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. A

    How much current does the elevator consume?

    Homework Statement Energy conversion efficiency of the elevator is 80%, it is working from 220 volts. How much current does the electro motor consume while it is constantly lifting the 500 kg cabin at 2 m/s. The attempt at a solution I=P/U, so I figured I need to know the power. P=F*v. I...
  2. A

    Electrical Efficiency Calculations HVAC

    Hi, I am trying to do a comparison of electrical efficiencies between 2 HVAC compressors but struggling to find formulas or calculations to figure it out. Can anyone help me?
  3. S

    Efficiency of a synchronous machine.

    Homework Statement The armature resistance per phase is given as 24.7ohms. Delta configured machine. Open circuit voltage is 220v, short circuit current is 1.1A at 3000rpm. Rpm is dropped to 1500rpm and no load line voltage is 100. Find power and efficiency if an inductive load of 1.4H is...
  4. zonde

    Efficiency model in loophole free photon Bell tests

    I would like ask comments about assumed photon detection efficiency model used in these experiments that test Bell inequalities and consequences if it does not hold. http://arxiv.org/abs/1511.03189 http://arxiv.org/abs/1511.03190 Detection efficiency is calculated as two-fold coincidence events...
  5. Recycler

    Wind turbine with increased efficiency

    Wind turbines apparently now produce electricity only at some minimum wind speed.In my conception,the wind pressure of a lower wind speed is used to exert a force on a diaphragm or vane which stores torque in a spring or other mechanism,This torque could be used to help overcome the initial...
  6. pioneerboy

    I How to determine an asteroid survey efficiency?

    I read in a couple of papers about asteroid hunting that they used artificially implemented asteroids in real images to see if their detection algorithms could find them. This way, the scientists determined their asteroid survey efficiency in real data. As I don't have the resources to work so...
  7. Guidestone

    AC Efficiency: Fact or Fiction?

    I've heard that alternate current is more efficient than direct current. I've heard is easier to transport than dc current. Is that true? Why is that? Also, why are three phase systems better than monophasic ones? Thank you very much!
  8. jdawg

    Isentropic Compressor Efficiency

    Homework Statement Nitrogen enters an insulated compressor operating at steady state at 1 bar, 310 K with a mass flow rate of 1000 kg/h and exits at 10 bar. Change in KE and PE is zero. Heat transfer is zero. Assume ideal gas with k=1.391. Find minimum theoretical power input required and the...
  9. H

    Energy Transformation Efficiency Problem

    Homework Statement A ball that weights 1kg is thrown in the air, the hand being 1m above the ground. The velocity the ball was thrown at was 14m/s and it's maximum height was 6.5m above the ground. What is the efficiency for this energy transformation? Homework Equations Do I just get the...
  10. L

    Fuel efficiency, turbine vs stroke generator

    Hi, I'm trying to figure which is more fuel efficient, turbine vs stroke generators. This honda stroke engine generator does 1000w for 3.8 hrs with 0.6 gallons of fuel or 2.3 liters, so the power per liter of fuel is 1,300 kW. http://powerequipment.honda.com/generators/models/eu1000i Then I...
  11. A

    Calculating work heat, and efficiency given a TS diagram

    Homework Statement Is it possible to calculate the work done heat transfer, and efficiency of an object in a thermodynamic system, given the Temperature vs Entropy graph? Example: Homework Equations ∆U=Q-W ∆S=dQ/T e=1-(Qc/Qh) e=W/QhThe Attempt at a Solution Since this is a T vs S diagram,i...
  12. K

    Understanding Carnot Efficiency

    I'm struggling to understand the Carnot efficiency. I can follow proofs that prove efficiency= 1- (Th/Tc), and I understand the nature of the processes that make up a carnot cycle - however I still can't make sense of it in my head. I've looked online and most people try and explain it...
  13. Hercuflea

    What Does 87% Efficiency Mean for an 80 Plus Gold PSU Rated at 1000W?

    Hi, When the modern 80 plus power supplies are quoted as being "87% efficient" on 100% load, does this mean that an 80 plus Gold PSU rated at for example 1000 Watts will provide 1000 Watts to the internal PC components, and therefore draw 1000/(0.87) = 1149.43 W from the wall? OR does it mean...
  14. L

    Limit on mechanical & electric energy conversion efficiency

    I regret to say that I know little of engineering, but, to make a long story short, I'm nagged by two questions about energy conversion efficiency. There is a thread i made titled "giant railguns recycling their own energy in space" in the science fiction & fantasy forum here that explains my...
  15. vetgirl1990

    Efficiency of a Carnot Engine

    The efficiency of a Carnot Engine is described by the relationship: Tc/Th = Qc/Qh, so that e(Carnot) = 1 - Tc/Th For heat engines, can their efficiency also be related to temperature as well? Or is the description of their efficiency just: e(heat engine) = W / Qh = 1 - Qc/Qh I am inclined to...
  16. T

    Electrical meter and efficiency question

    Q1. I know a DMM will anticipate a sineusoidal supply, thus there can be problems with spiky supplies. Even if you have a true RMS meter, it it's a spikey supply, non-sineusoidal, you still can't calculate the peak of a spiky supply? Does a DMM measure the peak, then calculate from THAT the...
  17. teslafanclub

    Energy efficiency Gain or Loss? What do you think?

