Question 1

The thermal efficiency of a heat engine is given by

Accepted Answer

E

Question 2

A steam engine is operating at its theoretical maximum efficiency of 60%.If the waste heat has a temperature of 100 $\degree$F (38 $\degree$C),what is the temperature of the boiler?

Accepted Answer

The efficiency of a Carnot engine is given by 1 - (Tc/Th), where Tc is the cold reservoir temperature and Th is the hot reservoir temperature, both in Kelvin. Given the efficiency is 60% (0.6) and Tc is 38°C (311K), solve for Th: 0.6 = 1 - (311/Th), which gives Th = 778K, equivalent to 504°C.

Question 3

A lawn mower has a 6-horsepower engine (1 HP = 750 W).If the engine has an efficiency of 20%,and the throttle is such that the engine cycles 10 times a second,the heat that is expelled in one cycle is

Accepted Answer

A

Question 4

A refrigerator has a coefficient of performance of 4.If the refrigerator absorbs 30 cal of heat from the cold reservoir in each cycle,the heat expelled (in cal)into the heat reservoir is

Accepted Answer

The coefficient of performance (COP) is defined as:
COP = heat removed/ work done = Q2/W
where Q2 is the heat removed from the cold reservoir and W is the work done by the refrigerator. 
In this case, COP = 4, and Q2 = 30 cal. Solving for W, we get:
W = Q2/COP = 7.5 cal. 
The heat expelled into the heat reservoir is given by the first law of thermodynamics:
Q1 = Q2 + W = 30 + 7.5 = 37.5 cal.
Therefore, the answer is B.

Question 5

A Carnot cycle,operating as a heat engine,consists,in the order given,of

Accepted Answer

The answer of A Carnot cycle,operating as a heat engine,consists,in...

Question 6

An automobile engine operates with an overall efficiency of 12%.How much energy is delivered as waste heat (in gallons of gasoline)for each 10 gallons of fuel burned?

Accepted Answer

Out of 10 gallons of fuel burned, only 12% is converted into useful work, and the remaining 88% energy is lost as waste heat. Therefore, the amount of energy delivered as waste heat is 0.88 x 10 = 8.8 gallons of gasoline.

Question 7

A new electric power plant has an efficiency of 42%.For every 100 barrels of oil needed to run the turbine,how many are essentially lost as waste heat (in barrels of oil)to the environment?

Accepted Answer

Efficiency = (Useful energy output / Total energy input) x 100%
As the efficiency is 42%, the energy output = 42 barrels out of 100 barrels input.
Therefore, the amount of energy lost as waste heat = (100 - 42) barrels = 58 barrels.

Question 8

A gasoline engine absorbs 2 500 J of heat and performs 1 000 J of mechanical work in each cycle.The efficiency of the engine is

Accepted Answer

The answer of A gasoline engine absorbs 2 500 J...

Question 9

All real engines are less efficient than the Carnot engine because

Accepted Answer

The Carnot engine is the most efficient engine possible because it operates through a reversible cycle. This means that the engine can be run in both directions, allowing it to convert the maximum amount of heat energy into work. Real engines, on the other hand, operate through irreversible cycles, which makes them less efficient than the Carnot engine. Therefore, choice B is the best answer.

Question 10

An 800-MW electric power plant has an efficiency of 30%.It loses its waste heat in large cooling towers.Approximately how much waste heat (in MJ)is discharged to the atmosphere per second?

Accepted Answer

The plant's efficiency is given as 30% which means that 70% of the energy input is lost as waste heat. Therefore, the waste heat discharged to the atmosphere per second can be calculated as follows:

Waste heat = Energy input x (1 - Efficiency)
Waste heat = 800 MW x (1 - 0.30)
Waste heat = 560 MW

To convert MW to MJ, we need to multiply by the conversion factor of 3,600,000 (1 MW = 3,600,000 MJ/s):

Waste heat = 560 MW x 3,600,000 MJ/MW
Waste heat = 2,016,000,000 MJ/s

Therefore, the waste heat discharged to the atmosphere per second is approximately 1,900 MJ (rounded to the nearest hundred). The answer is B.

Question 11

By operating a reversible heat engine with an ideal gas as the working substance in a Carnot cycle and measuring the ratio Q_c/Q_h,we can calculate

Accepted Answer

The given ratio can be written as (QC/QH)(U1B0/U1B1cS1)(U1B1hS1/U1B0)(V_c/V_h)(P_c/P_h). Since Carnot cycle is a reversible cycle, the efficiencies of the engine are equal to (Qin - Qout)/Qin where Q is the heat absorbed/rejected and are proportional to the temperature differences of the heat reservoirs, and (U1 - U0)/Qin and (U1 - U0)/Qout where U is the internal energy of the gas. As a result, the ratio (QC/QH)(U1B0/U1B1cS1)(U1B1hS1/U1B0) is equal to the ratio (V_c/V_h)(P_c/P_h) and is dependent only on the temperature of the heat reservoirs, regardless of the nature of the working substance. Therefore, the only possible result that can be calculated from the given ratio is the ratio of the products of volumes and pressures, P_cV_c/P_hV_h.

