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

    How Much Oil Can a 65% Efficient 5kW Motor Pump Per Minute?

    Homework Statement I am using a 5 kilowatt motor to pump oil to a holding tank which is 20 m above the pump. If the motor is 65% efficient, how many liters of oil can i pump per minute if 1 liter of oil has a mass of 1.30 kg?Homework Equations ?The Attempt at a Solution ?
  2. F

    Maximum power transfer vs Max power efficiency

    Hello forum, what is the main difference between max power transfer and max power efficiency? In the case of max power transfer, the goal is to transfer the most energy to the load per unit time (impedance matching). Power is I*V and is about delivering energy very fast... High power...
  3. A

    Thermodynamics: Efficiency for Stirling engine

    Homework Statement I'm trying to find an expression for the efficiency of a stirling engine operating with an ideal diatomic gas, and cycling through a volume V and a multiple of its compression ratio, r, Vr. Homework Equations processes: 1-2 isothermal expansion 2-3 isochoric...
  4. N

    Transformer Voltage Regulation and efficiency determination?

    A transformer is rated at 2300/230 V, 15 kVA and 50 Hz. Assume that the transformer is operating at 80% p.f., leading and at rated output the secondary terminal voltage is 230 V. The following parameters for the transformer are given: N1 = 1500 turns N2 = 150 turns r1 = 2.7 ohms r2 = 0.024...
  5. G

    Calculating Power plant's electric output in relation to carnot efficiency

    We were assigned a problem in class, but because it was on guest lecturer material, I am unclear of which given numbers and what equations to use. I do know I am supposed to use: η=TH-Tc/TH But I am confused as to why I have been given 4 variables ...Please Help! Here is the question [1] You...
  6. J

    Thermodynamics: isentropic efficiency and ideal gas model

    Air at 1175 K, 8 bar enters a turbine operating at steady state and expands adiabatically to 1 bar. The isentropic turbine efficiency is 92%. Employing the ideal gas model with k=1.4 for the air, determine (a) the work developed by the turbine, in kJ per kg of air flowing, and (b) the...
  7. M

    Uncovering Fusion Efficiency: Comparing Fusion and Fission in Energy Conversion

    The efficiency to which I am referring is the amount of mass converted to energy. I need to find an academic source to cite that fusion is more efficient in this respect than fission. Any sources?
  8. V

    Is a constant velocity the most efficient way to drive a car?

    I've read (I think it was on slashdot) that using constant velocity cruise control on your car is much more energy efficient than letting your speed vary. To the point where they said you would want to control your speed to much less than 1 kph. What is the general consensus on this? I'm a...
  9. Loren Booda

    What is the maximum shortening of a string after tying an overhand knot?

    Given a flexible, inelastic and incompressible string of radius R, how much at most would it shorten from tying an overhand knot in it?
  10. L

    How to measure inverter efficiency

    set up 12v bat. to 150w inverter to a tower pc. so i put a amp meter between 12v bat and inverter .times the volts by amps get wattage? then get the wattage of computer using a mains socket(because the inverter produces modified sinewave and my wattage meter may not work...
  11. M

    Heat,work, thermal efficiency problems

    This is the question that I can't really answer 1. A cycle looks like an ellipse in the T-S diagram. The maximum and minimum temperatures are 1000K and 400K. The maximum and minimum entropies are 0.705 KJ/K and 0.235 Kj/K. Determine a. the heat added per cycle, b. the work produced per...
  12. G

    Cogeneration (CHP) engine electrical efficiency

    Hello to you all, Does anyone know if gas engines running on a cogeneration (combined heat & power) mode can achieve electrical efficiency rates as high as 40% as it is...
  13. B

    Building a tester for solar cell efficiency

    I am trying to have students build a tester with sourceMeter, lamp, etc. for solar cell efficiency measurement. Could someone give me advice on this project? Thank you very much.
  14. T

