Question 1

"Two objects in thermal equilibrium with a third object are in thermal equilibrium with each other." Which Law of Thermodynamics is this?
A) Zeroth
B) First
C) Second
D Third

Accepted Answer

This statement is a description of the Zeroth Law of Thermodynamics, which establishes the concept of temperature and thermal equilibrium.

Question 2

"The entropy of an isolated system never decreases." Which Law of Thermodynamics is this?
A) Zeroth
B) First
C) Second
D Third

Accepted Answer

This statement is a formulation of the Second Law of Thermodynamics, which states that the total entropy of an isolated system can never decrease over time, and is constant if and only if all processes are reversible.

Question 3

Which Law of Thermodynamics relates change in internal energy to heat added to a system and work done by it?
A) Zeroth
B) First
C) Second
D Third

Accepted Answer

The First Law of Thermodynamics relates the change in internal energy of a system to the heat added to the system and the work done by it, essentially stating that energy cannot be created or destroyed, only transformed.

Question 4

What does a heat pump not do?
A) Increase entropy
B) Move heat from a low temperature region to a high temperature region
C) Perform work on its surroundings
D) Conserve energy

Accepted Answer

Heat pumps are designed to move heat from a cooler area to a warmer area using work, typically electrical energy, but they do not perform work on their surroundings in the sense of mechanical work output; instead, they consume work to transfer heat.

Question 5

You open the refrigerator in your room and put in a case of room-temperature root beer. After an hour, the root beer is ice cold. If your room air did not exchange any heat with the outdoor air during that time, the room air will be
A) colder because the refrigerator reverses natural heating, so that things get colder rather than hotter.
B) colder because as the refrigerator struggles to cool the root beer, some of the cold it produces inevitably leaks out into the room as the result of imperfect insulation.
C) warmer because the refrigerator will have pumped heat out of the root beer and into the room air.
D) warmer because some of the heat from the root beer inevitably leaks out into the room as the result of imperfect insulation.

Accepted Answer

The refrigerator works by removing heat from its interior (where the root beer is) and expelling it into the surrounding environment (the room air). This process results in the room air becoming warmer.

Question 6

Which of the following quantities is not conserved?
A) Energy
B) Angular momentum
C) Entropy
D) Momentum

Accepted Answer

Entropy is not conserved; it generally increases in isolated systems according to the second law of thermodynamics.

Question 7

You fill two identical mugs with coffee, but the coffee in one mug is at a higher temperature than that in the other mug. You place the two mugs simultaneously in a microwave oven and turn it on briefly. As a result, you add 1 joule of thermal energy to each mug. Which mug experiences the larger increase in entropy (if any)?
A) The two mugs experience equal increases in entropy.
B) The mug containing the colder coffee experiences the larger increase in entropy.
C) Neither mug experiences any increase in entropy.
D) The mug containing the hotter coffee experiences the larger increase in entropy.

Accepted Answer

The increase in entropy for a given amount of energy is larger at lower temperatures, so the mug with the colder coffee experiences a larger increase in entropy.

Question 8

The air in this room consists of countless tiny, independent molecules. You can be sure that all the oxygen molecules will not all shift spontaneously to the other side of the room (leaving you without oxygen) because that would
A) violate Newton's laws of motion.
B) be extremely unlikely and therefore violate the 2nd law of thermodynamics.
C) violate Bernoulli's equation.
D) not conserve energy and therefore violate the 1st law of thermodynamics.

Accepted Answer

The second law of thermodynamics states that the total entropy of an isolated system can never decrease over time, and is constant if and only if all processes are reversible. The spontaneous movement of all oxygen molecules to one side of the room would represent a significant decrease in entropy (a more ordered state), making it extremely unlikely to occur, thus violating the second law of thermodynamics.

