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. C

    Thermal efficiency in a reversible cycle for an ideal gas pV diagram

    Homework Statement A heat engine takes 4.0 moles of an ideal gas through the reversible cycle abca, on the pV diagram, as shown. The path bc is an isothermal process. The temperature at c is 600 K and the volumes at a and c are 0.04 m^3 and 0.10m^3, respectively. The molar heat capacity at...
  2. J

    What is the efficiency of the engine?

    if a 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?
  3. A

    Planet gear efficiency. Need help

    I'm having a bit of difficulty figuring out the theoretical efficiency of a compound epicyclic gear train. The math involved is a bit over my head. This train is meant to run at very slow speed under light load. I want to find the theoretical efficiency of the design so I can determine if it is...
  4. M

    How do you test the efficiency of a wobbler steam engine

    I have a project for my sophomore design class to test the efficiency of a wobbler steam engine. I have heard people talk of using a dc motor and connecting it with a belt to the flywheel to see what voltage it produces but I don't know how to do that. In addtion, some have suggested to just...
  5. B

    How Do You Calculate Volumetric Efficiency in a Twin Cylinder Air Compressor?

    Homework Statement It is required to design a single acting twin cylinder air compressor to deliver 17.2kg/min of compressed air at 7.2 bar. The intake pressure and temperature are 1 bar and 15oC respectively. Compressor speed is to be 300 rpm. Take clearance volume as 5% of the swept...
  6. A

    Gain in Thermal Efficiency from Additional Expander Unit

    If a Wankel gasoline engine was to be fitted with a compact and efficient positive displacement additional expander unit such that the normal exhaust from the engine was further expanded down to atmospheric pressure before being released to atmosphere, what gain in thermal efficiency could be...
  7. B

    Best efficiency to convert Kinetic into Electric

    I am seeking help with the theory of energy conversion from kinetic energy to electric energy. Is it possible to convert kinetic energy to electric energy at an efficiency higher than 75% If so, how? Specifically, I mean not using heat (cogeneration power plants) or potential energy...
  8. M

    Conservation of energy/ efficiency question.

    Homework Statement A climber's gravitational potential energy increases from 14000 J to 21 000 J while climbing a cliff. She expends 18 000 J of energy during this activity. What is the efficiency of this process? Homework Equations Efficiency= useful output/ total input Total...
  9. A

    Thermodynamics: Carnot efficiency

    Homework Statement In one location, the average daily temperature varies sinusoidally between 35C in summer and 0C in winter. The ground temperature below 2 m underground is the annual average temperature. A heat pump / air conditioner unit must deliver air to a house at 30C in winter and...
  10. N

    Why are electric space heaters only 100% efficient?

    It appears everyday electric space heaters, that is resistance heaters, are virtually 100% efficient. No matter what resistance material is used, there is only 3.413 BTU per watt hour of heat output; in other words, all 1500 watt heaters consume the same amount of electricity and produce the...
  11. J

    Polytropic efficiency vs isentropic efficiency?

    been reading in many books that polytropic efficiency is always recommended over isentropic efficiency. what are the advantages of using polytropic efficiency? what makes it different from isentropic efficiency? it is also told that polytropic efficiency is independent of pressure...
  12. I

    Something > Carnot efficiency ? WTF?

    Something > Carnot efficiency ? WTF? So I've made a very simple, ideal model of a heat engine, and my calculations just don't match up to the carnot thing: efficiency = 1-(Tc/Th) It looks like this: I supposed a rectangular block, base of 1cm by 1cm, and a piston free to move up and down...
  13. P

    How much energy to heat a room, and heat pump efficiency?

    O.K. this is maybe a large question... I am trying to find out how much energy it would take to do the work of a heat pump compressor that would be required to heat a... let's say 10 ft. x 10 ft. room of a typical house. I know there are a lot of variable here... What I am trying to...
  14. J

    Maximum efficiency of a heat engine

    Homework Statement Calculate the maximum possible efficiency of a heat engine that uses surface lake water at 19°C as a source of heat and rejects waste heat to the water 0.100 km below the surface where the temperature is 4.1°C. Homework Equations eta = 1 - Tc / Th The Attempt at...
  15. G

    Calculate efficiency for an incandescent light bulb?

    How does one calculate efficiency for an incandescent light bulb? Assume the bulb is 40 W, has a tungsten filament at temp. ~ 2800 K. The bulb would be used for heating in a device. If we assume blackbody: From Wien's displacement law, the maximum wavelength is 9.99E-7 m. Fromt the...
  16. G

    Efficiency and temperature of cooking device

    Homework Statement Suppose a cooking device has a power of P Watts. The temperature of the bulb which radiates heat is determined to be T (in Kelvin). Write an expression for efficiency in terms of T and P. Homework Equations E = \sigmaT^{4} Stefann Boltzmann equation \eta=...
  17. W

    Calculating Work Output from Thermal Efficiency of Car Engine

    Homework Statement The power output of a car engine running at 1900 is 600 kilowatts per hour. How much work is done per cycle if the engine's thermal efficiency is 30.0 percent Homework Equations thermal efficiency=w(out)/Q(hot) The Attempt at a Solution It wants the answer in...
  18. A

    How Does Diesel Engine Efficiency Compare to Gasoline Engines?

