A square threaded screw is used to lift a load $W$ by applying a force $F$. Efficiency of square threaded screw is expressed as
- The ratio of work done by $W$ per revolution to work done by $F$ per revolution
- $\frac{W}{F}$
- $\frac{F}{W}$
- The ratio of work done by $F$ per revolution to work done by $W$ per revolution