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. L

    How does inclination affect the efficiency of a ramp?

    So I did a lab experiment and found out that the higher the angle, the more efficient the ramp is, and just curious, does anyone know the reason for this? Any info provided would be greatly appreciated.
  2. L

    Expansion Volume of n-Pentane as Working Fluid & Carnot Efficiency

    Greetings Engineers & Scientists. This is my first post. I'm an accountant so excuse my ignorance. See diagram attached. I want to calculate how much volume expansion there would be if we vapourised n-pentane. I did this experiment with air (on a smaller scale) but there was not much...
  3. S

    Problems with solar cell efficiency

    As the solar cell gets further away from the light source, does it get more efficient or less efficient? At the moment I am able to work out how much power enters the solar cell. However, it is pretty weird because as I found out from my experiment, the efficiency of the solar cell gets better...
  4. J

    Isentropic efficiency vs polytropic efficiency of a gas turbine

    definition wise i got the difference between these two efficiencies. but in practice how does these two differ? i was referring to this book: Jet propulsion: a simple guide to the aerodynamics and thermodynamic design ... By N. A. Cumpsty he has mentioned this: "using polytropic...
  5. V

    How Much Energy Input Is Needed for an Engine to Perform 10.2 kJ of Work?

    Homework Statement A heat engine operating between 78.5oC and 204oC achieves 20.6% of the maximum possible efficiency. What energy input will enable the engine to perform 10.2 kJ of work? The only help I need with this is exactly what equation(s) to use. I would think thermal efficiency...
  6. J

    Efficiency of Rankine Cycle Using R141b - Confirmation Needed

    I've just completed a lab session on the Rankine Cycle using R141b as the working fluid and have obtained some values for the different effciencies in the cycle. I have that; ηTheoretical =13.01% ηPractical =12.07% ηIsentropic =5.90% I'm pretty sure I've followed the lab sheet correctly...
  7. D

    Is there any law that states something cannot have 100% efficiency?

    I understand that all real-world applications can never attain 100% efficiency, whether it be referring to something mechanical, electrical, or some thermodynamic cycle. While studying the Carnot cycle and learning about the upper limit of efficiency for thermodynamic cycles, I drew a blank...
  8. N

    Calculate Efficiency of Particle Production

    Homework Statement Derive the efficiency for production of a particle of rest mass m made by colliding a 'bullet' particle of mass M with a stationary target particle mass N. Homework Equations ans is k^-1 =1 + (m+2M)/2N The Attempt at a Solution \bf{P_1} + \bf{P_2} =...
  9. 1

    Calculate the efficiency of the electric motor.

    Homework Statement An 8.5 X 10^3 kg elevator is pulled up at a constant velocity of 1m/s by a 10kW electric motor. Calculate the efficiency of the electric motor. Homework Equations P=w/t %efficiency=work out/work in X 100% W=mgh d=vit+1/2at^2 v=d/t The Attempt at a Solution The...
  10. K

    Solve Energy Needed to Raise 2000kg Lift to 10m

    Homework Statement A engine used to raise a lift is 60% efficient, and the lift's mass is 2000kg. How much energy would be needed to raise it to 10m?Homework Equations Efficiency = energy output/ energy input *100 The Attempt at a Solution EP=mgh = 2000*9.8*10= 196000 J. Therefore, eff...
  11. T

    Quick Question- carnot efficiency

    Suppose an engine uses multiple heat reservoirs: When calculating the carnot (maximum possible efficiency) is it valid to simply take the average of the temperatures of the hot reservoirs from which the heat is extracted as T(hot) and the average of the temperatures of the heat sinks to which...
  12. L

    Efficiency of Carnot Engine Question

    Homework Statement This is from "Equilibrium Statistical Physics" by Plischke and Bergerson, problem 1.1: "Consider a Carnot engine working between reservoirs at temperatures T1 and T2. The working substance is an ideal gas obeying the equation of state [ PV=Nk_BT ], which may be taken to be...
  13. J

    Calculating Efficiency of an Inclined Plane

    Homework Statement A washing machine that weighs 1400N must be put into a delivery truck bed that is 1.2 m off the ground. A worker uses a force of 450N to push the machine up a ramp that is 4.3m long. What is the efficiency of the inclined plane?Homework Equations e=(MA/IMA)100---- efficiency...
  14. S

    Efficiency with a combustion engine

    I've been trying to understand why fuel economy decreases when the engine gets into higher RPMs. That is, if you put the pedal to the metal and quickly accelerate to 40 MPH, your engine operates much less efficiently than if you slowly accelerated to 40 MPH. Here's where it seems the...
  15. V

    How calculate propeller efficiency if I know propeller trust?

