1. Electric Circuits
Ch 17, section 4

2. Parts of an Electric Circuit
An electric circuit is a complete, closed path through which electric charges flow.
All circuits need 3 basic parts:
Energy source
Wire
Load
Loads change electrical energy into other forms of energy. As loads change electrical energy into other forms, they offer some resistance to electrical currents.

3. A Switch to Control a Circuit
A switch is used to open and close a circuit.
For charges to flow through a circuit, the switch must be closed or turned on.
If a switch is open or turned off, the loop of the circuit is broken so charges cannot flow through it.

4. Types of Circuits
The loads in a circuit can be connected in different ways, which results in two types of circuits:
Series Circuit
Parallel Circuit
The main difference between these circuits is the way the loads are connected to one another.

5. Series Circuit
A series circuit is a circuit in which all parts are connected in a single loop.
There is only one path for the charges to follow, so the charges moving through a series circuit must flow through each part of the circuit.
Ex: some strings of holiday lights
The current in a series circuit is the same through every device connected on the circuit. Adding resistors to a series circuit decreases the current in the circuit by increasing the total resistance.
Use for Series Circuits
Series circuits are good for burglar alarms because when the circuit it is broken, the alarm sounds.

6. Uses for Parallel Circuits Most buildings use parallel circuits.
A parallel circuit is a circuit in which loads are connected side by side.
A parallel circuit is a circuit that has more than one pathway for current to follow.
If one pathway is broken (open) the current can continue to flow through the unbroken (closed) paths.
In a parallel circuit, the resistance in each branch/path can be different - depending on the resistors.
Adding or removing resistors on one path does not affect the other paths.
Uses for Parallel Circuits
Most buildings use parallel circuits.

7. Series Circuit
Parallel Circuit

8. Practice! Identify which is series parallel:
What happens to series and parallel circuits when the voltage is increased?
Do you understand circuit drawings?