Maximum diagram efficiency for Parson’s reaction turbine is given by

A

$$\frac{2 \cos^2 \alpha}{(1 + \cos \alpha)}$$

B

$$\frac{\cos^2 \alpha}{(1 + 2 \cos \alpha)}$$

C

$$\frac{\cos^2 \alpha}{(1 + 2 \cos^2 \alpha)}$$

D

$$\frac{2 \cos^2 \alpha}{(1 + 2 \cos^2 \alpha)}$$