Heat and Thermodynamics II - SS1 Physics Past Questions and Answers - page 5
The efficiency of a heat engine can be improved by:
Increasing the temperature of the heat sink
Increasing the temperature of the heat source
Decreasing the temperature difference between the heat source and the heat sink
Increasing the size of the engine
Which type of heat engine has the highest theoretical efficiency?
Carnot engine
Stirling engine
Diesel engine
Steam engine
In a heat engine, the net work output is equal to:
Heat input minus heat output
Heat output minus heat input
Heat input divided by heat output
Heat output divided by heat input
A heat engine receives 500 J of heat energy from a high-temperature source and releases 300 J of heat energy to a low-temperature sink. What is the efficiency of the heat engine?
Efficiency = (Work output / Heat input) x 100%
Work output = Heat input - Heat output
Work output = 500 J - 300 J = 200 J
Efficiency = (200 J / 500 J) x 100% = 40%
A heat engine has an efficiency of 25% and releases 400 J of heat energy to a low-temperature sink. How much work is done by the engine?
Efficiency = (Work output / Heat input) x 100%
Work output = Efficiency x Heat input
25% = Work output / (Heat input - 400 J)
Work output = 0.25 x (Heat input - 400 J)
Work output = 0.25 x Heat input - 100 J
Heat input - 100 J = 400 J
Heat input = 500 J
Work output = 0.25 x 500 J - 100 J = 25 J
A Carnot engine operates between a high-temperature reservoir at 400 K and a low-temperature reservoir at 100 K. The heat input to the engine is 800 J. What is the heat output of the engine?
Carnot efficiency = 1 - (Tlow / Thigh)
Carnot efficiency = 1 - (100 K / 400 K) = 0.75
Heat output = (1 - Carnot efficiency) x Heat input
Heat output = (1 - 0.75) x 800 J = 0.25 x 800 J = 200 J
An ideal heat engine has an efficiency of 60% and produces 400 J of work output. What is the heat input to the engine?
Efficiency = (Work output / Heat input) x 100%
60% = 400 J / Heat input
Heat input = 400 J / 0.6 = 666.67 J
A heat engine receives 800 J of heat energy from a high-temperature source and has an efficiency of 50%. How much work is done by the engine?
Efficiency = (Work output / Heat input) x 100%
Work output = Efficiency x Heat input
Work output = 0.5 x 800 J = 400 J
Which of the following is a primary function of a refrigeration system?
Cooling down a room
Generating electricity
Heating a room
Removing heat from a refrigerated space
In a refrigeration system, the working substance that absorbs heat from the refrigerated space is called:
Refrigerant
Compressor
Condenser
Evaporator