If $$V_i$$be the inlet absolute velocity to blades, $$V_b$$ be the tangential blade velocity and $$\alpha$$ br the nozzle angle, then for maximum blade efficiency for single-stage impulse turbine

A

$$\frac{V_b}{V_i} = \cos \alpha$$

B

$$\frac{V_b}{V_i} = \frac{\cos \alpha}{2}$$

C

$$\frac{V_b}{V_i} = \cos^2 \alpha$$

D

$$\frac{V_b}{V_i} = \frac{\cos^2 \alpha}{2}$$