What is Efficiency: Definition and 947 Discussions

Efficiency is the (often measurable) ability to avoid wasting materials, energy, efforts, money, and time in doing something or in producing a desired result. In a more general sense, it is the ability to do things well, successfully, and without waste. "Efficiency is thus not a goal in itself. It is not something we want for its own sake, but rather because it helps us attain more of the things we value". In more mathematical or scientific terms, signifies the level of performance that uses the least amount of inputs to achieve the highest amount of output. It often specifically comprises the capability of a specific application of effort to produce a specific outcome with a minimum amount or quantity of waste, expense, or unnecessary effort. Efficiency refers to very different inputs and outputs in different fields and industries.

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  1. T

    Understanding Solar Cell Efficiency and Production: What You Need to Know

    Hey, I recently read that they made a 40% efficient solar cell... what does this actually mean? How do they calculate this efficiency... and how much power do these cells actually produce? and what's with the mono and poly crystalline titles that they get? what does that mean?? Any info...
  2. mbrmbrg

    AZINGWhat is the efficiency of this thermodynamic cycle?

    Homework Statement Suppose 1.0 mol of a monatomic ideal gas initially at 10L and 302K is heated at constant volume to 604K, allowed to expand isothermally to its initial pressure, and finally compressed at constant pressure to its original volume, pressure, and temperature. (c)What is the...
  3. H

    Motor Efficiency: Increase in Voltage & Why?

    for my A level coursework i am doing the efficieny of a motor, I've just about sussed the theory:confused: . Now i have found out that the efficieny increases as the voltage increases and its wrong! :mad: i need help on saying why this would be the case. help would be much appreciated!
  4. B

    How Does Blade Number and Wind Speed Affect Wind Turbine Efficiency?

    I'm doing an experiment (at A-Level) to see the efficiency of a wind turbine. I'm doing this by changing the number of blades and varying the wind speeds. I wondered if anyone had an equation that could look at efficiency? I have the current and the voltage (and wind speed). Sorry if I've...
  5. A

    Efficiency of an elastic band. Hooke's Law

    Homework Statement I am doing a lab experiment and the objective is to find the efficiency of an elastic band. Distance to ceiling=2.9m Mass of elastic band= 1.85g Force 2.6N (found using Newton meter) Extension: 6.4cm Homework Equations Well I am not looking for a solution, I...
  6. Chi Meson

    Is Solar Water Heating Cost-Effective in Cold Climates?

    I'm very excited. I just finished ordering all the necessary parts to install a solar water heating system. With the likelihood of electricity only getting more expensive, coupled with the likelihood of my 3 children getting bigger, It seemed like a no-brainer. Who else has solar heat...
  7. adrenaline

    Negative Efficiency: Is Human Motion Worth It?

    strange question efficiency if a human does pushups , it is an oscillatory motion and no work was done. efficiency which is defined as e= useful energy output/energy input is 0. But since you burn a lot of atp and calories, can the efficiency coefficient be a negative value?
  8. T

    Do light bulbs or convection heaters heat a room with the highest efficiency?

    There's a debate these days related to the australian ban of traditional light bulbs, because of the loss of heat energy: http://www.ens-newswire.com/ens/feb2007/2007-02-21-01.asp" But in a colder place than Australia (like Norway), it think this number would be lower than 66% because some of...
  9. P

    Efficiency: Work, Limits, and Zeno's Paradoxes

    I think the 2nd law of thermodynamics, which places limits on the efficiency of thermal engines, can also be interpreted as saying increasing efforts to improve efficiency result in geometrically decreasing results. I can't find that stated, though. I suppose it's just the first derivative...
  10. L

    What Factors Affect the Efficiency of a Siphon?

