Explanation: In a DC circuit, electrical power (P) is defined as the rate at which electrical energy is transferred. The fundamental formula for calculating power when voltage (E, also often denoted as V) and current (I) are known is a direct application of Watt's Law. Option A, **P = EI**, correctly represents this relationship. Power, measured in watts, is equal to the voltage (in volts) multiplied by the current (in amperes). This formula is foundational for understanding power in direct current circuits. Option B, P = (I squared) R, is also a valid formula for power, derived from P=EI by substituting Ohm's Law (E=IR). However, it requires knowing the resistance (R), which the question specifically states is *not* known, only current and voltage. Therefore, while true, it's not the direct answer to the given conditions. Option C, PF = W/IE, contains "PF" which typically refers to Power Factor, a concept exclusively used in AC circuits, not DC. The formula itself is also nonsensical for calculating power in a DC circuit. Therefore, P = EI is the precise formula to use when current and voltage are the known variables in a DC circuit.