What is the engine's thermal efficiency?

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SUMMARY

The thermal efficiency of a heat engine using 110g of helium is determined using the formula n=W/Q_h. The user calculated work (W) as 0.008J based on the area of a triangle, but this approach is incorrect. Instead, the work should be calculated by integrating dW = P*dV, where P is defined by the ideal gas law P=nRT/V. The user incorrectly assumed Q_h to be 2200K, which should represent the heat input rather than a temperature.

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Homework Statement



A heat engine using 110g of helium as the working substance follows the cycle shown in the figure.

http://session.masteringphysics.com/problemAsset/1074114/5/19.P59.jpg

What is the engine's thermal efficiency?

Homework Equations



n=W/Q_h

The Attempt at a Solution



Alright so up to this point I have figured out p1,p2,p3, T1,T2,T3, V1,V2, and V3.

I tried doing W = area of triangle = .5(5-1)atm*(5.0*10^-3-1.0*10^-3)m^3 and got .008J. I assumed Q_h was 2200K because that is what I got for the temperature between T2 and T3, and that is where the heat should be going in. So I divided and 36.36% but that is wrong. Any help here? Thanks!
 
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Work is not a triangle in this case. You'll have to integrate dW = P*dV, where P = nRT/V.

Also, why is Q_h a temperature of 2200 K and not a heat transfering into the engine cycle?

Heat units = Joules

Temperature units = Kelvin
 

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