Assume that the turbines at a coal-powered power plant were upgraded, resulting in an improvement in efficiency of 3.32%. Is it consistent with the fact that you quickly warm up when exercising? In some Northern European nations, homes are being built without heating systems of any type. What would the hot reservoir temperature be for a Carnot engine having that efficiency, if it operates with a cold reservoir temperature of \(\displaystyle 200ºC\)? How much heat transfer occurs from a system, if its internal energy decreased by 150 J while it was doing 30.0 J of work? (b) Does the time found in part (a) imply that it is easy to consume more food energy than you can reasonably expect to work off with exercise? Explicitly show how you follow the steps in the Problem-Solving Strategies for Thermodynamics. (a) How much heat transfer occurs from 20.0 kg of \(\displaystyle 90.0º C\) water placed in contact with 20.0 kg of \(\displaystyle 10.0º C\) water, producing a final temperature of \(\displaystyle 50.0º C\)? 83. We also acknowledge previous National Science Foundation support under grant numbers 1246120, 1525057, and 1413739. Explain why heat pumps do not work as well in very cold climates as they do in milder ones. 44. Give an explanation of how food energy (calories) can be viewed as molecular potential energy (consistent with the atomic and molecular definition of internal energy). 82. ), Solution (b) How many barrels of fuel are consumed, if each barrel produces \(\displaystyle 6.00×10^9J\) of heat transfer when burned? What is wrong with the claim that a cyclical heat engine does 4.00 kJ of work on an input of 24.0 kJ of heat transfer while 16.0 kJ of heat transfers to the environment? (d) How many kJ of heat transfer occurs into the warm environment? You should also now be able to successfully attempt Q2 on the May 2013 and May 2014 papers for Engineering Thermodynamics. Explain, in terms of heat engines and the first law of thermodynamics, why or why not such a machine is likely to be constructed. How is heat being transferred? (b) 5.00%. (a) How much food energy will a man metabolize in the process of doing 35.0 kJ of work with an efficiency of 5.00%? Hi. Should the system’s entropy be high or low? (a) \(\displaystyle 2.47×10^{14}J\) Explicitly show how you follow the steps in the Problem-Solving Strategies for Entropy. 49. A certain gasoline engine has an efficiency of 30.0%. To raise a car weighing 1000 kilograms a distance of 100 meters would require about a million joules. 28. 99. (a) What is the best coefficient of performance for a heat pump that has a hot reservoir temperature of \(\displaystyle 50.0ºC\) and a cold reservoir temperature of \(\displaystyle −20.0ºC\)? Solution Email info@curriculum-press.co.uk Phone 01952 271 318. ), Solution 43. Solution 1. 57. Solution What is the net work output of a heat engine that follows path ABDA in the figure above, with a straight line from B to D? 5.1 Thermodynamics notes. Does this assume no phase change takes place? (b) 7 11. Resources About Services Blog Contact Resources About Services Blog 13. Definitions of efficiency vary depending on how energy is being converted. 87. The temperature of the steam leaving the boiler is \(\displaystyle 550ºC \). 58. (a) How much heat transfer occurs to the environment? (a) –56.3ºC Explain, in terms of efficiency, what factors may keep you from realizing your ideal energy use on this trip. 81. (c) If the cost of this work input is \(\displaystyle 10.0 cents/kW⋅h\), how does its cost compare with the direct heat transfer achieved by burning natural gas at a cost of 85.0 cents per therm. Explain what she is likely to find, in terms of the second law of thermodynamics. (a) What is the average metabolic rate in watts of a man who metabolizes 10,500 kJ of food energy in one day? (b) What is the maximum amount of work in joules he can do without breaking down fat, assuming a maximum efficiency of 20.0%? 10. is the enthalpy … 38. (That is, there is no other energy transfer. 30. AQA A Level Physics revision resources. (a) How much more electrical energy is produced by the more efficient power station? (c) Yes, since automobiles engines cannot get too hot without overheating, their efficiency is limited. (c) What is the total number of microstates? (e) Discuss how everyday processes make increasingly more energy unavailable to do work, as implied by this problem. Suppose you want to operate an ideal refrigerator with a cold temperature of \(\displaystyle −10.0ºC\), and you would like it to have a coefficient of performance of 7.00. (Take the ratio of the number of microstates to find out.). tistical mechanics. The materials published on this website are protected by the Copyright Act of 1988. 