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

    Can Refrigerators Have Greater Efficiency Than Theoretical Value?

    Homework Statement the efficiency of a fridge is given by n=Q/W but this is actually the coefficient of performance. normally the efficiency of an engine is n= W/Q. the result i get for the coefficient of performance is 18.5 and my textbook says real fridges have coefficients of 4 or...
  2. J

    Heat production from low wear friction - efficiency

    heat production from low wear friction - efficiency What are some efficient methods of producing heat from low wear friction? Regards
  3. smokingwheels

    Calculate Thermal Indicated Thermal Efficiency Of An Otto Engine

    Homework Statement What is the indicated thermal efficiency of an engine? Fuel used in total 42.61 cc/min @ 1730 rpm. Fuel used to get to 1730 rpm = 29.16 cc/min no load. Fuel left = 13.45 cc/min to do approx 4.335 kw at 1730 rpm approx 40.95 kph Fuel heat content 34.8 kj/l...
  4. Y

    Can a Wired System Achieve 100% Efficiency?

    I was discussing solar cells with my friend and we began talking about law of diminishing returns when once a light is lit up, it will send some of the light to the solar cell and energy back into the bulb. When it goes back to the bulb, it won't have as much energy as it did to light the bulb...
  5. S

    Calculate Work, Isentropic Head & Efficiency of a Centrifugal Gas Compressor

    Hi everyone! I have a question and I would be so thankful if you could help me! For a Centrifugal Gas Compressor, if I have the flow rate, the input and output temperatures and pressures in specified rpm, then could I calculate its needed work, isentropic head and efficiency? how? Thanks! Sara
  6. M

    The Efficiency Loophole: A Local Hidden Variables Theory?

    If we assume that an electron in an entangled pair has more than 2 plans (plans that determine if an electron go up or down through a magnet) to choose from, can we create a local hidden variable theory? If this is true, how many plans to choose from would an electron need for this to work...
  7. L

    Power - Calculate Efficiency

    An 8.5x10^2kg elevator is pulled up at a constant velocity of 1.00m/s by a 10.0kW electric motor. Calculate the efficiency of the motor. Efficiency = work out/work in * 100 How do I calculate "work out/work in" using the information given?
  8. smokingwheels

    Heat engine efficiency calculation

    Homework Statement I have an spark ignited engine and after modifying it I have improved the efficiency. What is its efficiency at idle? Fuel consumption at 650 rpm = 9.8 cc/min measured Fuel consumption at 750 rpm for normal engine = 25-30 cc/min estimated for about 5 HP Normal engine...
  9. A

    Low Air in Tires: Impact on Fuel Efficiency

    Homework Statement Why does a car uses more fuel with lesser air in tyres? Homework Equations Work done =F.d The Attempt at a Solution According to me Friction does no work in rolling if the tyre is purely circular. But when tyes are deflated then they are not circular. Due to...
  10. M

    Calculating Efficiency of Otto Cycle

    My team has recorded information on a single cylinder Otto cycle from a lab we have done. We are supposed to compare the theoretical efficiency of the cycle to the experimental efficiency. Using a given compression ratio of 3 and the ratio of specific heats for the fuels we used we were able to...
  11. C

    Engine Efficiency: 1.4 kg Gasoline/hr = 3.5 kW Power

    Homework Statement An engine burns 1.4 kg of gasoline per hour and yields 3.5 kW of power. Homework Equations Calculate the efficiency of the engine when the heating value of gasoline is 43 MJ/kg. The Attempt at a Solution Plz i just need the rule for engine efficiency.
  12. G

    Color\Light efficiency in imaging systems

    In making comparisons on efficiency in acquired ambient light for imaging devices, whether they be CCD and CMOS cameras or reflective displays, it seems the factoring is always based on Red, Green and Blue as if those are the only bands of visible light. For example, in acquiring\reflecting the...
  13. S

