Question T5C08
From subelement T5 - T5C
What is the formula used to calculate electrical power (P) in a DC circuit?
Why is this correct?
Power equals current times voltage: P = I × E (option A). Power is the rate of energy consumption, measured in watts. The other options are incorrect because dividing voltage by current (B) gives resistance, while subtracting (C) or adding (D) voltage and current produces meaningless values with no physical significance in electrical circuits.
Memory tip
Remember 'PIE' - Power equals I times E. This multiplication relationship makes intuitive sense: more current OR more voltage means more power consumption. Division, addition, and subtraction don't represent the multiplicative nature of how electrical energy is actually consumed in circuits.
Learn more
In practical amateur radio operation, this formula determines your transmitter's power consumption from your power supply. A 100-watt transceiver drawing 8 amperes from a 13.8-volt supply confirms P = I × E (8A × 13.8V ≈ 110W, accounting for inefficiency). Understanding power calculations helps you properly size power supplies, select appropriate fuses, and calculate battery life for portable operations.
Think about it
Why do you think power is calculated by multiplying current and voltage rather than adding them together?