Efficiency Definition and 948 Threads

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. F

    Energy, temperatures and efficiency

    Hi all Working through a past paper as I have an exam tomorrow and can't quite see where to start with the following question. Homework Statement A steam engine produces 2.4 kJ of work per cycle for a heat input of 6 kJ. If the temperature of the hot source for the engine is 600 °C and...
  2. D

    Heat Engine Carnot Efficiency question

    Homework Statement A heat engine has a carnot efficiency of 0.11. How much internal energy does this engine use in order to do 5.1 x 10^4 joules of work? How much heat does this engine give off/exhaust?Homework Equations (change in)U=Q-W W=(change in)E
  3. S

    Determine the percent efficiency

    1. Determine the percent efficiency of the system www.imageshack.us/photo/my-images/818/photokt.jpg2. Ek=\frac{mv^2}{2} Eg=mgh W=FΔd W=ΔE 3. I am assuming energy is lost in this system due to friction possibly. Also assuming gravity is 9.81m/s^2 The mass of the the suspended object will be...
  4. T

    Calculating Electrical Energy Input for 70% Efficient Lift Motor

    Homework Statement A lift motor is 70% efficient. It dose 450 000j of work lifting a load to the top floor of a building. Homework Equations What electrical energy input is required to do this? The Attempt at a Solution I first did output/input * 100 I transposed the formulae...
  5. B

    What is the engine's thermal efficiency?

    Homework Statement A heat engine using 110g of helium as the working substance follows the cycle shown in the figure. http://session.masteringphysics.com/problemAsset/1074114/5/19.P59.jpg What is the engine's thermal efficiency? Homework Equations n=W/Q_h The Attempt at a...
  6. G

    Maximum efficiency of an engine taking heat from two hot reservoirs

    Homework Statement A heat engine is taking identical amounts of heat from two hot reservoirs at temperatures ##T_{H1}, T_{H2} ## doing work and then heat to a cold reservoir ##T_C ## What is the maximum efficiency of this heat engine? Homework Equations For a Carnot cyle it is ## \eta = 1 -...
  7. K

    Jump Efficiency TheoryI am young so please no mocking.

    "Jump Efficiency Theory". I am young so please no mocking. This is a theory i have created that judges how efficient a jump is with respect to a specific distance. This theory is going to be used mainly for the Long Jump sport. For example let's say you have to jump across a whole with a...
  8. B

    Calculating the efficiency of a water turbine

    Hi, I am having trouble calculating the efficiency of a water turbine. The turbine in question closely represents a cross flow water turbine. I have tested the power rating experimentally using a small DC motor and have found the output to be 400 mW. I now need to find the power...
  9. M

    How Does Efficiency Loss Affect Voltage and Current in a Transformer?

    Homework Statement A step-down transformer going from 240 V to 12 V is 95% efficient. The input current is 20 A. a) Determine the primary turns: secondary turns ratio necessary in order to maintain a 12V output. b) Determine the output current. I have solved it as if I needed an secondary...
  10. P

    ATH 101: Efficiency of Isobaric Expansion for Monatomic and Diatomic Gases

    In a heat engine we ultimately care about the efficiency of the entire cycle. That is, what percentage of the heat which flows into your system is converted to work. However, you could certainly ask that same question for an individual step in a cycle. Specifically, determine the efficiency of an...
  11. C

    Boiler efficiency and fuel consumption

    Homework Statement A boiler is to produce 6250 kg/h of steam superheated by 40 oC at a pressure of 2.1 MN/m2. The temperature of the feedwater is 50 oC. If the thermal efficiency of the boiler is 70%, how much fuel oil will be consumed in one hour? The calorific value of the fuel oil used is...
  12. K

    Carnot engine efficiency * Carnot refrigerator efficiency

    Carnot engine efficiency is: \eta_{work} = 1 - \frac{T_c}{T_h} Carnot refrigeration efficiency is: \eta_{cool} = \frac{ T_c }{T_h-T_c} \eta_{cool} = \frac{ 1 }{\frac{T_h}{T_c} - 1} Simple multiplication should give me the efficiency where both the engine and the refrigeration share the...
  13. fluidistic

