Power: P = V × I

Your charger says 5 V, 2 A. How many WATTS? ⚡🔥

1️⃣ P = V × I: power = volts × amps. 5 V × 2 A = 10 W. Picture it as an AREA: a rectangle 5 tall and 2 wide holds 10 one-watt squares. Fast charging at 9 V × 2 A = 18 W.

2️⃣ A RESISTOR TURNS IT ALL INTO HEAT: 10 V across a 100 Ω resistor → I = V ÷ R = 10 ÷ 100 = 0.1 A → P = 10 × 0.1 = 1 W of heat. A normal ¼ W (0.25 W) resistor would cook and smoke! Pick a 2 W one.

3️⃣ SAME WATT, TWO MORE WAYS: P = I² × R = 0.1² × 100 = 1 W and P = V² ÷ R = 10² ÷ 100 = 1 W. Use the one that fits what you know.

📌 Rule of thumb: pick a resistor rated for at least DOUBLE the heat it will make.