Electrical resistance converter

Ohm's law ties the three together: voltage = current × resistance (V = I·R), and power = voltage × current (P = V·I). Mains supply is 230 V in Europe and 120 V in the Americas, a phone charger delivers 5 V at up to 3 A, a car battery 12 V, and an AA cell 1.5 V. A 2,000 W kettle on 230 V draws 8.7 A, which is why a 10 A or 16 A circuit breaker is on the line; a lightning stroke carries about 30 kA, an LED needs 20 mA.