Deck 8: Thermodynamics

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

Answer 1

Zeroth

Question 2

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

A) Zeroth
B) First
C) Second
D Third

Answer 2

Second
D Third

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

Answer 3

First

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

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.

Question 6

Which of the following quantities is not conserved?

A) Energy
B) Angular momentum
C) Entropy
D) Momentum

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.

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.

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.

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.

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.

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.

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.

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.

Question 15

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

Question 16

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

Question 17

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

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.

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

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.

Question 21

Suppose you claim to a friend that you have built a machine that follows the first law of thermodynamics - it converts heat energy directly into the same amount of work. Please comment as to whether you believe your friend or not.

Question 22

Suppose you stir 100 g of water and do 419 J of work on the system. Assuming no leakage of energy, what will the resulting change in water temperature be?

A) -1^o C
B) -1^o F
C) +1^o F
D) + 1^o C

Question 23

Suppose you try to cool your home in the summer by letting heat flow from your house to your neighbor's home. You will

A) Not get far, because of the zeroth law of thermodynamics
B) Not get far, because of the first law of thermodynamics
C) Have a cool house in a couple hours
D) Have a warmer house in a couple hours

Question 24

The first law of thermodynamics is a re - statement of the law of

A) conservation of momentum
B) thermal equilibrium
C) conservation of energy
D) averages

Question 25

Suppose 100 g of water does 419 J of work on a system. Assuming no leakage of energy, what will the resulting change in water temperature be?

A) -1^o C
B) -1^o F
C) +1^o F
D) + 1^o C

Question 26

The _______ two temperatures are the _______ it is to move heat from hot to cold.

A) higher; easier
B) higher; harder
C) closer; easier
D) closer; harder

Question 27

Please explain why, in the evaporator of an air conditioner the coils cool down

Question 28

Please explain why, in the condenser of an air conditioner the coils heat up

Question 29

How can you reduce knocking in you car's engine?

A) Get an oil change
B) Use higher-octane gasoline
C) Switch to diesel fuel
D) Tune the engine so that the gasoline pre-ignites

Question 30

To make it less likely that a car engine will "knock" (have its fuel/air mixture ignite too early), the engine is designed so that

A) the fuel/air mixture is not compressed too tightly.
B) the fuel/air mixture is compressed as tightly as possible.
C) the fuel/air mixture remains cold until the sparkplug fires.
D) the fuel/air mixture stays at atmospheric pressure until the sparkplug fires.

Question 31

Moments before it is ignited by the spark plug, the mixture of fuel and air inside an automobile cylinder is compressed to very high density. During the compression process, the mixture's

A) temperature stays the same but its pressure rises.
B) temperature rises dramatically and so does its pressure.
C) temperature drops dramatically but its pressure rises.
D) temperature rises dramatically but its pressure drops.

Question 32

Please explain why it may be a waste of money for someone to invest in a tank full of premium gasoline.

Question 33

Please explain why your car engine is generally more efficient when its ignition temperature is higher.

Question 34

Who invented the internal combustion engine?

A) Auto
B) Otto
C) Diesel
D) Kelvin

Question 35

The "strokes", or "cycles" in a four - stroke engine are

A) induction, compression, power, exhaust
B) ignition, compression, power, exhaust
C) ignition, induction, power, exhaust
D) vacuum, compression, ignition, exhaust

Question 36

Suppose your instructor comes to class having not had enough sleep the night before. He proceeds to tell you about a machine he has built which does work but releases no heat into the environment, and he even cites the first Law of thermodynamics for justification. Please use additional thermodynamics to make a scientific evaluation of his claim.

Question 37

What causes knocking in your car's engine?

A) The fuel ignites before it should.
B) The fuel ignites in the exhaust system.
C) A connecting rod bearing is loose.
D) The piston compresses the fuel / air mixture so that it is a liquid and the piston hits it.

Question 38

The _______ the temperature difference between hot and cold, the ________ the fraction of heat you can divert and transform into __________.

A) larger; temperature
B) larger; work
C) smaller; work
D) smaller; temperature

Question 39

A Diesel engine is more efficient that a gasoline engine because

A) It has a higher temperature and can therefore convert more heat into work.
B) It has a higher temperature and can therefore convert less heat into work.
C) It has a lower temperature and can therefore convert more heat into work.
D) It has a lower temperature and can therefore convert less heat into work.

Question 40

Please explain why your car engine is generally less efficient when its ignition temperature is lower.

Question 41

The burned gas does more work on the piston during the power stroke than the piston does on the air - fuel mixture during the compression stroke because

A) The pressure during the power stroke is much higher than that in the compression stroke.
B) The pressure during the power stroke is much lower than that in the compression stroke.
C) The piston's speed during the power stroke is much higher than that in the compression stroke.
D) The piston's distance traveled during the power stroke is much larger than that in the compression stroke.

Question 42

Having too high of a compression ratio in a car engine can cause

A) Knocking due to loose valves
B) Knocking due to postignition of the fuel.
C) Knocking due to preignition of the fuel.
D) Too low of a fuel combustion temperature.

Question 43

You wake up one morning simply tired that we are hooked on fossil fuels. You are talking with your best friend about alternative energy and he says that in some time, hydrogen will eliminate the need for other sources of energy. Please correctly comment.