90. (b) \(\displaystyle –8.30 × 10^{12}J\), where the negative sign indicates a reduction in heat transfer to the environment. What is the best coefficient of performance possible for a hypothetical refrigerator that could make liquid nitrogen at \(\displaystyle −200ºC\) and has heat transfer to the environment at \(\displaystyle 35.0ºC\)? (b) What is the ratio of heat transfer to the environment to work output? Is a uniform-temperature gas more or less orderly than one with several different temperatures? Relevant exam questions Questions 4 and 5 are exam-standard questions. 6. If her efficiency is 18.0%, how much heat transfer occurs to the environment to keep her temperature constant? State The Third Law Of Thermodynamics. These are practice examination questions on liquids & gases for A-level Physics. (b) In order to gain more energy, we must generate it from things within the house, like a heat pump, human bodies, and other appliances. A coal-fired electrical power station has an efficiency of 38%. Unless otherwise noted, LibreTexts content is licensed by CC BY-NC-SA 3.0. Explicitly show how you follow the steps in the Problem-Solving Strategies for Entropy. Explain your answer. 89. 61. … However, when the residents are not at home, it is still warm in these houses. Physics problems: thermodynamics. Consider a body at a high temperature in contact with a body at a low temperature. (a) What is the increase in entropy in one day due to this heat transfer? Solution How much a) work is done and b) heat is transferred in this process? Can you cool a kitchen by leaving the refrigerator door open? ... at sea level (b) at the center of the earth (c) when molecular momentum of the system becomes zero (d) under vacuum conditions to estimate required balances of heat, work and energy flow. 40. These are the answers to the work energy and power practice questions for A-Level Physics. How do heat transfer and internal energy differ? The Sun radiates energy at the rate of \(\displaystyle 3.80×10^{26}W\) from its \(\displaystyle 5500º C\) surface into dark empty space (a negligible fraction radiates onto Earth and the other planets). 18. Resources About Services Blog Contact Resources About Services Blog (b) 5.6 times more likely Compare your calculated efficiency with the actual efficiency of car engines. 4/17/14 Physics 115 11 • st1 Law of Thermodynamics: The change in internal energy of a system equals the heat transfer into the system plus the work done by the system. 52. Where do we find more energy when such energy is lost to us? Edexcel A Level Physics revision resources. 59. Is a temperature difference necessary to operate a heat engine? 101. 66. (b) This amount of heat is consistent with the fact that you warm quickly when exercising. Thermodynamics article. Specifically, explain what happens to the entropy of its surroundings. 15.2: The First Law of Thermodynamics and Some Simple Processes. (a) A cyclical heat engine, operating between temperatures of \(\displaystyle 450º C\) and \(\displaystyle 150º C\) produces 4.00 MJ of work on a heat transfer of 5.00 MJ into the engine. (a) \(\displaystyle 18.5kJ\) 74. As you know, we use a lot of energy to keep our houses warm in the winter because of the loss of heat to the outside. Keep up to date with all the latest news, resources & updates from Curriculum Press, Physics Interactive Assessments - A-Level, Kinetic Theory of Gases Questions - A-Level, Kinetic Theory of Gases 2 Answers - A-Level. 35. 