    Comparing Energy Efficiency of New vs Recycled Paper

    How i am going to compare energy efficiency between new paper and recycle paper ? in order to compare them, i have to convert all the energy require in those process into the same unit right ? By using Joule ? or ?
  14. M

    MATLAB Improving MATLAB Array Efficiency

    Hi all, I have the following code: M = zeros(N) for i = 1:N for j = 1:N M(i,j)= log(norm(rs(:,i)-rc(:,j)))+log(norm(ri(:,i)-rc(:,j))); end end Where rs, rc and ri are 2xN arrays. Is there a way to construct the matrix without the use of the two for loops? I'm...
  15. A

    Heat engine/thermal efficiency question

    Homework Statement The figure shows the cycle for a heat engine that uses a gas having gamma =1.25. The initial temperature is T1=300K, and this engine operates at 20 cycles per second. What is the engine's thermal efficiency...
  16. J

    Efficiency of a heat engine in a reversible cycle

    Homework Statement A heat engine operates in a reversible cycle with the following steps: (i) An ideal gas characterized by γ = 1.4 expands adiabatically, so that it cools from an initial temperature of 330°C to 30°C. (ii) It is compressed isothermally until it reaches its initial volume...
  17. B

    Efficiency and the Euclidean Algorithm

    1. Question Let b = r_0, r_1, r_2,... be the successive remainders in the Euclidean algorithm applied to a and b. Show that every two steps reduces the remainder by at least one half. In other words, verify that r_(i+2) < (1/2)r_i for every i = 0,1,2,... 2. Attempt at a solution I take an...
  18. N

    Increasing Fuel Efficiency through Propeller Upgrades

    Hello, I am looking into ways to increase the fuel efficiency in a various number and type of ships, with engines running from diesels to steam plants to gas turbines. I was wondering where I might find information on the state of the art practices with propeller design. Specifically...
  19. T

    What is the thermal efficiency of an ideal gas cycle?

    Homework Statement A possible ideal gas cycle operates as follows: (i) From an initial state (p_1,V_1), the gas is cooled at constant pressure to (p_1,V_2); (ii) the gas is heated at constant volume to (p_2,V_2); (iii) the gas expands adiabatically back to (p_1,V_1). Assuming...
  20. B

    Energy Conversion Efficiency of EL Wire

    As lighting decorations, EL wires that use an alternating current to make a phosphorous material radiate light are said to be very efficient and generate little heat. But what exactly is the energy conversion efficiency of such a device expressed as the ratio of output radiative power divided by...
  21. P

    How to calculate the efficiency of an amplifier?

    How to calculate the efficiency of an amplifier e.g. op-amp? Been thinking about that, and have no answer. It should not be Vout / Vin ?
  22. V

    Calculate compressor efficiency

    Hello I am struggling with how a compressor's efficiency is calculated. This is the set up: I have a Garrett T3 compressor housing being spun by an electric motor. I can measure the airflow in, the airflow out, the pressure and temperature on both sides of the compressor, the power...
  23. J

    Rocket fuel efficiency and payload capacity rule of thumb

    "A rule of thumb is that for every ten-percent increase in efficiency for rocket fuel, the payload of the rocket can double.” Can someone assist me with a simple formula to model this rule-of-thumb? What happens to the payload if the rocket fuel efficiency increases twenty to thirty percent?
  24. H

    The efficiency of a vehicle engine

    Homework Statement A vehicle engine has a power output of 6.2 KW and uses fuel which releases 45 MJ per kilogram when burned. At a speed of 30ms ^-1 on a level road, the fuel usage of the vehicle is 18km per kilogram. Calculate: the useful energy supplied by the engine in this time...
  25. B

    Maximum labor efficiency without unemployment

    How few jobs would it take to run a perfectly efficient economy and how many people could that economy sustain? For argument's sake, let's choose an arbitrary number, say 1 million people, to run mass-production factories and other essential sectors. If this number of workers could supply a...
  26. S