    (Hope this is in the right forum) For my A Level coursework I have to do a practical investigation. I'm thinking of doing one looking at the efficiency of a siphon. One relationship I am going to be looking at is the rate of flow vs height (difference between the two water levels). Now...
  11. T

    Gain 100% Efficiency - Exploring Heating Elements

    (ok i not sure where this topic goes so ill take a guess its here) ok, I hear that nothing is 100% efficienct. some energy is always lost as heat and sound. however, what about heating elements? or electrical heats or whatever, surely the lost heat (and i don't think any sound cause its...
  12. K

    Another heat engine efficiency problem

    A reversible heat engine has an efficiency of 34.2%, removing heat from a hot reservoir and rejecting heat to a cold reservoir at 0°C. If the engine now operates in reverse, how long would it take to freeze 1.10 kg of water at 0°C, if it operates on a power of 183 W? I am getting stuck...
  13. K

    Calculate Engine Efficiency: 0.490 kJ of Heat for 0.120 kJ of Work

    An engine releases 0.490 kJ of heat for every 0.120 kJ of work it does. What is the efficiency of the engine? I am having trouble with this problem. I tried Wnet/ heat input = efficiency 0.120/0.450 = 0.27 but it says it is the wrong answer. (correct answer is 0.21)
  14. M

    How High Can a Motor Lift a Mass Using a Charged Capacitor?

    Homework Statement A 0.45 µF capacitor is charged by a 1.5 V battery. After being charged, the capacitor is connected to a small electric motor. Assuming 100% efficiency, to what height can the motor lift a 4.7 g mass? Homework Equations I really need some direction to start off this...
  15. S

    Toy Propeller Efficiency: Range of Efficiencies

    Question: what is the range for propeller efficiency for plastic toy propellers?
  16. S

    Possible webpage title: What Type of Simple Machine Has an Efficiency of 81.7%?

    Homework Statement Could I please have a tutor check my answer and solution? question: An effort of 3 kN is required to move a mass of 2000 kg in a certain simple machine. If the mass is raised 1.5 meters while the effort moves 12 meters, find the efficiency? [b]2...
  17. 5

    Understanding Volumetric Efficiency and Beyond 100%

    First off I want to say thanks to all of those who help begineers like me out on this board...but anyways...:cool: In lamens terms, what is volumetric effeciency...how can one go above and beyond 100%. I was asking, because I looked at a dyno graph of a higher revving 302 (8,000 rpm)...
  18. T

    Solve Trebuchet Efficiency Mystery

    Homework Statement I've calculated the time, the distance, the height of the counterweight before launch, the mass/weight, and I need to calculate the energy efficiency. How to go about it? h = 0.71 m m = 1.445 kg g = 9.8 m/s^2 t = 0.7 s x = 4.44 m Homework Equations Eg = mgh Vix = x/t y =...
  19. B

    Solving a Group Job Efficiency Problem

    Suppose it takes 48 women 16 days to do the same job that it takes 16 men to do in 24 days. If 10 men started working on the job and worked for 5 hours, then all 48 women joined them. how long would it take them working together to finish the job? i know i have to find the rates so i have...
  20. E

    How do you calculate the net efficiency of a series of heat engines?

    Homework Statement Suppose that two heat engines are connected in a series, such that the heat exhaust of the first engine is used as the heat input of the second (attached diagram below). The efficiencies of the engines are e1 and e2, respectively. Show that the net efficiency of the...
  21. M

    What Is the Maximum Efficiency of a Heat Engine Using Lake Water Temperatures?

    Homework Statement Calculate the maximum possible efficiency of a heat engine that uses surface lake water at 18.5°C as a source of heat and rejects waste heat to the water 0.100 km below the surface where the temperature is 4.3°C. Homework Equations e=1-Qc/Qh Q=cm(deltaT) The...
  22. M

    Calculate its efficiency homework

    A 100-hp car engine operates at about 15 percent efficiency. assume that the engine's water temperature is 85deg C is its cold-temperature (exhaust) reservoir and 500deg C is its thermal "intake" temperature (the temperature of the exploding gas/air mixture) a)calculate its efficiency...
  23. M

    Photodetection Efficiency (pde)

    what is pde ? in terms of the formula , and in general so i can picture it in my mind so to speak.
  24. J

    Increase efficiency of rotating shaft.