Question 9

Suppose that you place a timer and a tiny pile of gunpowder in an absolutely rigid box. You then seal the box completely and insulate it perfectly so that no heat can flow in or out of the box. Soon the timer ignites the gunpowder and it burns to form smoke. Since the box is sealed, the smoke remains inside it. If you look into the box a few minutes later, you will find that the smoke has not converted back into the gunpowder because
A) there is not enough energy in the box to reform the gunpowder.
B) there are not enough atoms in the box to reform the gunpowder.
C) such an event, unburning the smoke to form gunpowder, is extraordinarily unlikely.
D) the basic laws of motion, otherwise known as Newton's three laws, forbid the unburning of smoke to form gunpowder.

Accepted Answer

The transformation of smoke back into gunpowder is an example of a process that is highly improbable due to the laws of thermodynamics, particularly the second law, which implies that in an isolated system, processes tend to move towards a state of maximum entropy or disorder. Reversing the burning process would decrease entropy, which is extremely unlikely to happen spontaneously.

Question 10

It is a hot summer day and your friend's apartment has no air conditioning. However, a brand new refrigerator lies unopened in the center of the living room. Being a creative person, your friend closes all the doors and windows of the apartment, unpacks the refrigerator, plugs it in, and turns it on. Your friend then opens the refrigerator door and uses a small fan to circulate the air past the refrigerator and throughout the room. After the refrigerator has operated for a few minutes, the average temperature in the room is
A) lower than it was before.
B) higher than it was before.
C) the same as it was before and the temperature is uniform throughout the room.
D) the same as it was before, but some regions are hotter and others are colder.

Accepted Answer

Refrigerators remove heat from their interior and release it into the surrounding environment. By opening the door and using a fan to circulate air, the heat expelled by the refrigerator's external coils increases the room's average temperature.

Question 11

A thermoelectric cooler is a type of heat pump that uses electric power to move heat against its natural direction of flow. In other words, it takes energy from a system and transfers it to another system which is at a higher temperature. In such a heat pump
A) the entropy of the system must be conserved.
B) Newton's laws of motion prevent heat from moving from a cool region to a warm region.
C) the cooler requires power input because the flow of heat from a cool region to a warm region alone would decrease the entropy (disorder) of the system.
D) the cooler requires power input the flow of heat from a cool region to a warm region alone would violate the conservation of energy.

Accepted Answer

The cooler requires power input because moving heat from a cooler to a warmer region naturally decreases the system's entropy, which is against the second law of thermodynamics. This law implies that entropy, or disorder, tends to increase in an isolated system. To decrease entropy by moving heat "uphill" from cold to hot, external energy (in this case, electrical power) must be supplied.

Question 12

It is a warm summer day and you are having lunch outdoors on a patio. A window air conditioning unit hums quietly nearby as it cools an office inside the building. Your friend notices that the unit's outdoor part is emitting a considerable amount of heat and comments on how strange that is. You explain correctly that the air conditioner's outside part is emitting the heat
A) it produces from the electricity it consumes.
B) that is left over when it converts thermal energy from the inside air into electricity.
C) it removes from the inside air and the heat it produces from the electricity it consumes.
D) it produces during its defrost cycle; when it warms up its evaporator to remove ice that forms because of the humidity.

Accepted Answer

Air conditioners work by removing heat from the inside air and expelling it outside. Additionally, the process of running the air conditioner itself generates heat due to the electricity it consumes. This is why the outside part of an air conditioner emits heat.

Question 13

In a car engine, the compression stroke involves the piston compressing the air/gas mixture so rapidly that virtually no heat loss can occur. In the compression stroke, the air/gas mixture
A) heats because of friction between the gas and the cylinder.
B) cools because the gas is radiating its energy away.
C) heats because work is being done on the air/gas mixture.
D) cools because the air/gas mixture is doing work on the piston.

Accepted Answer

During the compression stroke in a car engine, the piston compresses the air/gas mixture, and as work is done on the mixture, its temperature increases. This is an application of the first law of thermodynamics, where work done on the system (in this case, the air/gas mixture) increases its internal energy, leading to a rise in temperature.

Question 14

Suppose you have an ideal gas which gives up heat energy as it does work on its surroundings. Must the temperature increase, decrease or can you not determine how the temperature will behave? Please explain.

Accepted Answer

The answer of Suppose you have an ideal gas which...