    How does the gear ratio affect the power efficiency generated by a wind turbine

    I have a basic question on how the power efficiency of wind turbine affected by the gear ratio. Suppose there is a generator connected with the rotor through a gear enhancer, a higher angular speed of generator is obtained. Since a higher voltage is produced, we may think that the power...
  27. L

    Efficiency & Leakage in non-circular solenoid cores

    Part of a new product we're designing needs a small iron-core D.C. electromagnet for an actuator. I designed the electromagnet's core to be circular: about 4.5mm in diameter with 200 Ampere-Turns in the coil. An axis-symmetric FEA showed the iron core to be near saturation, and producing a...
  28. K

    Which Temperature Adjustment Improves Carnot Engine Efficiency More?

    Homework Statement Determine which gives the higher efficiency of a Carnot engine, increasing the temperature of the hot reservoir, or decreasing the temperature of the cold reservoir by the same amount. Justify your answer carefully. Homework Equations (TH-TC)/TH)The Attempt at a Solution By...
  29. L

    Optics: Designing a coating to enhance detection efficiency

    Homework Statement You are to design a coating to enhance the detection efficiency of a silicon detector (n=3.42 at \lambda=351nm) (a) Is the coating a reflection or antireflection coating? (b) Should you use a higher or lower index material for the coating? Specify a material to use. (c)...
  30. L

    Optics: Designing a coating to enhance detection efficiency

    Homework Statement You are to design a coating to enhance the detection efficiency of a silicon detector (n=3.42 at \lambda=351nm) (a) Is the coting a reflection or antireflection coating? (b) Should you use a higher or lower index material for the coating? Specify a material to use. (c)...
  31. J

    Refrigerator COP to Efficiency

    Homework Statement The question is simply: A reversible refrigerator has a coefficient of performance equal to 13.8. What is its efficiency? Homework Equations COPrefrigerator = Tc/(Th - Tc) Efficiency = (Th - Tc) / Th The Attempt at a Solution I'm assuming I need to use these equations to...
  32. T

    Compression Ratio Connection to Efficiency

    Hi. I was wondering if anyone had ever done a relationship analysis of compression ratio in relationship to efficiency. I have heard that higher compression ratio can often relate to efficiency, but I was hoping to find some kind of graph correlation on it, however I haven't been able to find...
  33. P

    Efficiency of solar panels: Earth vs Space

    First of all, if this should have went in the Engineering section, I'm sorry... I wasn't sure where to write this post. If a solar panel on Earth's surface can gather say 100W/m^2 in full sunlight, how much would the same solar panel be able to gather in space, outside of Earth's atmosphere...
  34. A

    Maximizing Efficiency in Two-Dimensional Packing: A Comprehensive Guide

    There is this school project on efficiency in packing but i can't actually find any good data . The main idea is the amount of goods that can be fixed in a place but i want it in just 2 dimentions. It has to be related to area and not to volume as that becomes too complex. Any help in...
  35. J

    Alternator efficiency question

    Hi guys, Currently just looking through a few concepts for wave energy converters and I noticed that a few designs use bi-directional rotating turbines (or linear action) meaning the alternator has to continuously keep rotating in one direction, stopping, rotating in the other direction...
  36. S

    Exploring SCRAMjet Design Proposals and Efficiency

    So I was wondering if there was only one generally accepted SCRAMjet design or if there are many. Based on the small amount of info available, info primarilly concerning theoretical hypersonic operation, it seems that most design proposals involve a "physical" compression of air in the inlet...
  37. A

    Maximum Efficiency of a Solar-energy Panel

    Homework Statement The maximum efficiency of a solar-energy panel in converting solar energy into useful electrical energy is currently about 12 percent. In a region such as the southwestern United States the solar intensity reaching Earth's surface is about 1.0 kW/m2 on average during the...
  38. R

    Why is gasoline preferred over diesel for cars?

    even though the thermal efficiency of diesel engine is more than that of gasoline engine , why is it that gasoline is preferred over diesel for cars?
  39. S

    Can IC engine efficiency can be increased beyond 60% ?

