Current in a parallel circuit

What is a parallel circuit?

In a parallel circuit, the current splits into several branches from a node and then rejoins further along. Each branch may contain a different load (a lamp, for example).

The node rule

At a node, the current flowing in is equal to the sum of the currents flowing out. For two parallel branches, this gives:

I = I1 + I2

where I is the current in the main circuit (before or after the branch), and I1 and I2 are the currents in each branch.

Practical example

A generator supplies two lamps, L1 and L2, connected in parallel:

Branch	Current
Branch 1 (L1)	I1 = 0.20 A
Branch 2 (L2)	I2 = 0.15 A
Main circuit	I = I1 + I2 = 0.35 A

The total current supplied by the generator (0.35 A) is distributed between the two branches according to the loads they contain.

Pitfall to avoid

Do not confuse the law for a series circuit (where I is the same everywhere) with that for a parallel circuit (where I is distributed between the branches). Always check, on a circuit diagram, whether the loads are on the same loop (series) or on different branches (parallel) before applying a rule.