Find the efficiency of a cycle consisting of two isochoric and two isothermal lines if the volume varies `v-fold` and the absolute temperature `tau-fold` within the cycle. The working substance is an ideal gas with the adiabatic exponent `gamma`.

Explanation

We have
`Q'_1 = tau RT_0 1n v, Q''_2 = C_V T_0 (tau -1)Q_1 = Q'_1 +Q''_1` and
`Q'''_2 = RT_0 1n v, Q''_1 = C_V T_0 (tau -1)`
as well as `Q_1 = Q'_1 + Q_1''` and
`Q_2' = Q_2'' + Q_2'''`
So `eta = 1-(Q'_2)/(Q_1) +1 =(C_V(tau -1)+R 1n v)/(C_V (tau -1)+ tau R 1n v)`
=`((tau - 1)/(gamma -1) + 1n v)/((tau - 1)/(gamma_1) + tau 1n v) = ((tau -1) 1n v)/(tau 1n v + (tau -1)/(gamma-1))`.
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