Download Parallel Circuits

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. 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.