    Here I describe one mechanical engineering situation that is very useful in any kind of mechanical and energy consumed industries.I hope you will try to understand it and use it. If you find any difficulty to understand ,feel free to ask me. we can increase efficiency of rotating shaft...
  25. T

    Efficiency Losses in a Reciprocating Engine

    We are developing an engine with pistons and cylinders that do not reciprocate... in other words the inertia of the pistons is constant at a given engine speed. More on that latter if you wish. We are looking for a method to calculate the efficiency losses in a conventional internal...
  26. S

    Nuclear power plant at 34% efficiency - rising temperature of water

    A nuclear power plant generates 500MW at 34 percent efficiency. The waste heat goes into the connecticut river with an average flow of 3x10 to the 4th kg/s. How much does the water temperature rise? (it requires 4.8x10 to the 3 to raise the temperature of 1kg of water 1K
  27. A

    Mechanical efficiency of IC engine

    what is the equation for the mechanical efficiency of an internal combustion engine? what are the formulas for 'ip' for 4-stroke and 2-stroke engines? thank you
  28. H

    What is the formula for calculating pump power and efficiency?

    Hi all! How do we define the power of a pump? I read a formula from a book which defines the power of the pump as follows: Power of the pump = Maximum back pressure * maximum flow rate / 2 Can anyone explain why the right hand side equals the left hand side? I don't understand why the...
  29. ?

    Thermodynamis - oil pump efficiency?

    Hi guys, could someone help me on this? I'm stuck :( *A motor draws 35kW electricity, it operates at 90% efficiency. The motor is connected to an oil pump which has an inlet diameter of 8cm & an outlet diameter of 12cm. pressure rise in the oil pump is 400kPa. oil enters the pump at 0.1m^3/s...
  30. ?

    Thermodynamics oil pump efficiency question

    Hi guys, could someone help me on this? I'm stuck :( *A motor draws 35kW electricity, it operates at 90% efficiency. The motor is connected to an oil pump which has an inlet diameter of 8cm & an outlet diameter of 12cm. pressure rise in the oil pump is 400kPa. oil enters the pump at 0.1m^3/s...
  31. I

    Average thermodynamic efficiency

    Appreciated members of this forum: Suppose we have an infinite set of n carnot cycles and we know the efficiency of each cycle of the set: E1,E2,E3,E4,E5,,,,,En , where En is the efficiency of the nth cycle. E1= 1-Ta/Tb1 , E2= 1-Ta/Tb2, E3= 1-Ta/Tb ... En=1-Ta/ Tbn Ta is the...
  32. S

    Annealing effect on PL efficiency

    I've some ZnO films grown on sapphire substrate. The ZnO film, however, is a highly-oriented polycrystalline film. The annealing was carried out at 800'C at different ambient, (N2, O2, etc.) After annealing, as expected, the crystallinity improved (narrowing FWHM of XRD). Resistivity...
  33. B

    What is the efficiency of the engine?

    f an engine must do 500 joules of work to pull a 10 kg load up to a height of 4 meters, what is the efficiency of the engine? So that's 400/50,000 which gives me 0.008 Does that mean the efficiency is 8%?
  34. N

    Thermodynamics - efficiency question

    The burning of gasoline in a car releases about 3.0 x 10^4 kcal/gal. If a car averages 41 km/gal when driving 90 km/h, which requires 25 hp, what is the efficiency of the engine under those conditions? I think I have an answer, but I'm not sure if it's correct. 1 horsepower = 746 watts...
  35. T

    Motor Efficiency: Understand Why 0.85 Matters

    In an assigment I'm using the general formula P=F*v, where P is the effect of a motor. The motor drives something through a series of sprockets, who's efficiency is 85 %, and so it seems intuitive to me to multiply the resulting P with 0,85 to get true effect, but apparently the solution divides...
  36. Pengwuino

    Efficiency of Eating Grass & Produce to Reach 2000kcal Daily

    I've always heard (from professionals as well) that each step in a food change has a roughly 10% efficiency rate. That is, you earn 10% of the energy the lower chain animal/plant earned when it ate/did whatever. Now my question is in regards to what you hear a lot of hippie-types say: Humans...
  37. D

    Does the Efficiency of Pulley Systems Increase with More Pulleys?

    It was my logic that efficiency should decrease as the amount of pulleys introduced into a pulley arrangement increased. This is since the amount of places where frictional resistance can occur is greater. Therefore, as TMA increases, i would expect Efficiency (AMA/TMA) to decrease...
  38. E

    Increase Carnot Efficiency: Lower Low-Temp Res?