Question 12

A heat pump has a coefficient of performance of 4.If the heat pump absorbs 20 cal of heat from the cold outdoors in each cycle,the heat expelled (in cal)to the warm indoors is

Accepted Answer

The answer of A heat pump has a coefficient of...

Question 13

Which of the following is an almost reversible process?

Accepted Answer

A slow isothermal compression of a gas can be almost reversible because the temperature is constant and the process is slow enough to maintain equilibrium. The other processes listed are irreversible, meaning they cannot be reversed without significant energy input or changes to the system.

Question 14

A homeowner has a new oil furnace which has an efficiency of 60%.For every 100 barrels of oil needed to heat his house,how much (in barrels of oil)goes up the chimney as waste heat?

Accepted Answer

If the furnace has an efficiency of 60%, it means that only 60% of the oil that is burned is converted into heat for the house. The remaining 40% of the oil is lost as waste heat, which goes up the chimney. Therefore, for every 100 barrels of oil used, 40 barrels are wasted as heat that goes up the chimney. Thus, the answer is C) 40.

Question 15

An engine is designed to obtain energy from the temperature gradient of the ocean.What is the thermodynamic efficiency of such an engine if the temperature of the surface of the water is 59 $\degree$F (15 $\degree$C)and the temperature well below the surface is 41 $\degree$F (5 $\degree$C)?

Accepted Answer

The thermodynamic efficiency of an engine operating between two temperatures is given by the Carnot efficiency formula: η = 1 - (Tc/Th), where Tc and Th are the absolute temperatures (in Kelvin) of the cold and hot reservoirs, respectively. Converting the given temperatures to Kelvin: Th = 15°C + 273.15 = 288.15 K, Tc = 5°C + 273.15 = 278.15 K. The efficiency is η = 1 - (278.15/288.15) ≈ 0.0347 or 3.5%.

Question 16

An adiabatic free expansion of a gas in a thermally isolated container is not reversible because

Accepted Answer

In an adiabatic free expansion, the gas does not exchange heat with its surroundings because the system is thermally isolated. However, to return the gas to its original volume, work must be done on it, which cannot be fully recovered due to the nature of the expansion being free (no external pressure applied against which the gas does work). This makes the process irreversible. Heat exchange (choice B) and a change in internal energy after returning to the original state (choice C) are not reasons for the irreversibility in this context.

Question 17

A gasoline engine absorbs 2 500 J of heat and performs 1 000 J of mechanical work in each cycle.The amount of heat expelled in each cycle is

Accepted Answer

According to the first law of thermodynamics, the heat absorbed by the engine (2,500 J) is equal to the sum of the mechanical work done (1,000 J) and the heat expelled. Therefore, the heat expelled in each cycle is 2,500 J - 1,000 J = 1,500 J, which is option B.

Question 18

An ideal heat engine can have an efficiency of 1 if the temperature of the low temperature reservoir is

Accepted Answer

According to the Carnot efficiency formula, the efficiency of a heat engine is given by 1 - (Tc/Th), where Tc is the temperature of the low temperature reservoir and Th is the temperature of the high temperature heat source. As efficiency cannot be greater than 1, Tc must be 0 K (absolute zero) to achieve a Carnot efficiency of 1.

Question 19

A company that produces pulsed gas heaters claims their efficiency is approximately 90%.If an engine operates between 250 $\degree$C and 25 $\degree$C,what is its maximum thermodynamic efficiency?

Accepted Answer

The Carnot efficiency equation is 1 - (Tc / Th), where Tc is the temperature of the cold reservoir and Th is the temperature of the hot reservoir. Converting the temperatures to Kelvin, we get a range of 298K to 523K. Plugging these values into the Carnot efficiency equation results in a maximum efficiency of 43%. Therefore, the pulsed gas heater's claimed efficiency of 90% cannot be matched by the engine.

Question 20

Which answer below is not a statement of the second law of thermodynamics?

Accepted Answer

Option D is not a statement of the second law of thermodynamics. It is related to the concept of reversible processes in theory. The other options (A,B,C, and E) all relate to the second law of thermodynamics.

Quiz 18: Heat Engines,entropy,and the Second Law of Thermodynamics

The thermal efficiency of a heat engine is given by

A steam engine is operating at its theoretical maximum efficiency of 60%.If the waste heat has a temperature of 100 $\degree$ F (38 $\degree$ C) ,what is the temperature of the boiler?

A lawn mower has a 6-horsepower engine (1 HP = 750 W) .If the engine has an efficiency of 20%,and the throttle is such that the engine cycles 10 times a second,the heat that is expelled in one cycle is

A refrigerator has a coefficient of performance of 4.If the refrigerator absorbs 30 cal of heat from the cold reservoir in each cycle,the heat expelled (in cal) into the heat reservoir is

A Carnot cycle,operating as a heat engine,consists,in the order given,of

An automobile engine operates with an overall efficiency of 12%.How much energy is delivered as waste heat (in gallons of gasoline) for each 10 gallons of fuel burned?

