How is the efficiency of an electrical system calculated?

The efficiency of an electrical system is calculated by determining the ratio of useful output power to the total input power, expressed as a percentage. This formula, Efficiency = (Output Power / Input Power) × 100%, is fundamental in assessing how effectively the electrical system converts input energy into useful work.

In practical terms, if a system outputs 80 watts of power while consuming 100 watts, the efficiency would be calculated as (80 / 100) × 100% = 80%. This highlights both the effectiveness of the system and any losses incurred, such as those from heat, resistance, or other inefficiencies.

The other options do not accurately reflect the standard calculation for efficiency in electrical systems. For instance, subtracting input power from output power does not provide a meaningful efficiency metric, as it ignores the context of input versus output in relation to percentage performance. Similarly, comparing currents or voltages without consideration of power fails to provide a direct measurement of the system's overall efficiency.