    Energy efficiency related question: please help with an anwer to the following: Given a flat electrical coil of known dimentions, this coil is used as an induction coil, laid flat, on top of the cooking surface of an induction cooker. Basically, the induction cooker has a copper braided coil...
  18. ChrisVer

    Signal vs Bkg efficiency plots

    What information can one obtain from the plots of the background vs signal efficiency? \epsilon_{bkg}(\epsilon_{sig})? In particular I attach some plots I made by hand and I want to understand how to obtain what each tells us.
  19. M

    Understanding propulsive efficiency

    Hello, I've been trying to wrap my head around this topic and came across such a thread here: https://www.physicsforums.com/threads/propulsive-efficiency.643646/ but still don't get it. Why is it that that accelerating one unit of mass by two units less efficient than accelerating two units of...
  20. ryanuser

    Efficiency of piezoelectric materials

    I was told that "piezoelectric materials can become more efficient if they were made to reduce their elasticity (the ones such as PVDF films that are flexiable).This is because the external energy is used to force the film back to its original shape just like when a spring is squashed; so most...
  21. DavideGenoa

    Thermal efficiency: reversible and irreversible machines

    In the proof of Clausius inequality ##\oint\frac{\delta Q}{T}<0## for an irreversible cycle, I always find the fact that the thermal efficiency of an irreversible machine is **stricly less** than the thermal efficiency of a reversible machine, both operating between temperatures ##T_H## and...
  22. K

    B How to compare camera film ISO number to quantum efficiency?

    The efficiency of a scientific camera like http://www.princetoninstruments.com/products/imcam/proem/ is specified by the quantum efficiency vs wavelength. The meaning is simple enough. Assuming a fill factor of 1, it's the fraction of incident photons that generate a charge. But photographer...
  23. I

    Various ways of doing work to minimize entropy increase

    [Moderator's note: Recategorized thread to "Basic".] While driving alone through the beautiful scenery of Banff and Yoho national parks, a question formed in my mind. Which of these modes of slowing down a vehicle by an equal amount is likely to minimize the resulting overall increase in...
  24. Ryan_m_b

    Effect on efficiency when computing at lower energies

    Recently I've been in a discussion with someone online who claimed that the efficiency of a computer with regards to energy is not a linear relationship. I assumed that if you were to halve the power going into a computer chip (assuming it was designed to deal with that and wouldn't just turn...
  25. K

    Energy from food to Mechanical Energy & distance traveled

    Homework Statement An "energy bar" contains 22 g of carbohydrates. If the energy bar was his only fuel, how far could a 68 kg person walk at 5 km/h? Mass(person) = 68 kg; v = 5km/h; 22g carb = 4 Cal/1 carb = 88 Cal; P(power of man walking) = 380W (this is derived from my textbook). Homework...
  26. J

    Will a Faraday cage affect the efficiency of motors inside?

    "A Faraday cage or Faraday shield is an enclosure formed by conductive material or by a mesh of such material. Such an enclosure blocks external static and non-static electric fields by channeling electricity along and around, but not through, the mesh, providing constant voltage on all sides of...
  27. N

    Regarding efficiency of heat engines

    I tried to calculate the efficiency of a engine using the formula : Efficiency = (Net Work Done) / (Heat absorbed) And then I tried to calculate the efficiency of respective Carnot engine by two ways : 1) Efficiency = (Net Work Done) / (Heat absorbed) 2) Efficiency = 1 - (Temperature Lowest /...
  28. A

    How does a car's loads affect it's fuel consumption?

    Hi, so I was wondering about how the car's LED, MP3/IPOD, AC systems consumes up electrical power and then to fuel? Let's say that the loads are running for 5-7 hours. Thanks for the replies/ideas!
  29. Sai Kiran Aka

    How Is the Efficiency of a Generator Calculated?

    How to calculate the efficiency of a generator? Any formulas?
  30. Wazkey

    Self-studying vs Class lectures

    Which one do you think that is more efficient? I think that lecturers, from the fact of being humans, commit more mistakes than books when they give information because they can forget to transmit important details. Books are written carefully in order to be easy to understand, what's said was...
  31. I

    Amplitude modulation and amplifier efficiency

    " A intelligence signal is amplified by a 80% efficient amplifier before being combined with a 12kW carrier to generate the AM signal. if it is desired to operate at 100% modulation, what is the DC input power at the modulator" The choices are a: 12kW b. 7.14kW c.7.5kW d. 15kW my solution...
  32. C

    Increasing Compressor Efficiency Question

    I reference this forum all the time and you guys are always good at breaking down confusing questions so I decided I needed to make an account and get some help with a mental struggle I have been having for quite some time! Two commonly discussed ways of improving a compressor's efficiency in a...
  33. D

    Airflow and hair dryer efficiency

    Homework Statement Can the power efficiency of the domestic hair dryer be improved by reducing the heat energy and increasing airflow? Homework EquationsThe Attempt at a Solution
  34. E