    How calculate propeller efficiency if I know propeller trust ant motor power and motor efficienty?
  16. C

    Measuring Gas Mileage Efficiency in Using the A/C, Rolling the Windows Down

    I'm not using the template because this is a rather abstract question about the way to approach a scientific experiment. I'm beginning a science project in which I hope to define the speeds at which using an air conditioning unit becomes more efficient than rolling the windows down in a car...
  17. B

    Power cycle efficiency problem

    Homework Statement A power cycle has a thermal efficiency of 40% and generates electricity at a rate of 100 MW. The electricity is valued at $0.08 per kW * h. Based on the cost of fuel, the cost to supply Qin is $4.50 per GJ. For 8000 hours of operation annually, determine, in $. a. The...
  18. J

    Photoelectric efficiency and subatomic (ie electron or hole) momentum

    Homework Statement The efficiency of electron excitement by photons is described as being related to how much different orbitals share the same k-space or momentum space. Is this similar to orbital shape (eg spheres, dumbells, ec)? Homework Equations The Attempt at a Solution I...
  19. R

    PC Cell Efficiency: Find Power (in W)

    Homework Statement A photovoltaic cell has area 80 sq cm and efficiency converting energy in the form of sunlight to electricity of 7%. The sun's intensity is 800 W / sq m and the rays are perpendicular to the cell's surface. What power will be produced by this cell (in W)? Take care in...
  20. A

    Efficiency of electrical power plant

    Homework Statement An electrical power plant manages to transfer 88 percent of the heat produced in the burning of fossil fuel to convert water to steam. Of the heat carried by the steam, 40 percent is converted to the mechanical energy of the spinning turbine. Which best describes the...
  21. M

    Carnot Engine: Efficiency, Law of Thermodynamics, 6 Stroke

    the carnot engine does not obey any law of thermodynamics,because it has 100% efficiency,now do we have any engine that has come close to this hypothetical engine?(in terms of efficiency ) can this process of carnot be used for a 6 stroke engine?(hypothetically)
  22. A

    Generator Efficiency: Learn About RPM Impact

    Hey, I was wondering if someone could link me to a good source where I can read about electrical generator efficiencies and how they relate to RPM. I tried doing some derivations myself and came up with a somewhat believable result, but am not ready to trust myself as this is far outside my area...
  23. Spinnor

    Thermodynamic efficiency of small diesel engines.

    Could a 10 HP diesel engine be made as fuel efficient as say a 100 HP diesel engine, that is (work done/fuel used). Does thermodynamics prevent a smaller engine from being more efficient? Thank you for your time.
  24. B

    Auto/Motor Diy measurement of car efficiency

    It seems to me a typical gasoline car has wastes about 95% of the gasoline energy before any rotating energy gets to the wheels. Here's my reasoning. I once measured my cars efficiency (an old Renault 5). I drove 100 km/h (28m/s) on a flat and level freeway, with no wind, and set the gears...
  25. K

    Determine the isentropic efficiency of a turbine

    Homework Statement Neon gas at the rate of 100kg/min enters an adiabatic turbine at a temperature and pressure of 1073K and 1.5 MPa. The gas leaves the turbine at a pressure of 200kPa. If the real(actual) power output of the turbine is 370 kW, determine the isentropic efficiency of the...
  26. D

    Calculating efficiency of a boiler

    Hi, I've been attempting this problem all week now and I can't seem to even begin to obtain an answer which is highly frustrating, so here's the problem: An electric boiler is required to raise the temperature of 90 litres of water per hour by 35oC. If the input required to affect this...
  27. C

    Max Efficiency of a Carnot Engine vs Other Engines

    quick question, is the difference between a carnot engine to an engine is that the engines eff is less than or equal 1-(cold temp / hot temp), and the carnot is the max of this which is just equal 1-(cold temp / hot temp)?
  28. 2

    Quantum Efficiency Mapping setup for solar cell charatcerization

    In order to build a QE measurement system, I want to confirm the following issues: (1) Is collimated light required for QE characterization of the entire solar cell? How "bad" it could be if having Gaussian beam? (2) It seems LBIC is most common for QE mapping. Is it possible to use...
  29. Topher925

    Is the quantum efficiency of a photodiode dependent upon its temperature?

    Like the title states, is the voltage produced by a photodiode, or any PV device for that matter, dependent upon that devices temperature? To rephrase, if you have a fixed amount of photons coming in contact with the business end of a photodiode, is the voltage or current generated by the...
  30. N

    Gibbs energy of formation and electrolysis efficiency

    Hello - I'm having some problems understanding Gibbs energy of formation, and how it's applied to electrolysis. So, I'm hoping someone can explain what I'm doing wrong.. According to his site: http://hyperphysics.phy-astr.gsu.edu/Hbase/thermo/electrol.html (image) The change in the Gibbs...
  31. A

    Efficiency of a Stirling Engine

    Homework Statement Derive an expression for the effiency of the cycle (of a Stirling Engine) working between two heat baths at temperatures T1 and T2 with volumes in the ratio V2/V1. Assume the working substance is a monatomic ideal gas. Homework Equations Work done=heat absorbed from...
  32. N

    Calculating Fan Power & Efficiency: What Data do I Need?

