Efficiency Definition and 901 Threads

This is a very quick question but in the equation e=1-Q_{C}/Q_{H} do we treat both Q's as positive even though heat goes in in one case and out in the other? Or is there some detail I'm missing that would otherwise make the result less than 1.

I'm trying to reproduce the plot in the attached figure. I know the band-gap energies, so I was hoping there was some simple way I could get the quantum efficiency as a function of wavelength. I read on wiki that Energy(eV) = 1240/wavelength(nm), so I mechanically plugged those in, and got...

Homework Statement A Student Performs an experiment in which an electric motor is used to lift a 200g weight through 2m, thus increasing its potential energy by 4j. From measurements of the rate at which the weight is lifted the efficiency of the motor is to be determined. Two different...

The theoretical maximum efficiency of silicon solar cells is about 29%. How is this theoretical maximum efficiency derived? How can I use the working principles of a silicon solar cell to explain this?

for a given volume of gas,is it more efficient to compress smaller volumes of gas more no. of times or compress large volumes of gas less no. of times?

I'm observing the circular process of a heat engine. It's p-v diagram is So between points 3 and 4 the heat is extracted. That causes losses since the efficiency if given by \eta =1- \frac {Q_c} {Q_h} Where Qh is the heat the heat source has given and Q_c the amount of heat that...

Homework Statement The specifications of a transformer for a small appliance read "Input: 110 V, 6.4 W" and "Output: 8.9 V, 270 mA". What is the efficiency of this transformer? Homework Equations P = I * V V = I * R The Attempt at a Solution 6.4 W / (8.9*(270*.001)) ---> I think this is...

Homework Statement http://img291.imageshack.us/img291/7786/effx.jpg Homework Equations e=1-1/(V1/V2)^(gamma-1) The Attempt at a Solution This is a practice test where he gives the solutions, as you can see the first thing he asks for is the efficiency, and lists the answer as...

Efficiency of Ejector "as pump" I was asked to find the efficiency of a steam ejector experiment "as a pump". So I tried the formula : [(m(P/density + V^2/2))discharge - (m(P/density + V^2/2))suction]/ (m(P/density + V^2/2))steam inlet. I am getting an efficiency of 0.5%. Is this a...

Hi all, Got a bit of a problem with a lab experiment at uni (I'm not sure if this is the right place to post this, mods feel free to move it if necessary!) Anyway: We're trying to get a plot of efficiency against energy for a planar germanium detector. We've got spectra for different...

Homework Statement On a hot day a house is kept cool by an air conditioner. The outside temperature is 32°C and the inside temperature is 21°C. Heat leaks into the house at the rate of 9000 kcal/h. If the air conditioner has the efficiency of a Carnot engine, what is the mechanical power that...

The medieval trebuchet is a missile-throwing device, with a heavy counterweight on the short end of a beam that pivots about an axle fixed to a supporting frame. A sling is attached to the long end, and when properly "tuned" by adjusting its length, it will release the missile at exactly the...

A question regarding power supply efficiency: The theoretical maximum efficiency of a full-wave rectifier circuit with a resistive load and no smoothing is around 82%. In the calculations to derive that the resistance of the source or the rectifiers does not enter into the equation, so the...

I am currently in the process of writing a program in VBA that will numerically "solve" a given n-body gravitational problem. I'm doing this pretty much just for fun and am by no means a programmer (had a 1 semester course in c++). The question I have is something that seems to keep coming into...

Homework Statement Well, this isn't really a number question, but I'm wondering if the larger the k of a spring, if that will make the energy transformation of a weight from potential energy to spring energy more efficient? Homework Equations F=-kx ; energy before = energy after The...

Hi, I would like help to solve the following question. Q: The graph shows the fuel consumption c of a car (measured in gallons per hour) as a function of the speed v of the car. At very low speeds the engine runs inefficiently, so initially c decreases as the speed increases. but at high...

hii frends, im a doing a project on the efficiency improvement of a velocity compounded impulse steam turbine. we plan 2 do that by varying the input mass flow rate of steam and finding out the particular mass flow rate at which maximum efficiency is attained. the data i could collect...

Homework Statement What could you do to increase efficiency between the cart and the ramp? As in pulling a cart (with wheels) up an inclined plane. Homework Equations The Attempt at a Solution One solution could be increasing the angle to increase efficiency. I was wondering...

Does a 60W Type A (general service) incandescent light bulb put out more light than a 60W Type B (candelabra torpedo) incandescent light bulb?

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.

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...

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...

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...

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...

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} =...

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...

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...

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...

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...

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...

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...

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

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...

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...

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...

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...

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)

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...

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.

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...

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...

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...

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)?

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...

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...

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...

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...

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.

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...

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...