Current Electricity

When electric charge moves we call it current electricity. In most cases the charged particle that

moves is the electron, which is negative. Electric current is created by electrons being pushed away

by other electrons or electrons being attracted to protons, which are positive.

How does this happen?

Remember, static electricity can be made by rubbing two different objects together. When this

happens, the person doing the rubbing does work. The work moves electrons from one object to

another.

In this diagram, object A is rubbed with object B. The electrons do not really “want” to go to object B.

Since electrons repel each other, they do not like to be put close together on one object. The

electrons need to be forced or pushed to object B. Friction causes energy to be released when the

objects are rubbed together. This energy is used to push the electrons to object B.

Energy from friction pushes electronsfrom B to A

A

Try this: Rub your hands together quickly. Your hands get hot. This is the energy that is used by the electrons.

A

BB B

A A

Once the electrons get to object B they would like to go back to object A. They cannot because the

space between them is too large. However if we connected A and B with a wire the electrons would

run down the wire back to A. When the electrons run through the wire it is called current electricity.

The problem with our example is that we would have to keep rubbing the objects together to keep

moving the electrons to object B and then allow the electrons to run back to A.

This is a very slow way to make electricity! There are better ways to “force”

electrons to move from one substance to another. Mechanical generators,

batteries and solar cells are just a few examples devices that move electrons

from one place to another.

Small hand crank generators work like this. By turning the handle we make the energy that moves the

electrons. When the electrons run back to where they started from they can run through a device like

a light bulb and make it glow.

Sources of Electricity

BA

B

A

B

A

Batteries

There are better ways of moving electrons than rubbing things together. Chemical energy can be

used to move electrons. In a battery (or cell) a chemical reaction takes place that releases the energy

needed to move electrons from one place to another. In the cell, electrons are taken from the positive

terminal and pushed to the negative terminal. If a conductor is connected to the positive and negative

terminal the electrons will run from the negative terminal, through the conductor back to the positive

terminal.

The figure to the right is a cut-away diagram of a typical

dry cell. In the middle is a metal rod (in this case a carbon

rod). The outside of the cell is made from zinc. Between

the two metals is a chemical mixture that moves the

electrons from one metal to the other. A finished cell is

wrapped with a protective coating.

A cell acts like a pump. It takes electrons from the positive terminal and

“pumps” them to the negative terminal. The electrons run through a

conductor back to the positive terminal and start over again. The problem is

that in a cell it is a chemical reaction that “pumps” the electrons. Once

all of the chemicals have reacted the cell stops “pumping” electrons. When

the chemicals are used up the cell is dead.

Some cells are rechargeable. They contain chemicals that can be returned

to an “unreacted” form when the cell is recharged. DO NOT TRY TO

RECHARGE CELLS THAT ARE NOT RECHARGEABLE. Non-rechargeable

cells may explode if placed in a battery recharger.

Generating Stations

Mechanical energy can also be used to move electrons. Generating stations use a variety of ways to

turn a “turbine” which in turn causes an electrical generator to convert mechanical moving energy into

electrical energy. Electrical energy is produced in generating stations and transported to your home

through wires at very high voltages.

Some types of generation stations:

Hydro Generating Stations

Use falling water to turn the turbine.

Fuel Fired Generating Stations (Coal, Natural Gas)

Use steam heated by the fuel to turn

the turbine.

Nuclear Generating Stations

Use nuclear reactors to heat the

steam that turns the turbine.

Other Types Of Generating Stations

Wind – Wind used to turn the turbine.

Geothermal – Heat from the earth is used to turn the turbine.

Solar- Solar cells are able to change the sun’s energy directly into electrical energy.

Electrons and Energy (Voltage)

You may have wondered what the difference is between a 9.0 volt cell

and a 1.5 volt cell. Inside a cell energy from a chemical reaction is used

to push electrons onto the negative terminal. The electrons on the

negative terminal are pushing each other away, if given a chance they will

run down a wire and through a device to get back to the positive

terminal. As the electrons run back to the positive terminal they will

lose all the energy they had. In science the unit of volts is used to

measure how much energy the electrons in a circuit are carrying.

So the electrons in a 9.0 volt cell have more energy than the electrons in a 1.5 volt cell.

We often call the energy stored in electrons voltage but the proper name is electric potential. We

measure electric potential with a device called a voltmeter.

An easy way to visualize electricity is to think of electrons as little carriers of energy. A source

(battery, generator etc..) gives energy to the electrons. The electrons carry the energy with them and

drop the energy off as they pass through electrical devices. When they return to the source they have

given up all their energy so the source gives them more.

Current

E E E

Current is used to describe how many electrons are moving through an object like a wire. A high

current in a wire means many electrons are moving through the wire and a low current means few

electrons are moving through the wire. We measure current with a unit called amperes (or amps for

short). As an example, 1 ampere of current would flow through a 100 W light bulb. Since electrons

are very small many are needed to make usable current. To get 1 ampere of current 6 250 000 000

000 000 000 electrons must pass through a wire every second! Current is measured with a device

called an ammeter. The table below shows the current used by some common electrical devices.

Electrical Device Electric Current (A)Electronic wrist watch 0.0013

Calculator 0.002

Electric clock 0.16

Fluorescent light bulb 0.5

100 W light bulb 0.83

television 4.1

Electric drill 4.5

Microwave oven 5.0

Vacuum cleaner 6.5

Electric stove element 6.8

toaster 13.6

Clothes dryer 40

Car starter motor 500

Resistance

Not all substances will allow electrons to move through them freely. Resistance is a measure of how

easily electrons can pass through a substance. A substance with a low resistance allows electrons to

pass through it easily (a good conductor). A substance with a high resistance is a substance that is

very difficult for electrons to move through (an insulator).

Conductors are substances that allow electrons to pass through them quite easily. Metals such as

gold, copper and aluminum are good conductors.

Insulators are substances that do not allow electrons to move through them. Rubber, plastic and

wood are good insulators.

Very few substances have absolutely no resistance. Even good conductors have some resistance.

When electrons encounter resistance as they move through a substance they lose energy. The

greater the resistance the greater the energy lost.

LoadsThe electrical energy the electrons lose from resistance is converted into one of four forms of energy:

1. heat energy

2. light energy

3. sound energy

4. mechanical energy (energy of motion)

Loads are devices that have a resistance and remove energy from electrons so

that it can be used in different forms.

For example the heating element on an electric stove has a high resistance. Electrons lose energy as

they pass through it the energy is converted to heat energy.

Incandescent light bulbs contain a very thin wire made of tungsten. The

tungsten wire has a very high resistance. As electrons pass through the

tungsten they release energy in the form of heat. The tungsten becomes so hot

that it gives off a brilliant white light. Tungsten has a very high melting point so it

can be kept very hot without melting or breaking down.

If you were asked to jog down a 100 m long hallway you would use a small amount of energy to get to the other end. If you were asked to jog down a 100 m long hallway with 1.5 m high walls every 5 m that you had to climb over you would work up a sweat getting to the end of the hall. You would lose more energy due to resistance!

Did you know: Electricity may pass through a 100 km of wire on its way to your

house from a generator. Even though the wires are made with good

conductors they are so long that the energy loss is noticeable. Some electricity

Did you know: Electricity may pass through a 100 km of wire on its way to your

house from a generator. Even though the wires are made with good

conductors they are so long that the energy loss is noticeable. Some electricity