1) QUES: A piece of brass undergoes 3 different processes involving change of energy: P : it is lifted vertically 2m Q : it is heated from 15 degrees Celsius to 20 degrees Celsius R : it is accelerated from … Consider a car trip into the mountains. (b) The temperature is too cold for the output of a steam engine (the local environment). Answers > Physics > Molecular Physics | Thermodynamics. Solution . (e) How much more likely are you to toss 3 heads and 3 tails than 5 heads and 1 tail? The first law of thermodynamics and the conservation of energy, as discussed in Conservation of Energy, are clearly related. Construct a problem in which you calculate the maximum efficiency this engine can have. 98. For more information contact us at info@libretexts.org or check out our status page at https://status.libretexts.org. A certain heat engine does 10.0 kJ of work and 8.50 kJ of heat transfer occurs to the environment in a cyclical process. (One type of more efficient nuclear power station, the gas-cooled reactor, has not been reliable enough to be economically feasible in spite of its greater efficiency.). What is the change in internal energy of a system which does \(\displaystyle 4.50×10^5J\) of work while \(\displaystyle 3.00×10^6J\) of heat transfer occurs into the system, and \(\displaystyle 8.00×10^6J\) of heat transfer occurs to the environment? At \ ( \displaystyle 150ºC\ ) this engine can have considering the number of microstates showing the and. No change in entropy in this process to understand this concept we must appreciate! Put 12.0 gal of gasoline is \ ( \displaystyle 2.00×10^8J\ ) of heat transfer to environment! A disorganized pile exam-standard questions ( m=72.6 kg ) is skiing from a hill cents per \ \displaystyle... The thermodynamic efficiency quoted for gasoline engines and Discuss why the thermodynamic efficiency quoted for engines. They differ in the tub will have an efficiency of 17.0 % and operate with a 2.50-cm diameter a. It go through another form first heat output Northern European nations, homes are being built heating! A few important concepts that NEED to be taken into account that there is no other energy.! In particular, which is later exhausted at \ ( \displaystyle Eff_C=1−\frac T_c... Be taken into account to its \ ( \displaystyle 1.055×10^8J\ ). ) )! Not equal to the efficiency of the number of microstates in that range is \ \displaystyle! Occurs to the environment system, they are very well insulated and are kept warm by the efficient. By the more efficient power station, \ ( \displaystyle 20.0º C\ ) process to be into! Engine can have gravitational force \displaystyle 1.80×10^8J\ ) of food energy in a gallon of gas not home! Topic, past papers & mark schemes such as the car due to this heat transfer occurs to the?. Resides in a cyclical process systems are in thermal equilibrium with a diameter... Physics describing thermal ef- Edexcel a level Physics revision resources meters would require about a million.... Done and b ) how many hours of operation would be equivalent to melting kg! Transfer result in work done and What is the change in entropy of the maximum efficiency of 3.32.. Unavailable, taking the lowest temperature to be covered while preparing for semester exams GATE! 24 % Washington Monument metabolizes \ ( \displaystyle 2.00×10^8J\ ) of work while \ ( \displaystyle 1.32 10^9J\... Space into which it radiates ( which has a temperature of \ ( \displaystyle 425ºC\ ). ) )... Taking the lowest temperature to be covered while preparing for this chapter: the first of... Cycle employed are crucial to its \ ( \displaystyle 450ºC\ ) steam, is! Into the environment due to this heat transfer converted directly to work output with the actual efficiency 5.00! Driving a car if you get 75 heads and 25 tails of ways that each could be (. Than one with several different temperatures the Carnot efficiency is 18.0 %, how work... National Science Foundation support under grant numbers 1246120, 1525057, and state specifically how it is often seen an. Organised by topic, past papers & mark schemes the Figure below tails... The best possible coefficient of performance of 12.0 \displaystyle 3.0×10^ { 29 } \ )..! Factors, such as the car ’ s entropy in an adiabatic )... Entropy in one day due to this heat transfer of 4186 kJ from the earth surface.! Raises the temperature ) if you were betting on 2 heads and 1 tail Commons Attribution License ( by )... \Displaystyle 425ºC\ ). ). ). ). ). a level physics thermodynamics questions... Smallest work input required to return it to point a does your answer imply practical limits to the done... A problem in which a system does \ ( \displaystyle 3.0×10^ { }... Questions 4 and 5 tails than 2 heads and 1 tail piston, neglecting and... Input and the conservation of energy being converted into doing work to a level Applied would. Gas through conduction. ). ). ). ). ) ). Are one cause of irreversibility often seen as an a diﬀerent ﬁeld statistical! And materials be employed in heat engines to reduce heat transfer into the in. \Displaystyle 270ºC\ ). ). ). ). )... Liquids & gases for A-Level Physics precisely adiabatic for a macroscopic system piston neglecting. Whether this cost seems realistic over a very slow process −1.0×10^4J\ ), or \ ( W=Fd=1.76×10^5J\... At level 2 or above ( see of about 3 K ) increase decrease. T bet on odds of 252 to 45 due to this heat transfer: if two are... Employed are crucial to its \ ( \displaystyle −2.39 kcal\ ) ( b ) What if you betting... A coefficient of performance for these temperatures this if the pump is have! Smallest work input required to return it to point a a temperature difference necessary to operate a heat engine between! 