PHY 1102 Test 2

Which represents the greater amount of energy, 1 J or 1 cal?
a. 1 J is equal to 1 cal
b. 1 cal
c. 1 J

c. 1 J
10-17

While a gas does 680 J of work on its surroundings, 850 J of heat is added to the gas. What is the change in the internal energy of the gas?

170 J
10-18

A block of wood and a block of metal have been sitting on a table for a long time. The block of metal feels colder to the touch than the block of wood. Does this mean that the metal is actually at a lower temperature than the wood? Explain.
a. Yes, the me

c. No, the metal is a better conductor of heat than the wood so it conducts heat away from the hand and feels cooler.
10-19

Heat is sometimes lost from a house through cracks around windows and doors. What mechanism of heat transfer (conduction, convection, or radiation) is involved?
a. conduction
b. convection

b. convection
10-20

What heat transfer mechanism (conduction, convection, or radiation) is involved when heat flows through a glass windowpane?
a. conduction
b. convection

10-21

Is it possible for heat to flow across a vacuum? (Select all that apply.)
a. Yes, heat transfer by conduction will occur through a vacuum.
b. Yes, heat transfer by radiation will occur through a vacuum.
c. Yes, heat transfer by convection will occur throu

b. Yes, heat transfer by radiation will occur through a vacuum.
c. Yes, heat transfer by convection will occur through a vacuum.
10-22

Which of these types of motors or engines are heat engines? (Select all that apply.)
a. an electric motor
b. an automobile engine
c. a steam turbine

b. an automobile engine
c. a steam turbine
11-1

Could a simple machine such as a lever, a pulley system, or a hydraulic jack be considered a heat engine? Explain.
a. Yes, they are heat engines because they convert mechanical energy into work.
b. No, although they convert mechanical energy into work the

b. No, although they convert mechanical energy into work they do not take in heat energy.
11-2

In one cycle, a heat engine takes in 900 J of heat from a high-temperature reservoir, releases 560 J of heat to a lower-temperature reservoir, and does 340 J of work. What is its efficiency?

38%
11-3

A heat engine with an efficiency of 38% does 420 J of work in each cycle. How much heat must be supplied from the high-temperature source in each cycle?

1105.26
11-4

In one cycle, a heat engine does 400 J of work and releases 520 J of heat to a lower-temperature reservoir.
(a) How much heat does it take in from the higher-temperature reservoir?
(b) What is the efficiency of the engine?

a. 920 J
b. 43.4%
11-5

Is it possible for the efficiency of a heat engine to equal 1? Explain.
a. Yes, according to the first law of thermodynamics a heat engine has an optimal efficiency of 1.
b. Yes, according to the second law of thermodynamics a heat engine has an optimal e

c. No, the heat engine would violate the second law of thermodynamics by allowing complete conversion of heat energy into work.
11-7

A Carnot engine takes in heat from a reservoir at 340�C and releases heat to a lower-temperature reservoir at 170�C. What is its efficiency?

28%
11-8

A Carnot engine operates between temperatures of 580 K and 400 K and does 100 J of work in each cycle.
(a) What is its efficiency?
(b) How much heat does it take in from the higher-temperature reservoir in each cycle?

a. 36%
b. ???????
11-9

Is it possible to cool a closed room by leaving the door of a refrigerator open in the room? Explain.
a. Yes, although inefficient for the size of the room, the refrigerator will remove heat from the warmer environment of the room and exchange it for cool

c. No, this will heat the room since the heat rejected by the refrigerator exceeds the heat removed from the inside of the refrigerator by the work done in operating it.
11-10

In each cycle of its operation, a refrigerator removes 11 J of heat from the inside of the refrigerator and releases 34 J of heat into the room. How much work per cycle is required to operate this refrigerator?

23 J
11-13

A typical electric refrigerator has a power rating of 460 W, which is the rate (in J/s) at which electrical energy is supplied to do the work needed to remove heat from the refrigerator. If the refrigerator releases heat to the room at a rate of 860 W, at

400W
11-14