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. J

    Thermal Efficiency of a Heat Engine based on pV-diagram

    Homework Statement Here's a link to the pV-diagram I am using - http://session.masteringphysics.com/problemAsset/1396784/2/p16.7.jpg A heat engine takes 2.0 moles of an ideal gas through the reversible cycle abca, on the pV diagram shown in the figure. The path bc is an isothermal process...
  2. K

    What is the Efficiency of the system?

    Question: An hand crank is used to life a bucket of water from a well. The bucket and water have a combined mass of 12.0 kg and must be raised 8.5 m. The force used to lift this load is 40.0 N and must be applied over a total circular distance of 15.0 m. What is the efficiency of the system...
  3. A

    Improving IC Engine Efficiency: Reducing Heat Loss Through Cylinder Walls

    hi.I would like to know something about the IC engine.I just read an article.It said that 30% efficiency is gone through conduction of heat by the cylinder wall.If it is reason for one of the efficiency loss why can't we build an cylinder coated with a material that is non conduction.So only...
  4. STEMucator

    Calculating Error in Efficiency of Half Wave Rectifier

    Homework Statement A single phase half wave rectifier produces a DC signal ##V_{DC} = (4.6 \pm 0.78) V## and AC signal ##V_{AC} = (0.22 \pm 0.036) V##. What is the error on the efficiency? Homework Equations Functional dependence, propagation of error: ##\sigma_f = \sqrt{...
  5. R

    Torque and volumetric efficiency relationship

    Hello Guys, From the torque curves of most of the ic engines it can be seen that torque is maximum at a particular rpm range then it starts dropping. It is said that the torque is maximum when the volumetric efficiency is maximum , i just can't understand the relationship between the both...
  6. D

    Is Gasification More Thermodynamically Efficient Than Direct Combustion?

    Hi there, I have been thinking about attempting to quantify the statement that: "Gasification is more efficient thermodynamically than direct combustion of the fuel source as the gas can be combusted at higher temperatures, resulting in higher thermodynamic efficiencies as defined by...
  7. D

    Motor Powering Generator Efficiency

    What do I look for to determine the efficiency factor to know how many watts I can get out of a generator given a specific known HP sized engine? Example: 12.6 HP gives 9395 Watts from the standard HP to Watts conversion... however on a Markon generator, the spec sheet says that a 12.6 HP...
  8. E

    Efficiency of Objects Pushed Up a Ramp

    Homework Statement Objects A (2.0 kg), B (1.0 kg), and C (1.0 kg) are pushed up a ramp, which is 4.0 m and 1.2 m high. The applied forces are parallel to the ramp with magnitudes of 9.8 N on A, 4.9 N on B, and 3.1 N on C. Homework Equations Eff = W(output) ÷ E(Input) x 100% W = F...
  9. D

    What is the best solar efficiency out there?

    I read there are transparent solar panels which are also flexible, Then I read carbon base solar panel. Then sun capture that concentrate to panels like other fresnel lens or dish like. Then there is this idea that people can print out their own flexible solar panels with photovoltaic ink...
  10. L

    Calculate Efficiency of Hill for Snowboarder

    Homework Statement A snowboarder goes down a ramp when initially at rest. The Total mechanical energy on top of the hill is 980 J and 400J at the bottom of the hill. Calculate efficiency of the ramp. Homework Equations Efficency = (Power out) over (Power in) The Attempt at a...
  11. A

    Improving Cooling Efficiency: Two Effective Strategies

    Discuss two measures that can improve the cooling efficiency.
  12. S

    Heat Engine efficiency Problem

    Please help me with the question below with a proper explanation and also suggest me a reference to read for the same. Thank you! A solar collector receiving solar radiation at the rate of 0.6 kW/m2 transforms it to the internal energy of a fluid at an overall efficiency of 50%. The fluid...
  13. W