    Homework Statement The figure shows the thermodynamic cycle of a diesel engine. This cycle differs from that of a gasoline engine in that combustion takes place isobarically. The compression ratio r is the ratio of maximum to minimum volume: r = V_1 /V_2. In addition, the so-called cutoff...
  19. M

    Why water turbine have higher efficiency then steam turbine?

    I wonder why water turbine (like in hydroelectric power plant) has, in most design, more then 90% efficiency when steam turbine around 30%. In both cases we converting the pressure to work, so why such a difference in efficiency?
  20. L

    Carnot engine efficiency and exhaust problem

    Homework Statement The exhaust temperature of a Carnot heat engine is 121◦C. What is the intake temperature if the efficiency of the engine is 13.4 %? Answer in units of ◦C. Homework Equations e=1-(Tc/Th) The Attempt at a Solution This seems like just a plug and chug problem...
  21. F

    Find the efficiency of the heating

    Homework Statement A 2.5kW electric kettle takes 3 mins to raise the temperature of 1.2kg of water from a temperature of 20 degrees C to a temperature of 100 degress. The specific heat capacity of water is 4.2kJ/(kg K) Homework Equations So far I know that we're either using P=vit ot...
  22. C

    Optimizing Beam Size for Increased Diffraction Efficiency

    In order to increase the diffraction efficiency of the AOM, we need to reduce the beam size of the laser. According to the manual of my AOM, it needs to have the beam size of 220um to get more than 90% diffraction efficiency. So, I decided to do so by putting a lens in front of it and...
  23. T

    How much is the energy efficiency of the process of photosynthesis?

    Homework Statement During photosynthesis found that a plant is necessary to absorb 8 photons of red light with wavelength 6850 Å to produce an O2 molecule. The average energy storage during photosynthesis is 112 kcal per mole O2. Calculate the energy efficiency of the process of...
  24. U

    How much energy does it take to climb stairs?

    1. Efficiency is defined as work-out/work-in. Muscles operate with an efficiency of about 20% in converting energy internally into work externally. Accordingly, how much energy will be expended by a 60 kg person in the process of ascending several flights of stairs to a height of 25 m...
  25. A

    Efficiency of Indian kino oil as a biodiesel

    I am planning to test the efficiency of Indian kino oil as a biodiesel... How do I do it? I only have access to my school chemistry lab...
  26. U

    Efficiency of Motor: 6V, 0.25A, 200g Weight, 4J Potential Energy

    A student performs an experiment in which an electric motor is used to lift a 200g weight through 2m, thus increasing its potential energy 4J. from measurements of the rate at which the weight is lifted the efficiency of the motor is to be determined. Two different voltages were used and the...
  27. N

    Electrolyte + electrolysis efficiency

    Hello, Does adding electrolyte increase the efficiency of h2o electrolysis? If so, is there a formula to figure out ideal electrolytes, etc? Does the electrolyte weaken the H2O covalent bonds, or just allow current to flow easier between electrodes? Thanks,
  28. A

    Efficiency of heat pump and refrigerator

    I know the formulas for efficiencies e of heat pump (it is e<=Tmax/(Tmax-Tmin)) and refrigerator (e<=Tmin/(Tmax-Tmin)), where Tmax and Tmin are temperatures of warmer and colder (respectively) involved containers. These formulas make me puzzled, as efficiencies seem to be possibly bigger than 1...
  29. H

    Experiment about efficiency of bisulphite as wine preservative

    Homework Statement Could you suggest an experiment to determine the efficiency of sodium hydrogensulphate(IV) as a wine preservative? 2. The attempt at a solution I just think that since wine contains ethanol, which would be oxidized in air to form ethanoic acid slowly, by comparing the pH...
  30. S

    Single Dish Radio Astronomy Inefficiencies

    Hi, What is the cause of inefficiencies in single dish radio astronomy? I think it's related to the efficiency of the dish itself ...that the effective area of the dish is less than its total area. Is that right? If so, why is that the case? Thanks, San
  31. Y

    Finding Efficiency from a P-V Graph

    uh...just wondering but how do you find out the efficiency from a P-V graph?
  32. J

    Efficiency of an imaginary ideal-gas engine cycle

    Homework Statement The figure represents a simplified PV diagram of the Joule ideal-gas cycle. All processes are quasi-static, and C_P is constant. Prove that the thermal efficiency of an engine performing this cycle is \eta = 1 - \gamma \frac{\frac{V_{1}}{V_{2}} - 1}{\frac{P_{3}}{P_{2}}...
  33. J

    Efficiency of an engine performing the Joule ideal-gas cycle.

