Which of the following best defines energy efficiency in electrical systems?

Energy efficiency in electrical systems is best defined as the comparison of energy input to useful energy output. This definition highlights the effectiveness of a system in converting the energy it receives into useful work or output, while taking into account the energy that is lost or wasted in the process.

In this context, a highly energy-efficient system would have a high ratio of useful output to input energy, meaning that a larger portion of the energy used is effectively employed for the intended purpose rather than being dissipated as heat, vibrations, or other forms of energy loss. This understanding is crucial for optimizing energy consumption and reducing waste, which are key goals in modern electrical systems.

The other definitions presented do not encapsulate the concept of efficiency in the same way. For example, the ratio of input energy to wasted energy focuses only on losses and does not consider the useful output as part of the efficiency evaluation. Similarly, the conversion of electrical energy to thermal energy does not necessarily reflect how efficiently a device operates; rather, it describes a specific transformation of energy that may or may not be beneficial. Finally, the total energy consumed by a device does not provide any insight into the effectiveness of that energy usage in producing useful work, thus falling short of defining energy efficiency.