide Q = mc∆T = (0.010 kg)(4186 J/kg ⋅ C°)(100 C°) = 4186 J of heat as it cools to 0°C. The ice only needs Q = mL = (0.010 kg)(333 kJ/kg) = 3330 J to melt completely, so in this case all the ice would melt. Since the water could provide more heat than needed, you need to know the initial temperatures of the ice and water to determine just how much of the ice would melt.

A steel plate has a hole in it with a diameter of exactly 1.0-cm when the plate is at a temperature of 20 °C. A steel ring has an inner diameter of exactly 1.0-cm at 20°C. Both the plate and the ring are heated to 100°C. Which statement is true? (a)The hole in the plate gets smaller, and the opening in the ring gets larger (b) The opening in the ring gets larger, but we need the relative size of the plate and the hole to know what happens to the hole (c) The hole in the plate and the opening in the ring get larger (d) The hole in the plate and the opening in the ring gets smaller (e) The hole in the plate gets larger, and the opening in the ring gets smaller

(c) The hole in the plate and the opening in the ring get smaller -Both are the same material, starting at the same temperature and ending at the same temperature

An ideal gas is in a sealed rigid container. The average kinetic energy of the gas molecules depends most on: (a) the size of the container (b) the number of molecules in the container (c) the temperature of the gas (d) the mass of the molecules

(c) The temperature of the gas

Two beakers contain a mixture of ice and water at equilibrium. Beaker A has less ice than Beaker B. Which beaker is the coldest, or are they equal in temperature? (a) Beaker A (b) Beaker B (c) Equal

(c) equal temperatures

Heat is (a) a fluid called caloric (b) a measure of the average kinetic energy of atoms (c) the amount of energy transferred between objects as a result of a difference in temperature (d) an invisible, odorless, weightless substance (e) the total kinetic energy of an ideal gas

(c) the amount of energy transferred between objects as a result of a difference in temperature

Which of the following is not true about an ideal gas? (a) the average kinetic energy of the gas molecules increases as the temperature increases. (b) the volume of an ideal gas increases with temperature if the volume is held constant c) The pressure of an ideal gas increases with temperature if the volume is held constant (d) All gas molecules have the same speed at a particular temperature (e) The molecules are assumed to be far apart compared to their size

(d) All gas molecules have the same speed at a particular temperature

The Linear Expansion of a material depends on which of the following? (a) The length of the material (b) The change in temperature of the material (c) The type of material (d) All of the above (e) Both (b) and (c)

(d) All of the above. The equation is: ∆L=αL₀∆T

It has been a hot summer, so when you arrive at a lake, you decide to go for a swim even though it it nighttime. The water is cold. The next day, you go swimming again during the hottest part of the day, and even though the air is warmer the water is still almost as cold. Why? (a) Water is fairly dense compared with many other liquids. (b) Water remains in a liquid state for a wide range of temperatures. (c) Water has a high bulk modulus. (d) Water has a high specific heat.

(d) Water has a high specific heat

Radiation is emitted (a) only by glowing objects such as the Sun (b) only by objects whose temperature is greater than the temperature of the surroundings (c) only by objects with more caloric than their surroundings (d) by any object not at 0 K (e) only by objects that have a large specific heat

(d) by any object not at 0 K Radiation is emitted by all objects not at absolute zero. Very hot objects, such as the Sun, emit radiation in the visible spectrum, so they appear to be glowing. If the temperature of an object is less than that of its surroundings, it has a net gain in energy as it absorbs more radiation than it emits. However, it is still emitting radiation. The amount of radiation emitted is independent of the object's specific heat.

A typical thermos bottle as a thin vacuum space between the shiny inner flask (which holds a liquid) and the shine protective outer flask, often stainless steel. The vacuum space is excellent at preventing (a) conduction (b) convection (c) radiation (d) conduction and convection (e) conduction, convection, and radiation

(d) conduction and convection Heat is able to transfer through a vacuum by radiation, but heat requires a medium to transfer by conduction and by convection. Therefore, the vacuum in a thermos prevents heat loss by conduction and convection.