    Efficiency of a cycle from a diagram

    Homework Statement Calculate the efficiency of the heat machine that is shown in the figure. Draw the corresponding Carnot cycle diagram in the S-T plane. Homework Equations \varepsilon = \frac{ \Delta W}{\Delta Q}. \Delta Q = T \Delta S The Attempt at a Solution My problem lies in...
  14. N

    Calculating Efficiency of Diesel Cycle

    1. Homework Statement given: diesel cycle, P1V1 P2V2 P3V3 P4V4 - all known T1 = 20°c specific heat capacity constant pressure = 1000j/kgk specific gas constant = 287j/kgk compression index = 1.4 2. Homework Equations heres where i am stuck! 3. The Attempt at a Solution Hi...
  15. N

    Calculating diesel cycle efficiency

    Homework Statement given: diesel cycle, P1V1 P2V2 P3V3 P4V4 - all known T1 = 20°c specific heat capacity constant pressure = 1000j/kgk specific gas constant = 287j/kgk compression index = 1.4 Homework Equations heres where i am stuck! The Attempt at a Solution Hi all, I am...
  16. J

    How Does Efficiency Impact Velocity Ratio in a Third Class Lever?

    Homework Statement Calculate the velocity ratio of the system. Third Class Lever Efficiency = 65% Mechanical Advantage = 1/6 Work Put In 3000J (I know if the system was theoretically 100% efficient the velocity ratio is 1/6 or 0.167) Homework Equations Velocity Ratio =...
  17. U

    Why Can Heat Pumps Have an Efficiency Greater Than 1?

    In my thermodynamics class we're talking about heat pumps (i.e. refrigerators and such). When talking about a typical heat engine (carnot or not) it makes sense to me to talk about the efficiency of the engine η=1-\frac{Q_{l}}{Q_{h}}, because it clearly represents how much bang you get for you...
  18. A

    Carnot Cycle: Exploring Heat Efficiency and Adiabatic Processes

    I have some trouble understanding the carnot cycle and why you have to make it so complicated, i.e. this process involves 2 isothermal and 2 adiabatic processes. If you want an engine with maximum efficiency why can't you just have a system whose temperature is just a tiny inch above your hot...
  19. M

    Medical Can one change their brain's efficiency?

    Can one do anything to sort of rewire the brain, so to speak. For instance, say I continually teach myself new subjects all the time. Not multitasking- just sort of "hey i learned ___, now i can teach myself ___". Can my brain get better at learning? By better I mean more efficiently.
  20. C

    Increasing the efficiency of a simple electric motor?

    Okay, so I have a simple D cell battery, enamel coated copper wire loop and a magnet. I can easily get the copper wire loop to spin if I scratch away part of the enamel (that side which touches the stand) off the ends of the wire, run current through a stand, and position the magnet at just the...
  21. P

    Automotive Fuel Efficiency: Car #1 vs Car #2 | Ask an Expert

    The qwustion is: 2 identical cars with their engine rev 2000rpm. The only difference is that car num #1 is in 4th gear and car num #2 is in 3rd. Which car will use more fuel per minute? Considering they are driving on leveled ground. And does it Make a difference if they are going uphill...
  22. T

    Calculate the Motor Efficiency when?

    An electric motor drives an electric generator.The 2hp motor draws 15A from a 120V D.C source and the generator supplies 5A to a 48Ohm LOAD. It is given that 1hp= 745.7W Calculate the motor efficiency. Calculate the generator efficiency. Calculate overall efficiency. Ok soo I...
  23. M

    Effects of propylene glycol on heat transfer efficiency

    I'm trying to calculate the heat loss of efficiency due to increasing the mixture of propylene glycol in a heat transfer fluid compared to water.. For this I'm saying that water has a heat transfer efficiency of 100% (relative only) Im looking for multiple data points to create an equation...
  24. S

    What Power Values Are Used in Transformer Efficiency Calculations?