    I found following claim from an inventor: “The limit of IC engine efficiency cannot be normally exceeded due to facts entropy cannot be decreased and 2nd law of thermodynamics (heat cannot flow from cold to hot body). Injecting water in the beginning of expansion stroke can overcome these...
  40. T

    Please help to check the efficiency of renewable energy system design

    Hello experts, Please help to verify the attched design of renewable energy system which uses combination of gravity and buoyancy forces for power generation. I am looking use balls of 10c.m radius and water column of 10m hight. It will be very helpful some experts could advice me on how...
  41. J

    Efficiency of an ideal-gas cycle.

    Homework Statement A possible ideal-gas cycle operates as follows: (i) from an initial state (p1,V1) the gas is cooled at constant pressure to (p1,V2); (ii) the gas is heated at constant volume to (p2,V2); (iii) the gas expands adiabatically back to (p1,V1). Assuming constant heat...
  42. P

    How is the total energy output of a power plant affected by its efficiency?

    Basic efficiency question... Basically, the question says that efficiency of a power plant is 62%, and that the plant produces 1 GW of electricity. Now, would this mean that the total energy produced by the plant is 1/0.62 G Joules/ second? Or would the 1 GW figure be the total energy produced...
  43. H

    Calculating Propulsive Efficiency of an Aircraft Propeller

    An aircraft is flying straight and level at a speed of 150 mph. Its propeller has a diameter of 8 ft and is generating 300 lbf of thrust at an altitude of 3000 ft. What is the propulsive efficiency of the propeller at this operating point? no equations given, but from searching around I've...
  44. C

    Thermodynamic/Carnot efficiency

    Homework Statement A novel heat engine is being considered for producing work from the thermal energy contained in the wastewater discharge from a large food processing plant. On an average day, 35 degree celcius wastewater leaves the plant at and is discharged into the ocean at 1,000...
  45. A

    How can acceleration affect fuel efficiency in a 1991 Geo Metro?

    Greetings everyone! Just a few weeks ago, I got it in my head that I'd like to determine some formulas for the efficiency of an engine - particularly mine, a 1991 Geo Metro. The overall goal is to compare various acceleration rates to show how slower acceleration can produce greater gas...
  46. D

    Does the Launch Angle Affect Efficiency in a Slingshot?

    I need to explain why, in our tests, the efficiency of our slingshot device remained constant when the angle of launch was changed and the extension (how far the rubber band was pulled back) was constant. Basically it was a 1m long wooden plank held up on bricks, with a rubber band attached...
  47. G

    Ideal thermal efficiency impossible?

    I know a heat engine can never be 100% efficient. There has to be a cold reservoir that some of the heat is rejected to. Why is that? I know it is because of entropy, but could someone please provide some further explanation. Thanks.
  48. D

    Measuring Projectile Efficiency: Is 51% Accurate?

    Hi, I have a rubber bouncy ball which is shot off a ramp using a rubber band slingshot. I've calculated the ideal range, and then measured the real range. By dividing the real by ideal and multiplying by 100, I get a 51% efficiency. Does that sound viable? How else can I measure the...
  49. G

    Why is 100% efficiency impossible for heat engines?

    My question involves heat engines. I understand that a heat engine typically uses energy provided in the form of heat to do work. According to the 2nd law of thermodynamics, however, not all heat energy can be converted into work energy, meaning that heat engines are not perfect. At least some...
  50. P

    Carnot cycle with efficiency > 1

    Is it possible (at least theoretically) to construct engine which uses Carnot cycle and two reservoirs with temperatures T_1<0<T_2 (one of them has negative temperature which is possible e.g. in case of two-state paramagnet). Such cycle would have efficiency greater then 1. (of course the...
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