    Hi, How do I calculate the fan power (kW) and efficiency, given the flow rate, static/total pressure across the fan surface? Do I need more data? Thnx in advance.
  33. M

    Packing efficiency of particles in solids-space lattices

    I had to do an experiment in which I built examples of hexagonal closest packing, face-centered closest packing and a body-centered space lattice. I had to find the volume of a box that would fit tightly around them, and then calculate the density in units/cm3 (assuming a mass of 1 unit per...
  34. L

    How Efficient Is the Spring in Stopping a Rat on a Ski Slope?

    Homework Statement So, I have a 5.0 kg rat that goes down a ski slope, slides along a rough patch, and then smashes into a vertical board with a spring attached. I need to find out the efficiency of the spring with this information: m=5.0 kg v (after sliding across rough patch)=108 m/s ; it...
  35. N

    How Do You Calculate Transformer Efficiency with Given Power and Voltage?

    Homework Statement What is the the efficiency of a transformer with 13w of primary power. 120Vp, Np unknow 12Vs, 90Np Homework Equations The Attempt at a Solution eff= Psec/ Pri * 100
  36. M

    Power & Engine efficiency - Using heat (kelvin)

    Homework Statement 1. Homework Statement A power plant taps steam superheated by geothermal energy to 505 K (the temperature of the hot reservoir) and uses the steam to do the work in turning the turbine of an electric generator. The steam is then converted back into water in a condenser...
  37. M

    Engine efficiency - using heat (kelvin)

    Homework Statement A power plant taps steam superheated by geothermal energy to 505 K (the temperature of the hot reservoir) and uses the steam to do the work in turning the turbine of an electric generator. The steam is then converted back into water in a condenser at 323 K (the temperature...
  38. C

    Advising on Heat Pump Efficiency for 1500J at 280K

    Homework Statement The question asks us to advise the company on a heat pump (and give reasons) which is claimed to deliver 1500J to a room at 280K by consuming 50J of work per cycle pumping heat from the surroundings at 270K. I've drawn a diagram of the heat pump, taking heat Q2 from a bath...
  39. diegzumillo

    What Is the Efficiency of a Monoatomic Ideal Gas Cycle?

    Hello again, all! I have another basic thermodynamics question :P This one came from a 2008 admission test. Seems simple enough, but as usual, my answer doesn't match =P Homework Statement A monoatomic ideal gas performs, reversibly, the cycle shown in the diagram attached in this post...
  40. S

    Heat Engine - Maximum Efficiency

    Homework Statement A heat engine operates between a reservoir at 25 degrees Celsius and one at 375 degrees Celsius. What is the maximum efficiency possible for this engine? Homework Equations e = \frac{Qc}{Qh} The Attempt at a Solution I'm afraid that the equation above...
  41. N

    Engine Efficiency Cycle: 500K-300K, Isothermal Compression & Expansion

    process A: isothermal compression at low temperature with an input of work of 83 J process B: constant volume increase in pressure with an energy input by heating of 200 J process C: isothermal expansion at high temperature with work output of 139 J process D: constant volume cooling to the...
  42. kandelabr

    Maximizing Efficiency with a Continuously Variable Transmission

    I wonder what's the best efficiency that's possible to achieve with a continously variable transmission. I've googled a lot and can't find anything useful (with useful i mean an approximate value in [%]). thanks.
  43. C

    Increase the coupling efficiency of fiber

    I learn that increase of the beam size of the laser before coupling it to the fiber can increase the coupling efficiency of it. Can I know why is this so? Maybe the fiber is of very small diameter, and the focal lens in front of the fiber can't focus all the laser to this small diameter...
  44. S

    Efficiency of a 10%-Efficient Car Engine: Energy Transfer and First Steps

    A 10%-efficient car engine accelerates the 1700 kg car from rest to 18 m/s. How much energy is transferred to the engine by burning gasoline? What should be my first step in attempting this problem?
  45. T

    How Does Load Impact Electric Motor Efficiency and Speed?

    Does anybody know of an equation or rule of thumb for power decrease as load increases? As an example an electric golf cart will go say 15mph with one 100lb driver. Put 4, 200lb people in it and it will go much slower, say 9mph. Is there a way to determine what that loss will be other than...
  46. J

    Calculating Work and Thermal Efficiency of a Heat Engine

    Homework Statement A heat engine using 5.00 g of helium gas is initially at STP. The gas goes through the following closed cycle: - Isothermal compression until the volume is halved. - Isobaric expansion until the volume is restored to its initial value. - Isochoric cooling until the pressure...
  47. C

    How is coefficient of performance different from efficiency?

    Efficiency is essentially the ratio of what you get to what you put in. COP also seems to represents the same thing (i.e. COP of a refrigerator is Ql / W, which is the amount of heat removed / the amount of work done to remove it). I know efficiency cannot exceed 1, but how come COP can have...
  48. T

    What is the Efficiency of a Heat Engine?

    Homework Statement A hypothetical engine, with an ideal gas as the working substance, operates on the cycle shown in Figure 1. Show that the efficiency of this engine is e = 1 - \frac{1}{\gamma}\left(\frac{1 - \frac{p_3}{p_1}}{1 - \frac{v_3}{v_1}}\right) Where \gamma =...
  49. 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...
  50. 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?
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