    Suppose you had the choice of either raising the high-temperature reservoir a certain number of kelvins, or lowering the low-temperature reservoir the same number of kelvins. Which would you choose (assuming you wanted to increase the efficiency, of course)? After doing experimenting with...
  39. A

    High Temperature Superconductor Motors - Availability, Efficiency & More

    please help me in cllecting information about High Temperature Superconductor motor. Are they available in the market? how effecient are they? I need to know all their details, properties, design, advanteges. Thanks all
  40. russ_watters

    Federal A/C Unit Efficiency Standard Up

    I was looking through product info this morning and noticed (it got no press that I saw) that the DOE, after a protracted battle with the HVAC industry, started enforcing its new 13 SEER (up from 10 SEER) energy efficiency standard for all new a/c units sold in the US. The primary...
  41. N

    Efficiency Homework Help: Calculating Carnot Engine Ratio for Heat Engines

    In one cycle, a heat engine absorbs 520J from the high-tempt reservoir and expels 390J to a low-tempt. reservoir. If the efficiency of this engine is 68% of the efficiency of a Carnot engine, what is the ratio of the low tempt. to the high tempt. in the Carnot engine? e=1-(390/520)=.25...
  42. N

    Calculating Home Heat Pump Efficiency & kW-hrs of Heat Delivered

    In a home heat pump, heat is absorbed from the Earth by a fluid circulating in buried pipes and delivered to the home interior. Suppose that the heat pump is 40% as efficient as a Carnot refrigerator. If the ground surrounding the pipes is at 5`C and the interior temperature of the house is kept...
  43. S

    Hybrid Efficiency: Gaining Actual Efficiency Benefits

    What is the actual gain in efficiency in a hybrid?
  44. M

    Determining the Efficiency of a Fuel

    Hi, I'm trying to calculate the efficiency of fuels such as gasoline, diesel, methanol, and ethanol. I have collected several properties such as energy content per gallon (btu) and densities for each fuel. I'm a bit confused as to how i can calulate these fuels' efficiencies...
  45. E

    What is the efficiency of the aircraft engines in this scenario?

    A 3.25 * 103-kg aircraft takes 12.5 min to achieve its cruising altitude of 10.0 km and cruising speed of 850 km/h. If the plane's engines deliver, on the average, 1500 hp of power during this time, what is the efficiency of the aircraft engines? I initially believed the power out would be...
  46. A

    Solving Permutations Problems: Finding Algorithms & Optimizing Efficiency

    I have two problems on permutations which I can´t solve now becuase my knowledge about permutations and the necessary tricks is very poor. 1st: Find an algorithm that for given natural N (N<=1000), K and given permutation of N elements will find the Kth composition of this permutation in time...
  47. V

    Efficiency of the Stirling Cycle: Examining the Debate

    I've calculated the efficiency of the Stirling cycle like \eta=\frac{R(T_H-T_L)\ln\left(V_2/V_1\right)}{RT_H\ln\left(V_2/V_1\right)+C_{mV}(T_H-T_L)} Where V_2>1. It's also derived http://www.pha.jhu.edu/~broholm/l39/node5.html" . But my ("Highschool", or secondary school) teacher says...
  48. L

    Calculate the ideal (Carnot) efficiency of a heat engine

    Calculate the ideal (Carnot) efficiency of a heat engine operating between 23.0 degrees and 515 degrees. How much heat would be rejected by the engine if 1.00 x 10^6 calories were taken from the high temperature resivoir. Would you just use e=1-(T(c)/T(H))? And for the second part i don't...
  49. S

    Calculating Efficiency of a Coal Fired Plant - 700 MW Electrical Power

    A coal fired plant generates 700 MW of electrical power. The plant uses 5.8 * 10^6 kg of coal each day. The heat combustion of cal is 3.3 * 10^7 J/kg. The steam that drives the turbines is at a temperature of 320 C, and the exhaust water is at 45 C. Note: 700 MW= 7.0 * 10^8 J/s = 6.0 * 10^13...
  50. C

    Otto Cycle - Thermodynamics - Efficiency

    Please help with the following question, completely lost: The behavior of a four stroke gasoline engine can be approximated by the so-called Otto cycle. The process is as follows (6 steps): 1) Isobaric Intake (from V=0) at atmospheric pressure up to volume V1 (maximal volume)...
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