The efficiency of a screw jack is maximum when

(a) \(\alpha=\frac{\pi}{4}-\frac{\phi}{2}\)

(b) \(\alpha=\frac{\pi}{4}+\frac{\phi}{2}\)

(c) \(\frac{\pi}{2}-\frac{\phi}{2}\)

(d) \(\frac{\pi}{2}+\frac{\phi}{2}\)