In the Circuits Gizmo, you learned how to use Ohm’s law: I = V/R, to determine the current in parallel and series circuits. But how do you find the resistance and current in a complex circuit that has both series and parallel elements? First, review how to find the equivalent resistance of a parallel circuit Use the Advanced Circuits Gizmo to construct the parallel circuit shown at right, using a 10-ohm and a 20-ohm resistor. Set the Selected battery voltage to 20 volts. Move the Ammeter next to the battery. What is the current? Based on Ohm’s law, what is the equivalent resistance in the circuit? You can calculate the equivalent resistance of a parallel circuit using the following equation: