What is Efficiency: Definition and 945 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. C

    PV power plant efficiency math problem?

    Homework Statement The controversial Cheviot open-pit coal mine in Alberta, Canada occupies 7,455 hectares (one hectare= 10^4 m^2) and produces 1.4 million tonnes of coal per year. a) use the energy content of coal of 29 MJ/kg to find the power in watts corresponding to this rate of...
  2. C

    Power used to heat water and efficiency math problem

    Homework Statement A household uses 100 gallons of hot water per day (1 gallon of water has a mass of 3.78 kg) and the water temperature must be raised from 10°C to 50°C a) find the average power needed to heat the water. b)Then assume you have solar collectors with 55% average...
  3. P

    Energy conversion efficiency of each bounce

    1. i drop a ball (mass 20 grammes) from a height of 10 meters, after 3 bounces it rises to a height of 2 meters, what is the energy conversion efficiency of each bounce? 2. I've been stuck on this for the last hour and have nothing any help would be great. 3.the closest i got was...
  4. R

    Seawater power plant efficiency

    1. Problem statement A power plant generates electricity from the difference in sea temperature. At the surface of the sea the temperature is 27°C. At the bottom of the sea the temperature is 6°C. a) What is the highest efficiency that this plant can have? b) If the power plant generates...
  5. S

    Mylar to increase efficiency of solar battery charger?

    I just got my hands on a solar battery charger with a set of usage specifications that makes me believe it will only be useful some four days a month and will take more or less such time to charge a single set of batteries, despite promises on the contrary in the instructions. Since the case is...
  6. F

    Hydraulic motor efficiency conundrum

    Hello, I'm trying to compare efficiency of different hydraulic motors by looking at unit of output per unit of input, viz: \frac{rpm × torque}{pressure × flow} I'm a bit flummoxed by one set of motor specs, for Eaton Duraforce motors, which is attached below. these motors seem to...
  7. D

    How Is Engine Efficiency Calculated Using V1/V2 in Thermodynamic Cycles?

    Homework Statement Four thermodynamic processes A,B,C,D are shown in the picture. A and C are adiabatic processes. Pressure is held constant during B, and volume is constant during D. An engine run from A->B->C->D->... What is the efficiency of this engine (in terms of V1/V2)? Homework...
  8. naima

    Bell's inequality when efficiency < 1

    Hi PF Somebody gave me this link could you help me to understand why (9) has to be inserted in (7) when the efficiency \eta < 1?
  9. H

    Proving that a heat engine cannot exceed the carnot efficiency

    In many textbooks, a proof is provided where the work output of a super-efficient heat engine is provided to a carnot refrigerator, with the net result that a spontaneous heat transfer occurs from the cold reservoir to a hot reservoir. Let's use some numbers, TH = 600 K and TL = 300 K, so...
  10. M

    Electric motor load vs efficiency historical background

    Is there a physicist who has discovered this, and could you explain how he/she did it? I was trying to find it on the internet, but it only gives me a lab review of load vs efficiency. thank you
  11. siddharth23

    Higher efficiency in spray painting metal tanks.

    When a hand spray painting gun is used to paint say metal tanks, about 80% of the paint is lost in the air. This not only leads to a wastage of paint, but also the paint partivles settle on other stuff causing paint spots. What method can be used to reduce this? One is ionizing the tank...
  12. M

    Pelton wheel's theoretical speed for max efficiency

    Homework Statement A Pelton wheel is driven by five identical jets. The runner has a diameter of 3,8 m, fixed in a horizontal position. The head from reservoir level to nozzles is 350 m and the efficiency of power transmission through the pipeline and nozzles is 90%. The relative velocity...
  13. A

    Electromagnet heat source and efficiency

    So.. I'm a biomedical engineer, and a new technology that is arising is being able to control magnets that "swim" around the body using electromagnets oriented around the outside of the patients body. It has been said that electromagnets can't be used on the inside of the patient because they...
  14. M

    Efficiency of a Light Bulb: Calculating Energy Transfer

    Homework Statement "A light bulb is 85% efficient. If it is supplied with 60J of electrical energy, how much of this energy is transferred to its surroundings as light energy? The attempt at a solution So I calculated that 85% of 60 is 51J, however I don't know if being "efficient"...
  15. C

    Efficiency of air powered water pump

    Hi, I'm thinking of a water pump with only the valves as moving parts - the compressed air simply displaces water from a cylinder. I understand it's a solution for where it's easier to deliver compressed air than electricity to the pump site. My question is: where are the energy losses in...
  16. F

    Maximizing Generator Efficiency for Common Lighting and Power Loads

    Dear All, How can I improve the efficiency of a generator which is connected to common lighting and power loads? If there any use of capacitor bank in the Main Panel side if there only using the generator supply
  17. S

    CSP power plant efficiency calculations

    Hello, please I want to know how to calculate the overall efficiency of a concentrated solar power plant (CSP) which uses parabolic trough concentrator,so please if you can provide me with detailed information and calculation method. Thank you
  18. S

    2 Questions - Heating room air, and fuel combustion efficiency

    2 Questions -- Heating room air, and fuel combustion efficiency Homework Statement 2 questions. In advance, i needed to translate it so i am sorry if it is states incorrect. I really did my best to do it right. 1. The density of air at 1 atm and 10.0 ° C is equal to 1.24 kg / m3. (cubic...
  19. B

    Measuring efficiency of bioluminescent bacteria

    Hi, I want to run an experiment to try and experimentally determine the efficiency (as in what percent of energy is converted to light) of bioluminescent bacteria (V. Fischeri), and compare it to the efficiency of a "traditional" light source, like an LED or an incandescent. I know how I...
  20. R

    How Do I Calculate Thermal Efficiency with the Brake Equation?

    Can you please help me? I am trying to calculate this equation but can't get correct answer: Thermal Efficiency, Brake = 1/(bSPC x QHV) bSPC (brake Specific fuel consumption) = 0.396 kg/KWh QHV (Heating Value for fuel) = 44 MJ/Kg The correct answer is meant to be: Thermal Efficiency, Brake...
  21. W

    How to calculate a PMA's efficiency

    Hello, I want to start by stating I am a bookkeeper and do not have much experience or depth of knowledge in electronics...so get you chuckles now. What I would like to do is augment my electric supply with a Windtronics type generator. I am opting for this style as I am not able to put a 30...
  22. Saitama

    What is the Efficiency of a Cyclic Process?

    Homework Statement (see attachment, ignore the arrows made with the pen) Homework Equations The Attempt at a Solution Efficiency of a cycle is defined as ##\eta=\frac{W}{Q}## where W is work done and Q is heat input. W can be easily calculated by finding the area enclosed...
  23. 1

    Please help - Efficiency of car engine question Unit test tomorrow

    Please help -- Efficiency of car engine question... Unit test tomorrow Homework Statement A car's engine is only 12% efficient at converting chemical energy in gasoline into mechanical energy. If it takes 18000 N of force to keep the car moving at a constant speed of 21 m/s, how much chemical...
  24. 1

    Kinetic energy efficiency question

    Homework Statement A roller coaster descends 55m from the top of the first high point to the first low point in the track. The roller coaster converts gravitational potential energy to kinetic energy with an efficiency of 50.0%. What is the velocity of the roller coaster at the bottom of the...
  25. D

    Strain potential energy and efficiency question

    Homework Statement A sphere of mass 0.1 kg is pushed against a rubber band catapult with a force of 80N, and released upwards. Calculate: A) The strain potential energy when stretched by 0.3m B) The work done by the applied force C) The speed of the sphere when released D) The...
  26. A

    Published paper proving that Carnot efficiency can be exceeded

    I've theoretically proved that heat to work can be converted at 100% efficiency by proposing a system, named as the Blue system. And I've also proved that the entropy of the universe increases even if this system operates at 100% efficiency. The implication of this being that the Carnot theorem...
  27. H

    Calculating Efficiency: Find Useful Energy Output

    I have built a plumbing test rig for my project. I have a couple of electrical devices on this rig and need to find out the efficiency of them/the rig. I have looked online to find equations and have found all the relevant material except for the useful output energy. in all the examples they...
  28. X

    O efficiency of Diesel cycle

    Homework Statement Derive a formula for the efficiency of the Diesel cycle, in terms of the compression ratio V1/V2 Homework Equations e=\frac{W}{Q_{h}} w= ∫pdV The Attempt at a Solution Now I know I should have used e=1-\frac{Q_{c}}{Q_{h}} to get it but he said it is...
  29. Q

    Does the load on a transformer affect its efficiency?

    Homework Statement A transformer has 400 primary coils and 200 secondary coils. The primary voltage is 200 V, and the current is 2 A. A lamp is connected to the secondary coil. The efficiency of this transformer is 50%. Find the resistance of the lamp. Homework Equations V=IR η=P in / P out...
  30. G

    Does the Efficiency of a Steam Boiler Generator Depend on Load?

    Hi, my friend and I were having discussion on the efficiency of a steam boiler in our thermodynamics lab (he has a model of a steam boiler in the thermodynamics lab). He told me that the efficiency of the steam boiler generator is dependent on the load. I thought it was absurd, saying that the...
  31. F

    Work energy efficiency car problem

    Homework Statement Gasoline has an energy content of about 132.65 MJ/US Gallon. An average passenger car has a mass of 1500kg. The average vehicle experiences a drag force F(drag) = (0.176 kg/m)v^2, regardless of road conditions. A uniform and level road surface provides a 'rolling...
  32. J

    Efficiency of engine taking diatomic ideal gas through cycles

    Homework Statement What is the thermal efficiency of an engine that operates by taking n moles of diatomic ideal gas through the cycle 1 -------> 2 -------> 3 -------> 4 ------> 1 shown in the figure ? http://s3.amazonaws.com/answer-board-image/2d50cb1e-1bc6-4325-acf6-fe1df4f0a7b5.jpeg...
  33. C

    How Efficient Are Human Leg Muscles?

    Please refer to the image attached. For Q5, I did it like this: Output energy = (50kg x 10 x 0.35metre) x 30times x 4minutes And divide the answer by 120kJ. The percentage I got is 17.5 Joules but the answer is 15J. Did I do anything wrong? For Q6, the temperature should fall, correct...
  34. S

    How does the pressure ratio affect the efficiency of a gas turbine?

    Hello, In http://www.aerostudents.com/files/gasTurbines/gasTurbinesFullVersion.pdf it is shown that the efficiency of a gas turbine is determined by the Brayton cycle and it depends on the pressure ratio ε. ε is the compression ratio before fossil fuel burning invests further energy into...
  35. M

    Help with Efficiency of a motor

    This is from so long ago, I do not even know what the experiment was about any more if anyone can tell me what lesson's name or can explain to me how I can start https://fbcdn-sphotos-g-a.akamaihd.net/hphotos-ak-ash3/66969_525098604196152_1821545085_n.jpg
  36. W

    Comparing Carnot efficiency to Stirling efficiency

    Homework Statement In the problem, we were to derive work and heat for each leg of the cycle. Then we are asked: In the definition of the efficiency of this cycle, η =W Qpos , where Qpos is the total positive heat flow to the engine, what is the efficiency of the cycle when Th = 700K and Tc =...
  37. T

    Adiabatic steam turbine - find the second law efficiency

    Homework Statement The Attempt at a Solution So pretty much for this question you want to find the actual work output of the turbine and the reversible work output. To find the reversible (theoretical) work output, you know that s2 = s1, so based on that information you can find what...
  38. A

    Thermodynamic Efficiency and the maximum possible electric output

    [b]1. A 2.5GWth nuclear power plant operates at a high temperature of 570°K. In the winter the average low temperature at which it dumps waste heat is 268°K; in the summer it’s 295°K. Determine the thermodynamic efficiency of the plant in each season, and then derive from it the maximum possible...
  39. J

    Finding Mechanical Energy without knowing Efficiency

    Homework Statement A 65 kg man goes for a 72 minute hike up a mountain that is 400.0 metres in vertical height. The energy consumption rate for this climb is 10.1 kcal/min. What is the Mechanical Energy (useful work energy) expended for this hike? (in kcal) Homework Equations ME=...
  40. S

    Confirmation of transformer efficiency

    Homework Statement The problem at hand involved determining the equivalent circuit model of the transformer and then determining its efficiency. I for the life of me cannot get the results that he has provided us with, so perhaps someone here can either confirm my results or indeed confirm his...
  41. R

    Efficiency of power inverters in electric/hybrid vehicles

    I am interested in increasing the range of electric/hybrid vehicles. Increasing the energy density of batteries is something chemists, materials scientists, and chemical engineers worry about. What about from the electrical side though? Can electrical engineers do much to significantly...
  42. M

    How to measure the external quantum efficiency of OLEDs?

    Hello PF, I am currently studying OLEDs (organic light emitting diodes) and have been reading many articles pertaining to the external quantum efficiency of these devices and the various extraction techniques used. In all of these articles, they state the increase of efficiency but do not...
  43. V

    Efficiency of Carnot engine

    The problem: An engine puts an ideal monatomic gas through a clockwise rectangular cycle on a PV diagram with horizontal and vertical sides. The lower left point has a pressure of 1 atm and a volume of 1m^3 and the upper right point has pressure and volume three times greater. Calculate the...
  44. Gh778

    Efficiency to move a curve shape

    Fig 1 : the blue volume has a lot of very small spherical balls in it. Balls are under pressure from external system (weight or other), the potential energy is always the same because the blue volume is constant. When I move the blue volume from position 1 to position 2, I can understand that...
  45. K

    Determining efficiency of multiplication algorithm

    Hi I'm writing a BigNum library for Javascript and have come up with a multiplication algorithm which I think is pretty efficient (a modification of shift/add), but I don't understand O(log ...) notation, so don't really know how to compare my method with something like the Schönhage–Strassen...
  46. I

    Calculate Efficiency with MPG and other things

    My engine has a data plate stating it uses x amount of fuel to make x amount of power at x RPM. I can use that to derive the efficiency but then all other calculations I use, such as finding the HP at a given load using the fuel amount I get with MPG at a given speed, are all derived from that...
  47. Low-Q

    Efficiency of electrical heat vs. mechanical heating

    I have a question about efficiency of electrical heating vs. mechanical heating. Let me explain an example: I have two containers with 1 litre of water each. In one container I use a electric heater (electrical resistance) 1W. In the other container I use an electric motor attached to a...
  48. B

    Determining efficiency of fuel cells

    Hi I need to compare solid working with \frac{1}{2}O_{2}+H_{2}O+2e^{-} \rightarrow 2OH^{-} and H_{2}+2OH^{-} \rightarrow 2H_{2}O+2e^{-} and liquid fuel cells working with H_{2}\rightarrow 2H^{+}+2e^{-} and \frac{1}{2}O_{2}+2H^{+}+2e^{-} \rightarrow H_{2}O My...
  49. K

    Efficiency Of Thin Film Solar Cells

    How does the efficiency of a Thin Film solar cell compare to the efficiency of a single crystal solar cell with reference to the 5 main solar cell parameters ( Iopt , Rs, Rsh, Is and n )? I know series resistance( Rs ) will probably increase in thin film cells because of grain boundaries...
  50. mrspeedybob

    The maximum theoretical efficiency of a heat engine

    http://en.wikipedia.org/wiki/Heat_engine This is one of those threads where the OP proposed a device which will not work and hopefully by the end understands why. So here's the device... Air enters through a long intake tube. At the end of the tube it enters a combustion chamber where fuel is...
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