Question 15

Under what conditions can heat be removed from an ideal gas and have the temperature go up?

Accepted Answer

The answer of Under what conditions can heat be removed...

Question 16

Is it possible for an isothermal process to ever change the internal energy of an ideal gas? Please explain.

Accepted Answer

The answer of Is it possible for an isothermal process...

Question 17

Please make up four events that, were they to occur, would violate each of the four laws of thermodynamics.

Accepted Answer

The answer of Please make up four events that, were...

Question 18

Consider water that freezes into ice when put in your freezer, so the water goes from being disordered to being relatively ordered. Please explain if the freezing of the ice violated the second law of thermodynamics.

Accepted Answer

The answer of Consider water that freezes into ice when...

Question 19

An ideally efficient freezer cools food to 210K. If room temperature is 300K, and the machine consumes 75 J of work, how much heat was removed from the food?
A) 210 J
B) 75 J
C) 175 J
D) 300 J

Accepted Answer

The efficiency of an ideal refrigerator or freezer is given by the coefficient of performance (COP), which for a refrigerator is defined as $COP = \frac{Q_C}{W}$, where $Q_C$ is the heat removed from the cold reservoir (in this case, the food), and $W$ is the work input. The COP for an ideal refrigerator can also be expressed in terms of temperatures as $COP = \frac{T_C}{T_H - T_C}$, where $T_C$ is the temperature of the cold reservoir (210K in this case) and $T_H$ is the temperature of the hot reservoir (300K in this case). Rearranging the formula to solve for $Q_C$, we get $Q_C = COP \times W$. Substituting the values for $T_C$ and $T_H$ into the COP formula gives us $COP = \frac{210}{300 - 210} = \frac{210}{90}$. Therefore, $Q_C = \frac{210}{90} \times 75 = 2.333 \times 75 = 175 J$.

Question 20

An ideally efficient heater adds 1100 J of heat to a warm room. How much work does it perform if it removes 1400 J of energy from the outdoors?
A) 2800 J
B) 300 J
C) 400 J
D) 0 - this can't be done.

Accepted Answer

The work done by the heater is the difference between the energy removed from the outdoors and the heat added to the room: 1400 J - 1100 J = 300 J.

Quiz 8: Thermodynamics

"Two objects in thermal equilibrium with a third object are in thermal equilibrium with each other." Which Law of Thermodynamics is this?

"The entropy of an isolated system never decreases." Which Law of Thermodynamics is this?

Which Law of Thermodynamics relates change in internal energy to heat added to a system and work done by it?

What does a heat pump not do?

You open the refrigerator in your room and put in a case of room-temperature root beer. After an hour, the root beer is ice cold. If your room air did not exchange any heat with the outdoor air during that time, the room air will be

Which of the following quantities is not conserved?

The air in this room consists of countless tiny, independent molecules. You can be sure that all the oxygen molecules will not all shift spontaneously to the other side of the room (leaving you without oxygen) because that would

A thermoelectric cooler is a type of heat pump that uses electric power to move heat against its natural direction of flow. In other words, it takes energy from a system and transfers it to another system which is at a higher temperature. In such a heat pump

In a car engine, the compression stroke involves the piston compressing the air/gas mixture so rapidly that virtually no heat loss can occur. In the compression stroke, the air/gas mixture

Suppose you have an ideal gas which gives up heat energy as it does work on its surroundings. Must the temperature increase, decrease or can you not determine how the temperature will behave? Please explain.

Under what conditions can heat be removed from an ideal gas and have the temperature go up?

Is it possible for an isothermal process to ever change the internal energy of an ideal gas? Please explain.

Please make up four events that, were they to occur, would violate each of the four laws of thermodynamics.

Consider water that freezes into ice when put in your freezer, so the water goes from being disordered to being relatively ordered. Please explain if the freezing of the ice violated the second law of thermodynamics.

An ideally efficient freezer cools food to 210K. If room temperature is 300K, and the machine consumes 75 J of work, how much heat was removed from the food?

An ideally efficient heater adds 1100 J of heat to a warm room. How much work does it perform if it removes 1400 J of energy from the outdoors?