Series & Parallel CircuitsChapter 23

23.1 Simple Circuits

• Water moving down a mountain river• The water goes down the mountain

because of a difference in gravitational potential energy

• The water represents electrical current• The electric current moves through a

circuit because of a difference in electric potential

Series Circuits

• A circuit that has only one path for the current to flow

• Remember that charge cannot be created or destroyed and current is amount charge moving per second

• The potential difference is shared by each device in the circuit.

• Also call voltage drop because as the current passes through each device uses some of the total voltage until it is all used up

I & R in a series circuit

• In an electric circuit, the increase in voltage provided by the energy source (battery), Vsource, is equal to the sum of the voltage drop across the devices

• Vsource=VA+VB+…

Equivalent Resistance in a Series Circuit

• The equivalent resistance is the one resistor that could replace all the resistors of the circuit and keep the same current

• In a series circuit the resistance adds

• R=RA+RB+…

• The equivalent resistance is greater than any individual resistor

Voltage drop in a Series Circuit

• As current moves through any circuit the net change in potential must equal zero

• Gains in the energy source and loses as current passes through the resistors

Voltage Divider

• Used to change a higher voltage to a lower voltage as the current passes through a device.

• Source is 12 V and device required 9 V• A resistor is placed in series with the

device to use the extra 3 V

Parallel Circuits

• More than one path for the current to flow

• Similar to a mountain river and breaks off into three different rivers.

• All three have the same starting and ending gravitational potential energy

• The total river current has to be split into three separate paths

Resistors in a Parallel Circuit

•V=VA=VB…

•I=IA+IB+…

BA R

V

R

V

R

V

BA RRR

111 Equivalent resistance for a parallel circuit