    When I calculate efficiency of a transformer, I use output power/imput power x100%. Then what are these power values? Is the power the power in a load or the total power coming out of the transformer (meaning it includes the joule heating)? Then also what about the input power, which values do I...
  25. T

    Efficiency Calculation for Mechanical System with Incomplete Information

    Homework Statement Hey I've attached the question. My main problem is figuring out how to start. Homework Equations not exactly sure, PE=mgh? efficiency= used power/total power *100 = used power/ 2950 * 100... The Attempt at a Solution i calculated the potential energy...
  26. M

    Amplifier efficiency calculations?

    Would the efficiency calculated using the P output/P input x 100 get the same answer as calculating the efficiency using the RMS input and output values? If so why?
  27. C

    Finding efficiency between transformers.

    Ok, I have a primary and secondary coil. I set up a transformer between them. Each has 400 turns of coil(N). The primary coil produces a potential difference of 2.988 V. The secondary coil has a potential difference of 0.0551 V. For the efficiency, I used the equation (Np*Vs)/(Ns*Vp) * 100%...
  28. D

    Full Wave Rectifier Efficiency: Why is it More Efficient?

    Is it true that a full wave rectifier is more efficient than a half wave and if so why?
  29. C

    Bioenergy: how to measure the efficiency of different materials

    Hello all! I chose not to follow the given format, as my question is kind of unique. I hate to be one of those people who just create an account for one thread (as I usually try to avoid this), but my situation is quite urgent. I have a project due Friday, in which I plan to take different...
  30. K

    Calculating Efficiency of an Ottos Cycle: I Need Help!

    I have made an Ottos Cycle graph and found the area Wnet and W12. I now have to find the efficiency η = Wnet/W12 I have found that to be 0,20 but I have no idea what this tells me about the work or anything. I need help.
  31. M

    Carnot Efficiency vs Rankine Efficiency

    Hi, Given value of top and bottom temperatures can anyone explain why the Ideal Carnot Cycle is more efficient than the Rankine cycle but why the Rankine is the preferred model? I know that in the Carnot the pump would have to be able to deal with a mixture of steam and water and the turbine...
  32. D

    Efficiency of domestic induction heater

    What is the heating efficiency of a domestic induction heater as compared to a simple electrical heater and microwave oven? Please give comparison on the basis of Kilowatt hour consumed.
  33. B

    Dim LED with Transistor Switch - Why?

    Hello, I've just been playing around with a 2n3904 transistor and 3V coin battery. I noticed when powering an LED with a transistor switch the LED is significantly dimmer than when powering the LED directly. Why is this? Is it because 0.7 volts is siphoned off just to turn the transistor on?
  34. JJBladester

    Energy efficiency - purchasing the right furnace

    Homework Statement Consider a homeowner who is replacing his 25-year-old natural gas furnace that has an efficiency of 55 percent. The homeowner is considering a conventional furnace that has an efficiency of 82 percent and costs $1600 and a high-efficiency furnace that has an efficiency of...
  35. S

    What is the efficiency of a pulley and how do we calculate it?

    Homework Statement I'm on my last question for my coursework and this is it. I have managed to find out how to calculate the efficiency of a pulley but not "what is the efficiency of a pulley" Could someone please help me. Homework Equations Efficiency = (Mechanical Advantage /...
  36. G

    Pulley Efficiency Problem (How much rope must be pulled)?

    Homework Statement A pulley system has an efficiency of 71.5 percent. How much of the rope must be pulled in if a force of 641 N is needed to lift a 160 kg desk 2.51 meters? Homework Equations IMA = De/Dr MA = Fr/Fe Efficiency (%) = Wo/Wi Efficiency (%) = MA/IMA I have absolutely...
  37. mheslep

    Propeller efficiency and energy loss

    Googling for information on the topic leads me to graphs such as this, which suggest that if Beta and advance are optimal efficiency tops out at 85% or so. Some questions: 1) Is the ~15% lost energy converted to heat, or is there some stray kinetic energy in airflow that is somehow unusable as...
  38. C

    Exploring Equity & Efficiency: Chapter 1 of Textbook

    Hey! This is not a homework question, I'm merely studying this textbook out of pleasure! I'm trying to understand some bits of the theory in chapter 1 of this book. What is equity exactly? From the definition given in page 5: equity the property of distributing economic prosperity fairly...
  39. S

    Efficiency of a hollow sphere of bouncy balls?

