Question

Define the efficiency of a machine. Why the efficiency of the practical machines is less than 1?

Answer 1

1. The efficiency of a machine is defined as the ratio of work output to the work input.
2. The work done on the machine by applying the effort is called work input. Similarly, the work done by the machine on the load is called work output.
3. Now from the definition,

$Efficiency,\mathit{\eta }=\frac{Workoutput}{Workinput}$

4. Sometimes efficiency of a machine is given in percentage as,

$Efficiency,\mathit{\eta }=\frac{Workoutput}{Workinput}\times 100\%$.

5. Efficiency has no units. The efficiency of an ideal machine is 1 (or 100%) mechanical advantage is numerically equal to the velocity ratio.

6. However, due to friction between the moving parts of the machine, the efficiency of the machine is less than 1.