    Turbine Efficiency: Calculating Power & Combined Efficiency

    Homework Statement I have attached the question. I'm not really sure how to do this one Homework Equations power = work done/time The Attempt at a Solution Is the turbine efficiency simply the power generation (750kW) divided by the mechanical output (800kW) which is so 750/800 x...
  15. E

    Efficiency of a DC Motor Gearbox

    Does the efficiency of a gearbox just reduce the torque output of the motor? Or does it also reduce the speed? For example I have a motor with 100 N*m torque at 100 RPM, it then goes into a gearbox with a 80% efficiency and a 2:1 ratio. So the torque would be 2*100*0.8 Nm and the RPM 100/2...
  16. P

    Measuring Efficiency of Fuels with Physics, Chemistry and Biology

    Hi, I am working on this project that has to involve physics, chemistry and biology. The chemists in my group will be performing an experiment to measure the enthalpy of combustion of three different fuels: alcohol, diesel and petrol. My task as a physicist is to, using their results...
  17. C

    Guard band allocation and spectral efficiency

    HI, I am wondering what factors go into spectral efficiency and determining and calculating guard bands. Could a tunable antenna or filter within a handset reduce the necessary size of a guard band thereby increasing a networks spectral efficiency? How are guard bands determined/defined and...
  18. N

    Engineering Shaft speed of a motor at 80% efficiency

    Homework Statement A motor produces 1000kW of power, running at 1500rpm. What is the running speed if it runs at 80% power? Homework Equations None that I know of. You can find the torque by the below equation (but again, I don't know how to deal with the 80%) P = \frac{Tn}{9549}...
  19. J

    Heat to current conversion efficiency

    Does anybody have any numbers for this new discovery? http://web.mit.edu/newsoffice/2011/sun-free-photovoltaics-0728.html How much of the heat is converted into electricity by a standard thermoelectric power plant? And how much of the heat is converted into electricity by this new device?
  20. B

    Does the Silver Wire Net Really Increase Gas Range Efficiency?

    There are rumors circulating recently on various forums on the internet that a net made of coiled up silver wires increases the efficiency of a gas range when placed on top of the gas burner while fuel is being burned. According to what manufacturers claim, this is done by using the reaction of...
  21. B

    Second Harmonic Generation: Light Intensity & Efficiency

    OK so i know it is possible to double the frequency of a light beam by using second harmonic generation by passing the beam through a non-linear crystal; however i am unclear as to the required intensity of light beam that is needed to achieve efficient conversation. Would it be possible to...
  22. G

    How Does Pulley Size Impact Efficiency in Large Scale Lifting Systems?

    If one was to make a pulley to lift something massive like a ship, I am assuming the masses involved of the ship and the counterweight, will mean decreased efficiency due to : 1. Higher friction between in the sheave and axel area. 2. larger cable/robe mass on the longer end (once the pulley...
  23. S

    Nextgen SSOlar, Efficiency, Broadcast Power

    Would the efficiency gained in an orbital Solar generating facility be mitigated by some/degree of diffusion loss when transmitting, say by microwave. through an atmosphere? Is the rate of efficiency growth in solar panels comparable to that of computer chips? (I think the answer is no). And...
  24. K

    News How can we improve the efficiency of our penal system?

    I know people from countries where they just shoot the bad guys. Not much for trials & justice. We spend a lot on housing prisoners in the US. How can the efficiency be improved? Disclaimer: sorry for not creating yet another left-vs-right thread.
  25. R

    Hacked off with college over Velocity Ratio and Efficiency question.

    Homework Statement If the work put in is 3000j, calculate the useful energy output. [PLAIN]http://www.mkwebman.com/question Load = 1962N Homework Equations VR = Distance covered by effort / Distance covered by load MA = load/effort Efficiency = MA / VR Efficiency = useful...
  26. A

    How Is Thermo Efficiency Calculated in a Monatomic Gas Cycle?

