Lesson 9 Parallel Circuits

Last class review A series circuit is useful when you want to control many devices with a single switch. We also learned that if multiple loads are connected in series the current across the load drops and if multiple sources are connected in series the voltage across the load increases.

parallel circuit When you want devices to work on their own, you need a different kind of circuit. You need a circuit that has more than one pathway for electric current. This kind of circuit is called a parallel circuit.

parallel circuit Think of a parallel circuit as being like a set of roads. Cars can follow different routes to return to the starting point. If one road is blocked, cars can still move along the other roads. In the same way, if one branch of a parallel circuit is opened, current still flows though other branches of the circuit.

Look at the diagram to the right Look at the diagram to the right. If you open the switch, how many bulbs will stay lit? Two

Use the correct symbols to draw a diagram of a parallel circuit that has one battery, and three bulbs connected in parallel.

How many complete pathways are there for electric current to flow in this circuit? There are three pathways

Adding Loads in Parallel When loads are added in parallel, the current through the load stays the same. However, the total current in the circuit increases.   If sources are connected in parallel, the voltage across each load stays the same. However, each source contributes less energy to the circuit which allows it to last longer.

Lab Lab: Current in a Parallel Circuit You have seen what happens to the current in a circuit when you add loads in series (decreased). Do you think adding loads in parallel gives the same result? Design a way to find out.