    How is Efficiency of Heat Exchangers (HRV) determined

    I've be looking at the specs for Heat Recovery Ventilators (HRV). They commonly state that they can recover 85% of the heat. How is that possible? To me you could only every recover 50% in a perfect situation because of the equal volume of airflow's. Won't the air temperatures just stop at...
  14. L

    Find Bandwidth Efficiency (R/B) given SNR and Eb/N0

    Thank you in advance for your help!What is the bandwidth efficiency (R/B) of PSK for a bit error rate of 10^-7 on a channel with an S/N of 12 dB?[/b] From the graph, for BER= 10^-7, Eb/N0 = 11.2 dB./b]I have applied the formulae Eb/N0 = S/N * B/R Where, S/N is Signal power over noise power *...
  15. cavalierean

    Calculating Efficiency of a DC Motor: How Do I Determine In and Out Values?

    Hi I am trying to calculate the efficiency of my DC motor. I know that efficiency is: Power Out / Power In * 100 I have been told by my teacher that Power In is calculated by the following formula, Power In = Power * Time And Power Out is; Power Out = Mass * Gravity * Height...
  16. I

    Need advice on the efficiency of a particular study habit that I have.

    Hi, I'm not sure if this is the correct sub-forum to post this question, so I apologize in advance if this post is misplaced. Anyways, a little about my self: I'm a Junior in high school, My passion is in physics and mathematics and I plan to major in physics and preferably get a PHD in it...
  17. M

    Efficiency of Stirling heat engines

    Not sure if this should be posted in the general physics forums or in the hw/coursework section. I'm in my second semester of general physics and have to do a class project. For my project I built an alpha type Stirling engine. In the paper I need to write I need to explain how it works using...
  18. E

    Calculating Efficiency of an Engine with Moving Piston

    A question is being asked about a combustion chamber that has a moving piston; "an engine." "Which expression expresses the efficiency of the engine?" The answer given is: (Pressure(from burning))(Volume)/(moles)(delta H) While this looks some thing like PV = nRT, I don't fully understand...
  19. A

    Calculating Efficiency of a Solar Cell Indirectly

    Not sure if this is the right section for this, I apologize in advance. I have a project to do and my goal is to measure the efficiency of a solar cell INDIRECTLY. I am not sure how to do that. The equation for the efficiency of a solar cell is η = P/E*A. Where P is the cells...
  20. marellasunny

    Drivetrain efficiency is a function of what?(gear ratio,eng.speed )

    By the conservation of energy, P_in=P_out So,no matter what gear ratio 'i' I choose, P_out=P_in, since the gear ratio 'i' term would get canceled at the numerator and denominator. $$P_{eng}= ω_{eng} M_{eng}= i . ω_{out} \frac{M_{out}}{i}$$ hence P_in=P_out But, what is the drivetrain...
  21. M

    Alternator , generator efficiency

    Hi I've been looking in google although I can't find a definitive answer, what are the usual efficiency range for alternators, some talk about brushed ones in the range of 50 to 60 % , brushelss some say go as highas 75%, maybe some of you folks know from your experience what are the typical...
  22. A

    Is the efficiency of heat engine more in hilly areas than in plains?

    In hilly areas temp is low than plain areas.So the temperature of source as well as sink must be low.But ratio remains same.So efficiency is same as in plain areas? Is my logic correct? Or anything else? Can it be more?
  23. A

    Efficiency - how to get the maximum efficiency in a circuit?

    efficiency -- how to get the maximum efficiency in a circuit? Homework Statement I don't quite understand how to get the maximum efficiency in a circuit. Exemple. 4 Volts and 2.0Ω will produce 8 watts with a current of 2.0 amps. 5 Volts and 3.1Ω will produce 8 watts with a current of...
  24. T

    How Does Current Affect Li-Ion Battery Efficiency?

