In a parallel circuit, the total resistance is calculated by using the formula 1/RT = 1/R1 + 1/R2 + 1/R3 + ..., where RT is the total resistance and R1, R2, R3, etc. are the individual resistances of the components in the circuit.
In a series circuit, the total resistance is calculated by simply adding up all the individual resistances of the components in the circuit.
In a parallel circuit, the total current is equal to the sum of the individual branch currents. This can be calculated by using the formula IT = I1 + I2 + I3 + ..., where IT is the total current and I1, I2, I3, etc. are the individual branch currents.
In a series circuit, the total current is the same throughout the circuit and can be calculated by using Ohm's Law, where IT = V/R, with V being the voltage and R being the total resistance of the circuit.
The direction of current flow in a circuit is determined by the direction of the voltage source. Current flows from the positive terminal of the voltage source to the negative terminal in a closed circuit.