What is a situation where the efficiency of a device would change based on a redefinition of what is considered useful energy?[/B]
What would be considered useful energy?
How can the efficiency of a device change?[/B]
The Attempt at a Solution
If heat or sound can be considered as useful energy, the overall percentage of efficiency would improve. For example, the heat of light bulbs could provide warmth as well as light.[/B]