    Hi, I am trying to figure out how Li-Ion batteries operate in regards to efficiency. I understand they have rated voltage and current etc. and to operate them at these parameters if possible. However, I'm wondering is it simply the current that has effect on their efficiency. By Efficiency I...
  25. U

    Fin effectiveness vs fin efficiency for applications

    So we've been doing fins in class. I understand that the formulas for fin effectiveness and efficiency are similar, except the area used in the denominator (Ac i.e. area of cross-section for effectiveness and As i.e. surface area for efficiency). However, my question is while designing a...
  26. G

    Reversible Clapeyron cycle efficiency

    Homework Statement The Clapeyron cycle efficiency is similar to the Carnot cycle except that two adiabatic paths are replaced with isobaric processes a) based on the above information, draw a Clapeyron cycle. b)Derive the efficiency of the reversible Clapeyron cycle Homework...
  27. T

    Energy conversion efficiency (Light -> heat)

    Hi, all I'm seeking advice on how to calculate the energy conversion efficiency, in case of heat from light energy. I think that one of the general formulas 'energy output/energy input' can not be applied in this problem. Assuming that light(or laser) has 10W power output and material 1...
  28. S

    Isentropic efficiency vs polytropic efficiency of a gas turbine

    My classmates and I are working on a senior design project where we optimize a baseline turbofan for supersonic cruise. We are a little confused about when to use polytropic vs isentropic efficiencies. I have read to begin with isentropic, however is there anyone who could explain a little more...
  29. C

    Heat Efficiency of a Carnot Engine

    Homework Statement A Carnot engine operates between a warmer reservoir at a temperature T1 and a cooler reservoir at a temperature T2. It is found that increasing the temperature of the warmer reservoir by a factor of 2.00 while keeping the same temperature for the cooler reservoir increases...
  30. O

    Maximizing Car Efficiency: Utilizing Flywheels for Rotational Motion

    can we convert the linear motion into rotational motion in cars using a fly wheel under the car ?
  31. E

    Piezoelectric transformer efficiency

    Dear all, How is the efficiency of piezoelectric transformer higher than electromechanical coupling factor? Thank you, Husain
  32. B

    Carnot efficiency vs thermal efficiency

    Is Carnot efficiency the same as thermal efficiency?
  33. anubodh

    Can Regenerative Brakes Improve Efficiency on Non-Electric Vehicles?

    Is regenerative brake technology available on vehicles other than ecars and ebikes.if so what is the maximum efficiency reached till now on bikes and cars.
  34. P

    How to improve the efficiency of a propeller?

    Homework Statement One of your friends is building his own airplane. He has received a quotation for a two-bladed propeller with an efficiency of ##\eta = 80\%## . He asks for your advice on whether it is possible to get a higher efficiency - what is your answer? no, the efficiency based on...
  35. E

    How Do You Calculate Thermal Efficiency in a Diatomic Gas Heat Engine Cycle?

    Homework Statement You build a heat engine that takes 1.00 mol of an ideal diatomic gas through the cycle abc, where segment bc is isobaric and segment ca is isochoric. calculate the thermal efficiency of the engine. this is a 5 part problem and I already solved for Wo and Wo=Qo I solved...
  36. B

    Heat engines and finding efficiency

    Hello, Homework Statement Engine A receives four times more input heat, produces six times more work, and rejects three times more heat than engine B. Find the efficiency of (a) engine A and (b) engine B. Homework Equations e = |W|/|QH| e = 1 - |Qc|/|QH| The Attempt at a...
  37. P

    Solve Efficiency Problem: Heat Water in 1000 W Electric Kettle

    Homework Statement Determine the amount of time it will take a 1000 W electric kettle to heat up 1.0 L of water to boiling point if the water starts at 10 °C and the kettle is made from 400 g of iron. The transfer of heat energy from the kettle to the water is 63%.Homework Equations P = W/Δt Q...
  38. W

    How would you quantify and predict the efficiency of a bungee cord?

    I am in an introductory physics class and we have been working with Gravitational Potential Energy, Elastic Potential Energy, Kinetic Energy and the Law of Conservation of Energy in relation to bungee cords. Recently, we delved into the topic of efficiency and with it I came upon the following...
  39. MacLaddy

    Thermal Efficiency in an Ideal Diesel cycle.

