quiz lesson 3

Engine is 1010oc and the exhaust is

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Unformatted text preview: ) x 100 Thot = 1071 + 273 = 1344 K Tcold = 187 + 273 = 460 K Carnot's Efficiency = (1 - (460 / 1344)) x 100 = 65.77% The useful output from a heat engine is 230 cal. The energy that is wasted is 5672 J? What is the Carnot efficiency (maximum efficiency) of the engine? Correct A ) 14.55% Efficiency = ((useful energy output) / (useful energy output + waste energy output))*100. Note: Use units consistently. 1 Cal = 4.2 J Efficiency = (230 x 4.2) / [(230 x 4.2) + 5672] = 0.1455 = 14.55% The flame temperature in an automobile engine is 1118oC, and the exhaust is emitted at 128oC. What is the maximum possible efficiency of this engine in percentage? Correct A ) 71.2 Carnot's Efficiency = (1 - (Tcold / Thot)) x 100 Thot = 1118 + 273 = 1391 K Tcold = 128 + 273 = 401 K Carnot's Efficiency = (1 - (401 / 1391)) x 100 = 71.17% Which one of the following is a list of devices from least efficient to most efficient? Correct D ) Light- Bulb, Automobile Engine, Power Plant, Electric Motor Incandescent Light- Bulb (5%), Fluorescent Light- Bulb (20%), Electric Motor (90%), Power Plant (35%), Automobile Engine (25%), Home oil Furnace (80%) The useful output from a heat engine is 232 cal. The energy that is wasted is 5691 J? What is the Carnot efficiency (maximum efficiency) of the engine? Correct A ) 14.62% Efficiency = ((useful energy output) / (useful energy output + waste energy output))*100. Note: Use units consistently. 1 Cal = 4.2 J Efficiency = (232 x 4.2) / [(232 x 4.2) + 5691] = 0.1462 = 14.62% What is the form of useful energy output in the case of a TV? Correct A ) Radiation A TV converts electrical energy into radiation (the pictures that we see). Which one of the following energy conversion devices has the lowest energy efficiency? Correct C ) Incandescent light bulb Incandescent light bulb has an efficiency of 5%, Fluorescent light bulb has an efficiency of 20%, Steam boiler in a power plant has an efficiency of 88% and Electric motor has an efficiency of 90% If the energy input of a system is 87 calories and its output is 69 calories, what is the efficiency of the system? Correct B ) 0.7931 System Efficiency = 69 / 87 = 0.7931 = 79.31% 12 million Joules of chemical energy are supplied to a boiler in a power plant. 8 x 10^6 Joules of energy are lost through unburnt fuel. The boiler radiates 1.8 million Joules to the atmosphere. What is the efficiency of the boiler in percentage? Correct A ) 18.3 Energy efficiency = Useful energy output / Total energy input Useful energy output = 12 - 8 - 1.8 = 2.2 million Joules Efficiency of the boiler = 2.2 / 12 x 100 = 18.33% Carnot efficiency is the efficiency of a heat engine....
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