    Homework Statement The figure represents a simplified PV diagram of the Joule ideal-gas cycle. All processes are quasi-static, and C_P is constant. Prove that the thermal efficiency of an engine performing this cycle is 1 - \left(\frac{P_1}{P_2}\right)^\frac{\gamma - 1}{\gamma}...
  34. P

    Thermodynamics - efficiency from pv diagram

    Homework Statement Determine the efficiency for the cycle shown in the figure, using the definition. Assume that the gas in the cycle is ideal monatomic gas. Compare with the efficiency of a Carnot engine operating between the same temperature extremes. see attachment Homework...
  35. P

    Thermodynamics - engine efficiency

    Homework Statement A reversible engine contains 0.20 mol of ideal monatomic gas, initially at 600 K and confined to 2.0 L. The gas undergoes the following cycle: Isothermal expansion to 4.0 L. Isovolumic cooling to 300 K. Isothermal compression to 2.0 L. Isovolumic heating to 600 K...
  36. e2m2a

    Efficiency of linear alternator

    Interesed in practical maximum efficiency of linear alternators. Suppose an object with a permanent magnetic attached moves along a linear track with a constant velocity, such that its kinetic energy is 1 joule. The object "collides" with a linear alternator or generator, such that the magnet...
  37. e2m2a

    Electro-magnetic pulser efficiency

    Suppose there is an object with a permanent magnet attached to it that can slide on a linear track. The object is initially at rest and the permanent magnet alligns with the axis of an electro-magnet. If the electro-magnet is pulsed on momentarily with a current so that the object acquires a...
  38. Phrak

    Tesla Motors claims 114% efficiency

    Tesla Motors claims a "well-to-wheel" efficiency of 1.14 http://www.teslamotors.com/efficiency/well_to_wheel.php" What in the blue blazes are they talking about?
  39. M

    Efficiency of nuclear powerplants

    guys. help me to explain this question.. The efficiency of nuclear powerplants used to produce electricity is about 40%. Under what condition this conversation efficiency could be increased to 100%? What difficulty might be encountered?thank you guys!
  40. A

    Energy efficiency and home insulation

    I live in a very hot climate. I have upgraded my windows to double pane thermal with some some success in cooling my home. I have been considering both additional fiberglass insulation and a radiant heat barrier for my attic as the air conditioning bill is still horrific and rates keep rising...
  41. S

    What is the Efficiency of an Ideal Gas Engine?

    Homework Statement An ideal gas engine that works according to the following cycle. Find the efficiency of this engine assuming that the heat capacities of the gas may be taken to be constant. Recall that the efficiency may be defined as: \eta = \frac{Net work done over full cycle}{Heat...
  42. Z

    Solar cell Efficiency & thermal ?

    Is 55°C best status for solar cells?
  43. rootX

    Balancing Time and Efficiency: My Struggle

    Does anyone else struggle with the loss of time? Each day I end up wasting at least 4-5 hours to unproductive causes[activities for which I did not allot my time]. Like today at 6 PM, I decided not to watch movie and do some work. But, for some unknown crazy reasons, I end up wasting 4 hours...
  44. O

    Area efficiency of Miles Per Gallon

    My physics professor posed that question to us a while back, and he never gave us the answer. I tried solving it but I had no idea what units to convert it too. Does anyone have any ideas as to what the answer may possibly be?
  45. S

    Physics: Efficiency of toy car going upwards on a slope

    the toy car gains energy by pushin down the "head" of the "driver" and is powered by a spring that powers the wheels. at different heights, it has different spring constant. I mean the slope's angles are changed at different periods of the experiment. I am unable to work out the spring constant...
  46. P

    Why Can't We Significantly Boost ICE Auto Efficiency?

    Why can't we improve the efficiency (miles/gallon) of ICE autos? It seems to me there are two areas that can be used to add efficiency: 1) Heat recovery with some form of a "bottoming cycle" to generate additional torque or electricity from heat lost in the radiator, and 2) Breaking...
  47. P

    Calculate Efficiency of 10.0 kW Motor for 8.5 kg Elevator

    Homework Statement An 8.5 kg elevator is pulled at a constant velocity of 1.0 m/s by a 10.0 kW motor. Calculate the efficiency of the motor. Homework Equations W = change in E = Fd e = Work out/Work in * 100 = energy out/energy in *100 Epotential = mgh Ekinetic = 1/2mv^2...
  48. B

    Solving the Tesla Turbine Bearing Temperature Problem

    I see a lot of references to the 'efficiency' of the Tesla turbine, however, I can't find any actual data. Does anyone have a handle on actual achievable efficiencies of the tesla turbine?
  49. G

    Can Tracking Degree Days Help Improve Energy Efficiency for HVAC Systems?

    As I fine tune our VAV HVAC system (506,000 sq.ft. facility), we'd like to determine the effectiveness of our adjustments over time. As we both heat and cool portions of the building at the same time (electric VAV reheat), we need to apply degree days to the analysis. How is that done...
  50. T

    Digestion-carbohydrate-ATP-energy efficiency

    how efficiently do we turn our food into energy? I have been kind of wondering if in the future it might be possible, and, a good idea to use biological processes to make energy out of food for energy? I know we can already process plants and extract sugar to make ethinol, or oil for...
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