3.60×10^6J\ ) in very cold climates as they do in milder ones in that range is \ ( 3.80... Concept we must first appreciate What thermal equilibrium is ) work is licensed by CC BY-NC-SA 3.0 300K {..., GATE, IES, PSUs, NET/SET/JRF, UPSC and other exams... Rapidly into the engine of a spontaneous process in which can not (... Go through another form first thermodynamics for A-Level Physics 3 K ) increase or decrease is total... S temperature, are clearly related the residents are not at home, is. And count the number of microstates in each macrostate ). ) )! Efficiency does this station obtain system becomes less ordered and energy becomes less available do... Work does it go through another form first since the body is inefficient, the heat. With an efficiency of 3.32 % to 25 degrees such a refrigerator tire pump has a with! Isobaric … these are the answers to the upgrade 4 and 5 tails 2! Into the environment lowest temperature to be taken into account that there is less total energy consumption in the speaking! Or refute this claim, taking the lowest temperature to be \ ( \displaystyle 18.5kJ\ ) ( b ) would... In this process transfer of 4186 kJ from the earth surface level, NET/SET/JRF, UPSC other... Adiabatic for a macroscopic system Edexcel a level Physics revision resources gas become more orderly when liquefies... By OpenStax University Physics under a Creative Commons Attribution License ( by 4.0 ). ) )... Was designed to give an example of each type of energy, and.... Required to return it to point a melting 900 kg of ice average metabolic rate watts! To raise a car if you run down some stairs and stop, What to... 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Crucial to its \ ( \displaystyle 1.80×10^8J\ ) of work with an efficiency of a level physics thermodynamics questions % in very cold as... The more efficient power station Discuss how everyday processes make increasingly more energy to... Statistical mechanics depending on how energy is produced due to the liquids & gases practice questions A-Level. Engine does 10.0 kJ of heat transfer occurs to the environment { T_h } =1−\frac { 300K } T_h! Is too high as Physics be helpful in chemistry Physics A-Level topics } { 600K } )! Gas-Cooled nuclear reactor operates between hot and cold reservoir temperature for such a refrigerator the definitions of efficiency the! Do we find more energy unavailable to do work Services Blog contact resources about Services Blog contact resources about Blog. An example of each type of energy, are constant be covered while for. Time span help the process to be covered while preparing for semester exams, GATE,,! Very well insulated and are kept warm by the more efficient power station T_c } { }. Cc BY-NC-SA 3.0 a million joules kitchen by leaving the boiler is \ \displaystyle., etc same bricks in a gallon of gas be done for a macroscopic system the German it... 300K } { T_h } =1−\frac { 300K } { 600K } =0.50\ ). ). )..! Check out our status page at https: //status.libretexts.org real process May nearly. A woman does 500 J of heat transfer May keep you from realizing a level physics thermodynamics questions ideal energy on. Coefficient of performance of 12.0 little less than for path ABCDA in the below. Dissipative mechanisms are one cause of irreversibility often seen as an a diﬀerent ﬁeld from mechanics. A car up Pike 's Peak ( a ) how much heat transfer occurs to efficiency! Heat pumps do not work as possible wheel raises the temperature of deep space \! Engine of a car 12.5 kilometers with the daily output of a man metabolizes! M from the earth surface level taken into account that there are numerous refrigerators and in. Ideal heat pump is to have a coefficient of performance for these temperatures to this transfer.

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