    Thermo Efficiency question! Homework Statement Figure P22.53 represents n mol of an ideal monatomic gas being taken through a cycle that consists of two isothermal processes at temperatures 3Ti and Ti and two constant-volume processes. For each cycle, determine, in terms of n, R, and Ti ...
  27. A

    Biofuel Subsidies and Viability: Examining the Controversy

    I note there was talk in the USA about ending the subsidies> There is a link here:- http://www.mcphersonsentinel.com/news/x2108616414/Fight-over-ethanol-brewing-in-D-C Also here:- http://www.afdc.energy.gov/afdc/laws/law/ND/5865 A licensed fuel supplier who blends biodiesel or...
  28. F

    Nuclear Fusion and Nuclear Fission, safety and efficiency

    Hello, I am doing a small research investigation into whether Nuclear Fusion will provide a safer and as efficient energy source as current Fission technology. Just interested if anybody has opinions on the topic and what their stance is on Nuclear Fusion, do they think it can work, any...
  29. A

    Calculating the Efficiency of a Reversible Refrigerator

    Homework Statement A reversible refrigerator has a coefficient of performance equal to 9.55 What is its efficiency? Homework Equations COP = Qh/W e = W/Qh The Attempt at a Solution I thought e would simply be 1/9.55 = 0.1047 =0.105 (Sig. fig) This answer was incorrect...
  30. J

    Efficiency of the heating process

    120MJ of heat are used to heat up a 1100kg component from 22oCelsius to 180oCelsius, in 1 hour, prior to heat treatment. If the specific heat capacity of the components material is 500J/kg, calculate the efficiency of the heating process. Please could somone give me the equation that i need...
  31. J

    Rocket Propulsive efficiency at lift off

    According to Wikipedia: http://en.wikipedia.org/wiki/Propulsive_efficiency the propulsive efficiency of a rocket is at its peak when the rocket is traveling at the same speed as it is ejecting its exhaust. I understand that, but the graph (and equation) on that Wikipedia page (and elsewhere on...
  32. C

    What is the efficiency of the Sun, really?

    Does all (i.e. 100%) of the energy generated in the Sun's core via nuclear fusion eventually escape out into space (as photons, neutrinos, ... and umm solar wind?), or is some energy lost to internal processes? Surely the photons must lose energy as they take their long, indirect path from the...
  33. O

    Electron Ionisation: Electric Field Interaction & Efficiency

    In electron ionisation, how does the electron beam transfer energy to the molecule being ionised? Is it via the interaction of the electric fields of the electrons in the molecule and the beam? If so, what type of interaction? And why is ionisation efficiency of the beam maximised when the...
  34. J

    Suggestions on Improving Efficiency (Motor-Generator)

    (Drawing of the setup attached) Background: We conduct electrical tests in our lab on electrical components (circuit breakers, switchgears,etc). In the lab we have a short-circuit Generator that generates the electricity for the tests. The generator is powered by an asynchronous motor...
  35. F

    Why does the Rankine cycle require the condensation of water before reheating?

    In a Rankine cycle such as a steam power plant, why does the liquid (water) have be condensed before being reheated first? Isn't the Q just extracted during the condensation stage, wasted into a nearby reservoir, and then re-added in the boiler? Could this water not be fed straight to the...
  36. P

    Why Is a Turbine More Efficient in Winter?

    Hello, An electrical power station situated in Northern Canada uses water to cool the steam as it leaves the turbine. Suggest why the efficiency of the turbine would be greater in winter than in summer: I first started to think in terms of the efficiency equation I have for heat engines...
  37. S

    Efficiency of electric generator in the vacuum of space?

    I was just thinking that if you set something spinning in space it keeps turning, so does this mean once you started an electrical generator turning would you get ‘free’ energy?? Will the force from the magnetic field eventually case the wire to stop spinning?
  38. Femme_physics

    Energy conversion efficiency of electric heaters is 95%? Shouldn't it be a 100%?

