1. Circuit Diagrams
Circuit diagrams use symbols to represent the different components of an electric circuit
The most common components of simple electric circuits are
batteries
wires
light bulbs
resistors
switches

2. Types of Electric Circuits
Components in an electric circuit can be organized in two fundamentally different ways
Series circuits
all of the components are lined up in a single loop
there is only one path for current to flow through
Christmas-tree lights use series circuits
Parallel circuits
some of the components are in branching loops
there are multiple paths for current to flow through
most household circuits are parallel circuits

3. Series Circuits

4. Series Circuits In a series circuit:
The total current is the same as the current in the individual resistors (there is only one loop and the current has to be the same everywhere in it) IT = I1 = I2 = I3 = etc.
The total voltage is the sum of the individual voltages (each resistor uses only part of the battery voltage) VT = V1 + V2 + V3 + etc.
The total resistance is the sum of the individual resistances (the current has to go through all of the resistors) RT = R1 + R2 + R3 + etc.

5. Parallel Circuits

6. Parallel Circuits In a parallel circuit:
The total current is the sum of the individual currents (only part of the total current flows through each resistor) IT = I1 + I2 + I3 + etc.
The total voltage is the same for each resistor (each resistor is connected directly to the battery) VT = V1 = V2 = V3 = etc.
The reciprocal of the total resistance is the sum of the reciprocals of the individual resistances (multiple resistors allow more current for the same voltage) 1/RT = 1/R1 + 1/R2 + 1/R3 + etc.

7. What Happens When… You add a light bulb to a…
series circuit – the existing bulb(s) get dimmer (the voltage at the existing bulb(s) is reduced)
parallel circuit – the existing bulb(s) do not change (the voltage at the existing bulb(s) is unchanged)
A light bulb burns out in a…
series circuit – the remaining bulb(s) go out (the circuit is now an open circuit)
parallel circuit – the remaining bulb(s) stay on (each light bulb is connected directly to the battery)

8. Electric Power and Energy
Electric power is the rate at which electric energy is used
It is equal to the voltage times the current P = V x I
Power is measured in Watts (W)
Electric energy is equal to electric power times time E = P x t
Household electric energy usage is expressed in kilowatt-hours [kWhr]