What is the meaning of useful flux?

What is the meaning of useful flux? Correct Answer the flux which can produce the output

Total flux is the maximum amount of flux that is being generated by the current flowing in the circuit. Useful flux is nothing but the flux which can produce the output in the machine.

Related Questions

What is the relationship between flux in the pole body and the useful flux per pole?
Heat flux increases with temperature drop beyond the Leiden frost point in the plot of heat flux vs. temperature drop for a boiling liquid, because