    Homework Statement Helium in an ideal Diesel cycle is compressed from 4 L to 0.25 L, and then it expands during the constant pressure heat addition process to 0.50 L. Under air standard conditions, the thermal efficiency of this cycle is: a) 79.5% b) 20.5% c) 61.4% d) 67.4% e) 84.3%...
  40. rkum99

    Improving vacuum system efficiency?

    So I was looking through the internet on how one could improve the efficiency of a vacuum system (with a diffusion pump). Lots of websites describe systems with, cold traps to remove condensable vapors such as water. If I am not mistaken, cold traps also help prevent back streaming, similar...
  41. T

    Can the Span Efficiency Factor Exceed 1 in the Lifting-Line Theory?

    Hello Everybody, Span efficiency factor appears in the lifting-line theory of Prandtl describing Lift and vortex drag of a finite wing. According to this theory, the most efficient wing is an elliptical one and, roughly speaking, the span efficiency factor defines an efficiency of a given wing...
  42. T

    Can albatrosses fly without using updrafts?

    Hello Everybody, Span efficiency factor appears in the lifting-line theory of Prandtl describing Lift and vortex drag of a finite wing. According to this theory, the most efficient wing is an elliptical one and, roughly speaking, the span efficiency factor defines an efficiency of a given...
  43. T

    Thermodynamics Efficiency Of Adiabatic Compressor

    1. 100kg of methane is compressed from 0.5MPa and 300K to 3.0Mpa and 500K in a closed chamber by a compressor. The compression process is assumed to be adiabatic, calculate the efficiency of this compressor. Specific heat capacity of methane under constant pressure is 35.58 kJ/k.mol.K and ideal...
  44. K

    Would wind tubine on moving automobile pomote inlet efficiency?

    Question as the title above ! Could we use the wind turbine to compress the air into engine cylinder as the exhaust compression tubine does ? Thanks all for replying !
  45. O

    How Much Waste Thermal Energy Does a 5% Efficient 100W Bulb Produce in an Hour?

    Homework Statement An incandescent bulb is only 5.0% efficient. How much waste thermal energy is porudced by a 100.0W bulb in 1.0h? (Anwer=95J)Homework Equations P = E/T Efficiency = Eout/Ein x 100%The Attempt at a Solution P = E/T E = PT...
  46. H

    Another Energy Efficiency Equation Problem

    Homework Statement A golf club with 65 J of kinetic energy strikes a stationary golf ball with a mass of 46 g. The energy transfer is only 20% efficient. Calculate the initial speed of the golf ball. Homework Equations efficiency = E out/E in x 100% The Attempt at a Solution I...
  47. C

    Waste power plant efficiency math problem

    Homework Statement If 230 million tonnes of solid waste were burned in waste-to-energy power plants that are 20% efficient a) how many kilowatt- hours of electrical energy could be produced in a year? Compare this quantity with the total US electrical energy production of 3.8 trillion...
  48. H

    Energy Efficiency: Input & Output (Work/Energy)

    Homework Statement In a race, a 54 kg athlete runs from rest to a speed of 11m/s on a flat surface. The athlete's body has an efficiency of 85% during the run. How much input energy did the athlete provide? Homework Equations efficiency = E out/E in x 100% The Attempt at a Solution...
  49. S

    Engine thermal efficiency and Volume ratios

    The question: A perfect gas undergoes the following cyclic processes: State 1 to 2 cooling at constant pressure. State 2 to 3 heating at constant volume. State 3 to 1 adiabatic expansion. Deduce an expression for the thermal efficiency of the cycle in terms of r the...
  50. A

    Calculation actual efficiency problem

    Homework Statement A heat engine takes in 1030 J of energy at 1000 K and exhausts 585 J at 250 K. What are the actual and maximum theoretical efficiencies of this heat engine? Homework Equations For maximum efficiency I got 75 % by taking 1 - (250K / 1000K). For actual efficiency the...
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