    Efficiency calculation for solar cells

    Homework Statement Hi! I have a problem with the following problem: Calculate the efficiency of the solar cells with the characteristics given in the table below Power (28 degrees, BOL): 300 W/m2 Absorptance: <91 , emittance: >82. Reliability: 0.999 . Mass: 2 kg Homework Equations I know...
  35. A

    Ans: Calculate Annual Savings with 93% Efficient Motors for AHU Fans, Pumps & CT

    (b) An energy audit was conducted on a building to demonstrate energy savings opportunities by replacing the air handling unit or AHU fans motors, condensing and chilled water pump motors of the water cooled chilled water air-conditioning installation with newer, more efficient motors of the...
  36. J

    Efficiency of CNOT Gates in Quantum Circuit Design

    I'm constructing a quantum circuit that implements a gray code that connects the binary strings |0001> and |1110> using CNOT gates. Since the two strings are negations of each other, two equivalent circuits can be designed where the control qubit conditions are negated. My question is what is...
  37. C

    Heat Exchange and Efficiency in a Fridge

    Homework Statement In a 30% efficient, -16°C fridge, how much electrical energy will be used up to lower the temperature of 250 mL of 75°C water? If the fridge is rated at 150 W, how long will this process take? Specific Heat Capacity of Water = 4200 J/Kg×K Specific Heat Capacity of Ice = 2000...
  38. Aceix

    Is Electric Cell Efficiency Always 50% in Closed Circuits?

    Is the efficiency of a cell in a closed circuit always 50%?
  39. brianeyes88677

    The efficiency of a Carnot engine

    I can't realize the proving why Carnot engine has the highest efficiency. "Let εc be the efficiency of a Carnot engine operating between two given temperatures.If an engine X, which has an efficiency εx that is greater than εc.We can couple engine X to a Carnot refrigerator , and they make a...
  40. I

    Carnot cycle work & efficiency

    Homework Statement The oxygen contained in a thermally insulated container will be cooled down to its boiling point (-183 C), and then condensed. Thereby one uses a reverse Carnot process operating between the oxygen gas (instantaneous) temperature and the room temperature (17 C). What is the...
  41. A

    Water electricity pump, given efficiency percentage?

    Changing the potential energy of water is frequently used as a means of storing excess renewable energy when it is not needed and using it when it is needed. An electrically-powered pump with efficiency 62 % raises a 10 kg mass of water a height of 10 m. The water is subsequently allowed to...
  42. supak111

    Spin mass in a vacuum, efficiency?

    Hey guys I was wondering what would happen if: took a ball neo magnet, balanced it on a few other magnets to basically make it a frictionless bearing. Then spin the ball magnet to 10k rpm. But do all this in a box that's a vacuum. Would the neo ball magnet spin basically for a VERY long...
  43. M

    Thermal efficiency of a heat engine

    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 capacities...
  44. mattyboson12

    Steam Plant Cycle Performance: Analyzing Efficiency

    I am doing an experiment to determine the performance of a steam plant cycle and analyse it in comparison with the ideal rankine cycle. I have a sketch of the actual and real T-S diagram for the steam plant (See attached) I am unsure what factors cause the change in the shape of the T-S...
  45. M

    Energy project for Universities implementation

    Hello all, this is my first time posting here so please excuse if this maybe isn't the appropriate thread to post this in but I figured it may be the most relevant. I am working on writing a proposal (small, just 450 words), that aims to address the energy efficiency of a university, ie...
  46. CivilSigma

    Efficiency Calculation for a Stirling Engine Cycle

    Homework Statement Figure 2 represents a model for the thermodynamic cycle of the Stirling engine, patented by Scottish clergyman Robert Stirling in 1816. The engine operates by burning fuel externally to warm one of its two cylinders. A xed quantity of inert gas moves cyclically between the...
  47. A

    Why the Carnot Cycle? | Understanding Efficiency in Heat Engines

    1-Is the efficiency of heat engines working in cycles other than Carnot independent of the nature of substance used? Can we still claim that maximum efficiency in converting heat to work is attained during reversible processes for such cycles? For which engines/cycles can we do this? 2- Why is...
  48. P

    Internal combustion engine efficiency

    hello we know that there is 42% limitation in the efficiency of internal combustion engine, thermodynamically calculated by Carnot and we can never overcome this can someone explain me in few simple words why this is true? also, does this apply to the energy from internal combustion to...
  49. David Carroll

    How to calculate efficiency of Newton's Method

    Greetings. I was wondering if anyone knew of a way to calculate the efficiency of Newton's Method for a given function: I have an equation f(x) and I'm trying to find a value of x = x0 such that f(x0) = 0. So I start with a guess x0 and then use that to find a second (usually closer) guess...
  50. A

    Why are larger transformers more efficient than smaller ones?

    Homework Statement Transformer efficiency loss Homework Equations Larger transformers are more efficient than smaller The Attempt at a Solution I understand the basics of energy loss through heat etc but i don't understand why it would be different for the sizes of transformers. Is it to do...
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