Definition of crushing efficiency: choose the correct ratio expressing crushing efficiency.

Introduction / Context:
Efficiency metrics compare useful output to input energy. In comminution (crushing/grinding), only a tiny fraction of the input energy actually creates new surface area (useful work). Most is dissipated as heat, elastic/plastic deformation, and noise. Understanding this definition highlights why comminution is energy-intensive.

Given Data / Assumptions:

• Useful work in crushing = surface energy associated with new surfaces created.
• Input energy = energy supplied to the machine (or absorbed by it).
• We ignore minor differences between motor input and energy delivered to breakage zone.

Concept / Approach:
Crushing efficiency η is defined as η = (Surface energy created) / (Energy supplied). Because the surface energy increment is small relative to total power draw, η is typically very low (well under 1%). This underscores the importance of choosing appropriate machines and operating conditions to minimise energy waste.

Step-by-Step Solution:
Identify the 'useful output': creation of new surface area.Identify the 'input': energy supplied to the machine.Form the ratio: η = Surface energy / Supplied energy.

Verification / Alternative check:
Classical texts contrast Rittinger's, Kick's, and Bond's laws for energy–size relationships; all imply low overall efficiencies in practical crushing operations.

Why Other Options Are Wrong:
They invert the ratio or substitute non-standard definitions that do not reflect the efficiency concept.

Common Pitfalls:
Confusing 'energy absorbed by the solid' with 'energy supplied to the machine'; losses occur between the two, but the standard efficiency reference uses supplied energy.

Final Answer:
Surface energy created by crushing / Energy supplied to the machine