    I'm tasked with creating an egg protector that bounces. I'm thinking of gluing bouncy balls together side-by-side around a template sphere. The glue being used should be very strong, it's a super glue that works on rubber. Would this be able to bounce effectively? Will I need to add mass...
  40. S

    How Much Mass Must Be Pumped from the Ocean Floor to Generate 50kW of Power?

    Homework Statement The original is in German, but I will try my best to translate. A power generator uses the temperature difference between surface ocean temperature and sea bottom temperature (27C and 6C) to generate electricity. The power outage is 50kW at 10% of the Carnot efficiency...
  41. M

    Concept of a new thermopiple array above 10% efficiency?

    Is is possible to design a more efficient thermopipe using a laminer flow heat source? A. Test piece incorporates a length of 1.5 x 24 " black iron pipe to produce laminer flow. B. A variable fan is used to input the air into one end of the pipe. C. Fuel source is a 20 lb. propane bottle...
  42. S

    Is a Zero Efficiency Machine Possible and Thermodynamically Stable?

    Lets say if we have an induction motor or any motor whose rotating shaft acts as a source of alternating emf to another motor and rotating shaft of this motor again acts as a source of alternating emf to third motor and so on... We connect such a finite number of motors and we call it as a...
  43. A

    Higher efficiency - 2 stroke or 4 stroke diesel engine?

    Hi evry1! Just wanted to know that which has got higher efficiency - 2 stroke diesel engine or 4 stroke diesel engine. I believe that direct injection of fuel in diesel engines prevents the loss of unburnt fuel in exhust of 2S engine. And simpler mechanism and lesser no. of moving parts in 2S...
  44. G

    What is the efficiency of this reversible engine?

    Homework Statement A reversible engine contains 0.5 mol of an ideal monatomic gas and operates using a cycle, similar to that shown in Fig. 19.21 on page 324 of the textbook, consisting of constant volume and constant pressure segments. (You will need to draw your own diagram using the data...
  45. N

    Impulse, momentum and efficiency to find height formula

    http://a6.sphotos.ak.fbcdn.net/hphotos-ak-ash4/388044_10150449591037412_816037411_8386849_1415117382_n.jpg Homework Statement A ramp system is set up. Due to friction the ramp has an efficiency of 82%. Two cars of equal mass are allowed to collide and car 1 starts from rest at height h1...
  46. Q

    (21-23) thermodynamics problem. Finding efficiency for the human body

    Homework Statement While running up stairs at a (vertical) rate of 0.30 m/s, a man of 70 kg generates waste heat at a rate of 1300 J/s. What efficiency for the human body can you deduce from this? Homework Equations efficiency of heat...
  47. D

    AZING CLIMBER! What is the efficiency of this mountain climber as a heat engine?

    Homework Statement A 52-kg mountain climber, starting from rest, climbs a vertical distance of 730 m. At the top, she is again at rest. In the process, her body generates 4.1 × 10^10 J of energy via metabolic processes. In fact, her body acts like a heat engine, the efficiency of which is...
  48. E

    Bandwidth efficiency in m - ary psk

    In M-ary psk Rb=Rs*log M log with base 2 Rb- bit rate Rs - symbol rate then bandwidth required for passband signal is B=Rs and bandwidth effeciency = Rb/B=log M log with base 2. Is the above formula for bandwidth efficiency...
  49. S

    PV Diagram Problem (ideal efficiency vs actual efficiency)

    Homework Statement The PV diagram below (I will describe it) shows a cycle for 4.87moels of an ideal gas. The path ab is along an isothermal line. Pressure is in atm and volume in m3 Point a: (.08, 6) Point b: (.24,2) Point c: (.08, 2) Find the ideal and the actual efficiency of...
  50. R

    Law of conservation, and efficiency problem?

    Homework Statement A 2.0x10^2 g pendulum bob is raised 22cm above its rest position.The bob is released, and it reaches its maximum speed as it passes the rest position. Calculate its maximum speed at that point by applying the law of conservation of energy and assuming that the efficiency...
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