Electric Circuits10.9t

A Complete Circuit

Electrons flow from the source to the load and then back to the source.

The battery is the source that supplies energy to the circuit.

The light bulb is the load where energy leaves the circuit.

The electrons are recycled.

SwitchesThe function of a switch is to start or stop

the flow of electrons.

With the switch closed, electrons can flow and the light bulb is

on!

SwitchesThe function of a switch is to start or stop

the flow of electrons.

When the switch is

opened, the circuit is

incomplete and electrons cannot flow. The light bulb

is off!

The Water Flow Analogy

Compare this with the electric circuit.

What part of this plumbing

circuit is comparable in function to the

switch?

Anatomy of a Flashlight

The circuit must be complete for the bulb

to light up.

Electrons flow from the base of the battery to

the metal strip along the side. If the switch is on, then this strip presses

tightly against the side of the light bulb. Electrons return from the bulb to the top of the battery.

Series Circuits

In a series circuit, there is only one path that current may follow.

What happens to current in the other lamps if one lamp in a series circuit burns out?

Parallel CircuitsIn a parallel circuit, there are many routes that

current may follow.

What happens to the current in the other lamps if one of the lamps in a parallel circuit burns out?

Schematic Diagrams

The series circuit.

The parallel circuit.

Circuits in our HomesHousehold appliances are wired in parallel with

each other.

How do we know this must be true?

Safety DevicesWhen too many devices are plugged into a parallel circuit, it draws too much current from the source.

This is called an overload.

Fuses protect us from overloads

by melting. They break the circuit before a fire can

start.

When Things Go Wrong

When electrical devices stop working, the cause is usually one of two things.

An incomplete circuit.

ORA short circuit.

When Things Go Wrong

Here are two examples of incomplete circuits.

In neither case can the electrons flow

from the source to the load and then

back to the source.

When Things Go Wrong

Here are two examples of incomplete circuits.

Where would you

add a wire to complete

each circuit?

When Things Go Wrong

Why is this circuit incomplete?

What could you do to fix

it?

Troubleshooting

In the real world, incomplete circuits happens whenever something

breaks,

melts,

pulls apart, or

is not assembled correctly.

Troubleshooting

Contrast these two pictures.

good light bulb burned-out bulb

When Things Go Wrong

In a short circuit, there is a path for electrons to follow from the source to the load and back again that has very little

electrical resistance.

This momentarily causes a dangerously large amount of current to

flow. To prevent a disaster, a fuse blows or a circuit breaker shuts the

circuit off.

When Things Go Wrong

Why is this a short circuit?

What will happen in this

case?

How would you fix it?

Quick QuizTwo arrangements of battery, bulb, and wire are shown below. Which of the two arrangements, if

either, will light the bulb? Explain.