Chapter 12 Lesson 4-Electricity
Vocabulary
1. Electricity-
2. Static electricity-
3. Grounding-
4. Electric current-
5. Circuit-
6. Resistor-
NOTES
What is static electricity?

Electricity is measured in joules (J).

We use units called volts (V) to measure how strongly electrons move.

Protons have a positive charge (+).

Electrons have a negative charge (-).

Particles with opposite charges are attracted to each other.

Particles with the same charge are repelled from each other.

When two objects rub against each other, electrons are sometimes knocked off one object and
onto the other (static electricity)

Attractive force between electrons and protons is strong.

S.E. causes electrons to jump through the air toward nearby protons.
o
A spark is formed.
o
Electrons have been discharged and returned to the protons.
o
Objects are now neutral.

A neutral object has equal numbers of protons and electrons.

Static cling-two oppositely charged objects that stick together.

Charged objects can also attract neutral objects.
o
It pulls on one type of charge and pushes on the other.
o
The neutral object will act like it is slightly charged on one side and attract the charged
object.

When static electricity forms on a good electrical conductor the charges can move freely.

Like charges will push on each other and spread themselves out.

When static electricity forms on an electrical insulator, charges cannot move freely.

Earth is a large neutral conductor.

Protect objects from static electricity/lightning by grounding them to Earth with a wire.

Grounded objects pass their charge onto Earth.

The charges then can spread out so that they are barely noticed.
How can electricity flow?

The path of a circuit consists of wires.

Circuits must also have a device to move electrons along the path.
o
Such devices increase the volts of electrons in the circuit and are called voltage sources.

EX: Batteries

A switch is a device that can open or close the path.

When the switch is closed, the voltage pushes on the electrons in the circuit.
o
This causes electrons to move.
o
Protons feel a force in the opposite direction.
o
Protons are not free to move.

Electricity does not flow the same way through every part of a circuit.

Resistance is measured in units called ohms (Ω).

Electrons lose energy when moving through a resistor.
o
This energy can be transformed into heat or light.
o
A light bulb is a resistor.

Electric current in a circuit travels fast.

Electrons travel just a few millimeters per second.
o

Electrons only need to move far enough to push another electron.
The amount of electric charge moving in a circuit is measured in units called amperes or amps
(A).

There are about six billion electrons moving every second in one amp of current.

Current as small as 0.05 A can seriously hurt you.
What kinds of circuits are there?



Series circuit-if there is only one conductive path.
o
The resistance increases with each resistor added.
o
Electricity travels through all the resistors one after another.
o
As resistors are added, the energy each resistor receives is decreased.
Parallel circuit-more than one conductive path.
o
The overall resistance of the circuit is smaller and more current will flow.
o
Electricity flows through all paths in a parallel circuit at the same time.
o
The smaller the resistance of the path, the more current flows through it.
o
If one path is broken the current will flow through the reaming paths.
Short circuit- a path with little or no resistance that connects the two ends of an electrical
source.
o
Tiny resistance in short circuits causes large currents to flow across them.
o
The large currents can damage appliances, or start fires.
o
Frayed wires are a common cause of short circuits.
How can you use electricity safely?

Plugging too many appliances into a power strip dangerously heats wires.

Each time an appliance is plugged in, another branch is added to the parallel circuit.
o
This increases the current and can lead to fires.

A fuse is a wire that breaks if too much current flows through it.

A breaker is a switch that opens when it detects too much current.

Homes have separate fuses or breakers for different circuits.

Surge protectors prevent sudden spikes in current from entering electronics and damaging
them.

Outlets have small buttons saying “test” and “reset”.
o
These are part of a ground fault interrupter (GFI).
o
GFI is sensitive to changes in current.
o
Will turn an outlet off if a short circuit forms.
o
Will also turn the outlet off if electricity starts to flow through water.

Never reach up into power lines to get a toy that is stuck there.

If you touch two power lines at the same time, or one power line and the ground, it can be
deadly.