Explanation: The formula P = I²R is derived from the fundamental power equation P = IE (Power equals Current times Voltage) and Ohm's Law, E = IR (Voltage equals Current times Resistance). When we know current (I) and resistance (R), we can substitute E=IR into P=IE, which results in P = I(IR), simplifying to P = I²R. This formula is essential in amateur radio for calculating the power dissipated as heat in components like resistors, transmission lines, or amplifier stages, given a specific current flow and resistance. Understanding this relationship helps in selecting appropriately rated components to prevent overheating and failure. Option A, P = IE, is a correct power formula, but it requires knowing voltage (E), which the question does not specify as a known variable. Option C, PF = W/IE, is not a standard formula for power in a DC circuit; "PF" typically refers to power factor, a concept primarily relevant in AC circuits.