    The excuse given to why energy conversion efficiency even exists, is because that some of the energy is converted to heat. Then how come in electric HEATERS not all the energy is converted to heat? To what does the rest of those 5% is being converted to...
  39. mcodesmart

    Solar Panel Efficiency: Temperature Effect

    Does the temperature of a solar panel decrease its efficiency?
  40. K

    Engineering Series Motor, what is the efficiency?

    I have worked this particular problem many times and I keep calculating a power in P(in) that is smaller than calculated power out P(out), resulting in an impossible efficiency of >100%. Is there a mistake in the problem or in my work? Homework Statement A 20 hp, 230 V, 1800 rpm DC...
  41. N

    Efficiency of a heat engine at high temps

    Homework Statement What is the maximum effciency of a heat engine whose operating tempuratures are 550oC and 365oC? Homework EquationsE=1-Thot/Tcold The Attempt at a SolutionPLEASE HELP! My thinking is that the effciency is equal two one minus the temperature in the hot resavour...
  42. F

    Verifying Efficiency in a Thermodynamic System: Q1 & Q2

    Homework Statement http://i754.photobucket.com/albums/xx183/reddiesel08/Q2.jpg Homework Equations e = 1 - (Tc/Th) (Temp in Kelvins) The Attempt at a Solution e = 1 - (300k/520k) = .42 or 42% No because the engine can only perform 42 J of work for each 100 J of energy. Homework...
  43. I

    Maximizing Efficiency in Automobiles: Defining and Improving Performance

    Homework Statement I am in grade 11 physics and we are learning efficiency, Eout/Ein.. stuff like that. I just have a few questions about cars: How is efficiency defined in cars and why is it so low in cars? What/How are we improving efficiency? The Attempt at a Solution I think that it...
  44. I

    What Modifications Can Boost Ramp Efficiency Without Height Adjustment?

    Homework Statement We have a lab in which there is a ramp with one end on the floor and the other end is on top of a few textbooks. Therefore, it has a slope, and an object is lifted using the ramp. What can we do to this set-up to increase the efficiency, OTHER THAN INCREASING THE HEIGHT...
  45. I

    Efficiency What makes it less than 100%?

    Homework Statement List a couple factors that make efficiency less than 100%. Homework Equations Efficiency = Eout / Ein Eout = mgh Ein = Work = FD The Attempt at a Solution IDK :\
  46. I

    Archived Mechanical Efficiency of a Ramp

    Homework Statement We have to find the efficiency of a ramp for a lab. We are given an inclined plane, a wooden block and a few masses. We are also given a Newton spring scale. Homework Equations efficiency = (Eout/Ein)*100% Eg = mgh Work = FD The Attempt at a Solution Is the...
  47. I_am_learning

    LPG Efficiency Booster - 25% Fuel Savings!

    I got one device that is small and in ring shape. You have to pass your LPG pipe through the hole and before reaching the stove. It is said that it improves fuel economy by around 25%. The device is Mostly Magnet (can't see inside, but it pretty strong Magnet). Any possibility?
  48. S

    Total Efficiency in Parallel Transmissions

    I'm trying to figure out an expression for the total power efficiency from engine to wheel of a parallel transmission in terms of the efficiency of all the components in between (i.e. spur gears, motors, pumps, etc.) such that P_{engine} = \eta(\eta_{i})*2P_{wheel} See attached image.
  49. M

    Maximizing Efficiency in Tandem Carnot Engines

    Please help with the following: Prove that the efficiency of two carnot engines operating in tandem, one going from a cold reservoir of temperature Tc to a hot reservoir of Ti, then the second going from a cold reservoir of temperature Ti, to a hot reservoir of temperature Th must be less than...
  50. P

    Calculating the Efficiency and Speed of a Toy Train

    A 0.50 kg battery-operated toy train moves at a constant velocity of 0.30 m/s along a level track. The power developed by the motor is 2.0 W and the total force opposing the motion of the train is 5.0 N a) Calculate the efficiency of the train's motor b) Assuming the efficiency and the...
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