Series and Parallel Circuits

2

Circuit Defined

A circuit is a path for electrons to flow through. The path is from a power source’s negative terminal, through the various components and on to the positive terminal Types

Series Parallel Combination

                                       

3

Components - Source

DRY CELL

a source of electrical energy

++

--

4

Components - Load

LIGHT BULBLIGHT BULBlights up whenlights up whenelectricity pass throughelectricity pass through

5

Circuit - CompleteSource of electrical energySource of electrical energy

++

--

AppliancesAppliances

Complete circuitComplete circuit

Electricity flowsElectricity flows

6

Terms to Know

Open circuit – there is a break somewhere and electricity cannot flow (maybe the switch is open)

Closed circuit – electricity can flow (the switch is closed)

Short circuit – the electricity completes a circuit without going through the load

Load – what is using the electricity

7

Schematics

Circuit diagrams, also called schematic diagrams, provide a graphic representation of an electric circuit using standard symbols.

8

Diagram Symbols

wire or conductor

resistor or other load

bulb voltmeter

battery ammeter

switch generator

V

A

9

Example – Simple Circuit

circuit diagramcircuit diagram

+

-

A

+ -

A

10

Complex Circuit

Construct theConstruct thecircuit diagramcircuit diagram

+

-

A

+ -

A

CircuitsCan either be series or parallel.

SeriesCurrent only takes one path for electrons

Current flows through every part of the circuit

Lights in a Series

SeriesIf you add a resistor (like another light):Total resistance goes UP since all the current has must go through each resistor.

Adding Resistors to Series:Current in the circuit will go DOWN (lights will dim)

If you remove a light bulb or one burns out—all go out!

Current in Series

Current is the same at all points

Use Ohm’s Law to find current using resistance and voltage

Voltage in Series

Voltage is reduced by each resistance – voltage drop

Resistance in SeriesAdd up all resistors to get totalTotal resistance will go up because all of the current must go through each resistor.

Sample Problem #1 Draw a series circuit with two 1.5

V batteries, 3 resistors, and a current of 0.5 A.

1. What is the total voltage of the circuit?

2. What is the resistance of each resistor?

Parallel CircuitsHas at least one point where current divides

More than one path for current to flow

Paths are also known as branches

Lights in Parallel

Parallel:If you add a resistor:

Total resistance goes down

Total current goes up when you add another path

Removing a Light BulbIf you remove a light bulb or one burns out, the others stay on because the circuit is still closed.

Current in Parallel Current flows into a branching point, the same total current must flow out again

Current depends on resistance in each branch

Voltage in Parallel

Voltage is the same across each branch – because each branch is on the same wire

Resistance in ParallelCalculate current in each branch based on resistance in each branch by using Ohm’s Law

Practice problem #2

Draw a parallel circuit with two resistors (one on each branch) and a 12 V battery.

1. What is the voltage through each resistor?

Toll Road—Circuit Analogy

Toll Booth ExplanationAdding toll booths in series

increases resistance and slows the current flow.

Adding toll booths in parallel lowers resistance and increases the current flow.

Batteries in Series and Parallel:

In series—The voltage is increased.

In parallel—No change in voltage; these batteries will last longer!

One More FINAL Thing:

Two Types of Current:DC—Direct Current—produced by solar cells and chemical cells (batteries)

Current only flows in one direction.

2nd type of current:AC—Alternating CurrentCurrent flows back and forth (alternates)

Found in homesGenerators produce AC current