Question

The thermal efficiency of an air-standard Brayton cycle in terms of pressure ratio r_p and $\gamma$ (=C_p/C_v) is given by              

      (a) $1-\frac{1}{r^{r-1}_{p}}$                                                           (b) $1-\frac{1}{r_{p}}$ 

      (c) $1-\frac{1}{r^{1/\gamma }_{p}}$                                                          (d) $1-\frac{1}{\frac{\left ( \gamma -1 \right )}{r_{p}^{\gamma }}}$