The efficiency of a screw jack is maximum, when (where $$\alpha $$ = Helix angle and $$\varphi $$ = Angle of friction)
A. $$\alpha = {45^ \circ } + \frac{\varphi }{2}$$
B. $$\alpha = {45^ \circ } - \frac{\varphi }{2}$$
C. $$\alpha = {90^ \circ } + \varphi $$
D. $$\alpha = {90^ \circ } - \varphi $$
Answer: Option B

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