Two objects are made of the same material, but they have different massed and temperatures. If the objects are brought into thermal contact, which one will have the greater temperature change? (a) The one with the higher initial temperature (b) The one with the lower initial temperature (c) the one with the greater mass (d) the one with the lesser mass (e) the one with the higher specific heat (f) not enough information

(d) the one with the lesser mass As the two objects are in thermal contact, the heat given off by the hot object will equal the heat absorbed by the cold object. The objects have the same specific heat, so the heat transfer is proportional to the product of the mass of each object and its change in temperature. The object with the smaller mass will then have the larger temperature change

Two ideal gases, A and B, are at the same temperature. If the molecular mass of the molecules in gas A is twice that of the molecules in gas B, the molecules' root-mean-square speed is (a) the same in both gases (b) twice as great in A (c) 1.4 times greater in A (d) twice as great in B (e) 1.4 times greater in B

(e) 1.4 times greater in B Some students might erroneously relate the temperature of the gas to the velocity of the gas molecules and surmise that the rms speeds would be equal. However, when the two gases are at the same temperature, the molecules will have the same average kinetic energy. The kinetic energy is proportional to the mass of the molecule and the square of the rms speed. Since mass B is half the mass of A, the speed of molecules of mass B must be 2 ≈ 1.4 × greater than the speed of molecules of mass A.

The temperature of an ideal gas increases. Which of the following is true? (a) the pressure must decrease. (b) the pressure must increase. (c) The pressure must increase while the volume decreases. (d) the volume must increase while the pressure decreases (E) the pressure, the volume, or both may increase.

(e): The pressure, the volume, or both may increase A common misconception is that if the temperature increases, both the pressure and volume will increase. However, by the ideal gas law, when the temperature increases, the product of the pressure and volume must increase. .

An ideal gas undergoes an isothermal process. Which of the following statements are true? (i) No heat is added to or removed from the gas. (ii) The internal energy of the gas does not change. (iii) The average kinetic energy of the molecules does not change

(ii) and (iii)

When using the ideal gas law, which of the following rules must be obeyed? (a) Always use temperature in kelvins and absolute pressure. (b) Always use volume in m^3 and temperature in kelvins. (c) Always use gauge pressure and temperature in degrees Celsius. (d) Always use gauge pressure and temperature in kelvins. (e) Always use volume in m^3 and gauge pressure

Answer:(a) Always use temperature in kelvins and absolute pressure.

Two identical bottles at the same temperature contain the same gas. If bottle B has twice the volume and contains half the numbers of moles of gas as bottle A, how does the pressure in B compare with the pressure in A?

By the ideal gas law, when the temperature is held constant, the pressure is proportional to the number of moles and inversely proportional to the volume. If the second bottle has twice the volume with only half the number of moles, it would only experience one-fourth the pressure. Pb=¼Pa

Rod A has twice the diameter of rod B, but both are made of iron and have the same initial length. Both rods are now subjected to the same change in temperature (but remain solid). How would the change in the rods' lengths compare?

Rod A = Rod B

About what percentage of the heat produced by burning gasoline is turned into useful work by a typical automobile? a) 20% b) 50% c) 80% d) 90% e) Nearly 100%

a) 20% The text states that "real engines that are well designed reach 60 to 80% of the Carnot efficiency." The cooling system of the engine keeps the high temperature at about 120°C (400 K) and the exhaust is about room temperature (300 K). The maximum efficiency would then be around 25%. Eighty percent of this maximum would be closest to 20% efficient. Any of the other choices for this question are not reasonable.

Which of the following possibilities could increase the efficiency of a heat engine or an internal combustion engine? a) Increase the temperature of the hot part of the system and reduce the temperature of the exhaust. b) Increase the temperatures of both the hot part and the exhaust part of the system by the same amount. c) Decrease the temperatures of both the hot part and the exhaust part of the system by the same amount. d) Decrease the temperature of the hot part and increase the temperature of the exhaust part by the same amount. e) None of the above; only redesigning the engine or using better gas could improve the engines efficiency.

a) Increase the temperature of the hot part of the system and reduce the temperature of the exhaust and (c) Decrease the temperatures of both the hot part and the exhaust part of the system by the same amount. The maximum efficiency of an engine is given by equation eideal = 1−TLTH, which can be written in the form: e = (TH−TC)/TH.

An ideal gas undergoes an isothermal expansion from state A to state B. In this process a) Q>0,ΔU=0,W>0. b)Q>0,ΔU=0,W<0. c)Q=0,ΔU=0,W>0. d)Q=0,ΔU>0,W>0. e)Q=0,ΔU<0,W<0

a) Q>0,ΔU=0,W>0 In an isothermal process the internal energy remains constant (ΔU = 0). In an expansion the gas does work on the surroundings (W = 0). Since the internal energy is constant and the work is positive, the first law of thermodynamics requires the heat absorbed also be positive (Q = 0).