A new electric power plant has an efficiency of 42%.For every 100 barrels of oil needed to run the turbine,how many are essentially lost as waste heat (in barrels of oil) to the environment?

A gasoline engine absorbs 2 500 J of heat and performs 1 000 J of mechanical work in each cycle.The efficiency of the engine is

All real engines are less efficient than the Carnot engine because

An 800-MW electric power plant has an efficiency of 30%.It loses its waste heat in large cooling towers.Approximately how much waste heat (in MJ) is discharged to the atmosphere per second?

By operating a reversible heat engine with an ideal gas as the working substance in a Carnot cycle and measuring the ratio Q_c/Q_h,we can calculate

A heat pump has a coefficient of performance of 4.If the heat pump absorbs 20 cal of heat from the cold outdoors in each cycle,the heat expelled (in cal) to the warm indoors is

Which of the following is an almost reversible process?

A homeowner has a new oil furnace which has an efficiency of 60%.For every 100 barrels of oil needed to heat his house,how much (in barrels of oil) goes up the chimney as waste heat?

An engine is designed to obtain energy from the temperature gradient of the ocean.What is the thermodynamic efficiency of such an engine if the temperature of the surface of the water is 59 $\degree$ F (15 $\degree$ C) and the temperature well below the surface is 41 $\degree$ F (5 $\degree$ C) ?

An adiabatic free expansion of a gas in a thermally isolated container is not reversible because

A gasoline engine absorbs 2 500 J of heat and performs 1 000 J of mechanical work in each cycle.The amount of heat expelled in each cycle is

An ideal heat engine can have an efficiency of 1 if the temperature of the low temperature reservoir is

A company that produces pulsed gas heaters claims their efficiency is approximately 90%.If an engine operates between 250 $\degree$ C and 25 $\degree$ C,what is its maximum thermodynamic efficiency?

Which answer below is not a statement of the second law of thermodynamics?

Quiz 18: Heat Engines,entropy,and the Second Law of Thermodynamics

The thermal efficiency of a heat engine is given by

A steam engine is operating at its theoretical maximum efficiency of 60%.If the waste heat has a temperature of 100 °\degree° F (38 °\degree° C) ,what is the temperature of the boiler?

A lawn mower has a 6-horsepower engine (1 HP = 750 W) .If the engine has an efficiency of 20%,and the throttle is such that the engine cycles 10 times a second,the heat that is expelled in one cycle is

A refrigerator has a coefficient of performance of 4.If the refrigerator absorbs 30 cal of heat from the cold reservoir in each cycle,the heat expelled (in cal) into the heat reservoir is

A Carnot cycle,operating as a heat engine,consists,in the order given,of

An automobile engine operates with an overall efficiency of 12%.How much energy is delivered as waste heat (in gallons of gasoline) for each 10 gallons of fuel burned?

A new electric power plant has an efficiency of 42%.For every 100 barrels of oil needed to run the turbine,how many are essentially lost as waste heat (in barrels of oil) to the environment?

A gasoline engine absorbs 2 500 J of heat and performs 1 000 J of mechanical work in each cycle.The efficiency of the engine is

All real engines are less efficient than the Carnot engine because

An 800-MW electric power plant has an efficiency of 30%.It loses its waste heat in large cooling towers.Approximately how much waste heat (in MJ) is discharged to the atmosphere per second?

By operating a reversible heat engine with an ideal gas as the working substance in a Carnot cycle and measuring the ratio Qc/Qh,we can calculate

A heat pump has a coefficient of performance of 4.If the heat pump absorbs 20 cal of heat from the cold outdoors in each cycle,the heat expelled (in cal) to the warm indoors is

Which of the following is an almost reversible process?

A homeowner has a new oil furnace which has an efficiency of 60%.For every 100 barrels of oil needed to heat his house,how much (in barrels of oil) goes up the chimney as waste heat?

An adiabatic free expansion of a gas in a thermally isolated container is not reversible because

A gasoline engine absorbs 2 500 J of heat and performs 1 000 J of mechanical work in each cycle.The amount of heat expelled in each cycle is

An ideal heat engine can have an efficiency of 1 if the temperature of the low temperature reservoir is

A company that produces pulsed gas heaters claims their efficiency is approximately 90%.If an engine operates between 250 °\degree° C and 25 °\degree° C,what is its maximum thermodynamic efficiency?

Which answer below is not a statement of the second law of thermodynamics?

A steam engine is operating at its theoretical maximum efficiency of 60%.If the waste heat has a temperature of 100 $\degree$ F (38 $\degree$ C) ,what is the temperature of the boiler?

By operating a reversible heat engine with an ideal gas as the working substance in a Carnot cycle and measuring the ratio Q_c/Q_h,we can calculate

A company that produces pulsed gas heaters claims their efficiency is approximately 90%.If an engine operates between 250 $\degree$ C and 25 $\degree$ C,what is its maximum thermodynamic efficiency?