Electric Power in a Circuit?

📌 CONCEPT: Electric power is the rate at which electric energy is transferred by an electric circuit. It is measured in watts (W) and is calculated as the product of the voltage and current in the circuit.

📐 RULE / FORMULA: The formula to calculate electric power is P = VI, where P is the power in watts, V is the voltage in volts, and I is the current in amperes.

💡 WORKED EXAMPLE: Given a circuit with a 10 V battery and a 500 Ω resistor, if the current flowing through the circuit is 0.1 A, the external power dissipated in the resistor can be calculated as P = (10 V) × (0.1 A) = 1 W. Additionally, the internal resistance of the battery is 5 Ω. To find the total power dissipated across the circuit terminals, we also need to consider the power lost in the internal resistance, P_internal = (0.1 A)² × (5 Ω) = 0.005 W. Therefore, the total power dissipated is P_total = P + P_internal = 1 W + 0.005 W = 1.005 W.

⚠️ COMMON MISTAKE: Students often forget to consider the internal resistance of the battery when calculating the total power dissipated in the circuit.