In a mixture of gases oxygen and helium, which statement is valid? (a) The helium atoms will be moving faster than the oxygen molecules, on average. (b) both will be moving at the same speed (c) the oxygen molecules will, on average be moving more rapidly than the helium atoms (d) the kinetic energy of helium atoms will exceed that of oxygen molecules (e) None of the above

answer: (a) The helium atoms will be moving faster than the oxygen molecules, on average. In the mixture, the oxygen molecules and helium atoms will be at the same temperature, which means that their average molecular kinetic energies will be the same. Since a helium atom has less mass than an oxygen molecule, the helium atoms will be moving faster than the oxygen molecules on average.

The rms speed of the molecules of an ideal gas: (a) is the same as the most probable speed of the molecules. (b) is always equal to the squared root of 2 times the maximum molecular speed. (c) will increase as the temperature of a gas increases. (d) All of the above

answer: (c) will increase as the temperature of a gas increases. The rms speed of a gas is an average molecular speed found by taking the square root of the average of the square of the molecule speeds. Consider a gas in which 2/3 of the molecules are at rest and 1/3 move at a constant speed. The most probable speed is 0, but the rms speed is greater than zero. Therefore, the most probable speed is not necessarily the rms speed, so (a) is false. The rms speed is an average speed; therefore, it will always be equal to or smaller than the maximum speed, so (b) is false. The temperature of a gas is determined by the average molecular kinetic energy. As the temperature increases, the molecular kinetic energy increases; therefore, the rms speed must also increase, so (c) is true.

Which statement is true regarding the entropy change of an ice cube that melts? a) Since melting occurs at the melting point temperature, there is no temperature change so there is no entropy change b) Entropy increases c) Entropy decreases

b) Entropy increase Heat must be added to the ice cube to melt it. The change in entropy is the ratio of the heat added to the temperature of the ice cube. Since heat is absorbed in the process, the entropy increases.

An ideal gas undergoes an adiabatic expansion, a process in which no heat flows into or out of the gas. As a result, a) the temperature of the gas remains constant and the pressure decreases b) both the temperature and pressure of the gas decrease c) the temperature of the gas decreases and the pressure increases d) both the temperature and plume of the gas increase (e) both the temperature and pressure of the gas increase

b) both the temperature and pressure of the gas decrease As the gas expands, its volume increases and it does work on the surroundings. Since no heat is absorbed while the gas does this work, the first law of thermodynamics says that the internal energy and temperature of the gas must decrease. For the volume to increase as the temperature decreases, the ideal gas law requires that the pressure also decrease.

Which is possible: converting (i) 100J of work entirely into 100J of near, (ii) 100 J of heat entirely into 100 J of work? a) only (i) is possible b) only (ii) is possible c) Both (i) and (ii) are possible d) neither are possible

c) both are possible According to the second law of thermodynamics, it is impossible for heat to be entirely converted into work in a cycle or a heat engine. However, the question does not specify that we must consider a complete cycle. In an isothermal process Q = W . In an isothermal compression work is entirely converted into heat, and in an isothermal expansion heat is entirely converted into work.

An ideal gas undergoes an isobaric compression and then an isovolumetric process that brings it back to its initial temperature. Had the gas undergone one isothermal process instead, a) the work done on the gas would be the same b) the work done on the gas would be less c) the work done on the gas would be greater d) Need to know the temperature of the isothermal process

c) the work done on the gas would be greater

On a very hot day, could you cool your kitchen by leaving the refrigerator door open? a) Yes, but it would be very expensive. b) Yes, but only if the humidity is below 50% . c) No, the refrigerator would exhaust the same amount of heat into the room as it takes out of the room. d) No, the heat exhausted by the refrigerator into the room is more than the heat the refrigerator takes out of the room.

d) No, the heat exhausted by the refrigerator into the room is more than the heat the refrigerator takes out of the room. A common misconception in this situation is not realizing that a heat cycle running in reverse, like a refrigerator, must have a high-temperature exhaust. Furthermore, that high-temp exhaust is the sum of the heat removed from the inside of the refrigerator, plus the work done by the refrigerator's compressor.

In an isobaric compression of an ideal gas, a)no heat flows into the gas b) the internal energy of the gas remains constant c) no work is done on the gas d) work is done on the gas e)work is done by the gas

d) work is done on the gas An isobaric process is one in which the pressure is kept constant. In a compression the volume of the gas decreases. By Eq. 15-3, the work done by the gas is negative, so an external force had to do work on the gas. In isobaric processes heat is allowed to flow into or out of the system and the internal energy changes.