ELECTRICITY

Review – The Atom

All matter is made of tiny particles called atoms.

Atoms are made of 3 different types of particles:

1. Protons2. Neutrons3. Electrons

Review – Atomic Structure

+

-

-

Electron

NeutronProton

Nucleus

Review – Atomic Charge

A neutral atom has the same number of protons as electrons.

Eg. A neutral oxygen atom has 8 protons and 8 electrons.

Review – Atomic Charge

Electrons can be removed from an atom, resulting in a positively charged atom.

-

-

+

+NeutralPositive

Review – Atomic Charge

Electrons can also be added to an atom, resulting in a negatively charged atom.

-

-+NeutralNegative

-

Review – Atomic Charge

An atom with an uneven number of protons and electrons is called an ion.

Electrons can be separate from atoms and can move freely within and between certain substances.

This is why metals conduct electricity.

What is Electricity?

Electricity is a convenient type of energy that travels very fast and can be transformed into a variety of other types of energy.

Types of Electricity

There are two types of electricity.

Static Electricit

y

Current Electricit

y

Static Electricity

Static E occurs within insulators.

When the insulator is rubbed electrons are either added or removed, and the object is charged.

+

-

Static Electricity

When a plastic rod is rubbed with a wool cloth, the rod will lose electrons to the cloth and become positively charged.

The wool becomes negatively charged.

+

+

+

+

+

+

-

-

- -

-

-

Static Electricity

Static electricity is caused by a surplus or deficiency of electrons in an object.

The object holds storedelectrical energy.

-

--

--

-

Static Electricity

If two objects have opposite charges they will attract each other.

If they have the same charges they will repel.

+-

--

+

++++

+

+

+

+

++

+-

- - --

-

-

-

--

-

-

-

Current Electricity

Electrical currents happen when free electrons travel from an area which is negatively charged to an area which is positively charged.

Electricity needs a continuous pathway (circuit) in order to flow.

Current Electricity

A substance like copper has free electrons and is an electrical conductor.

Plastic is said to be an electrical insulator because it does not have free electrons.

Circuit Diagrams

Component

Symbol

Wire

Single Cell

Battery of Cells

Open Switch

Closed Switch

Lamp

Fuse

Current Electricity

A circuit consists of at least 3 main parts:

1. An energy source (e.g.. battery).2. An energy user (e.g.. light bulb).3. A complete conducting pathway

(wires)

Circuit Diagrams

Draw a simple circuit showing one light bulb controlled by a switch and powered by 2 cells.

Measuring Current

When electrons flow around a circuit they create current.

We can measure the amount of electrons flowing in a circuit with an ammeter.

The symbol for current is I, because it describes the intensity of the current.

Measuring Current

The ammeter measures in units called amperes (or amps) and is representedby the symbol A.

In circuit diagrams we represent an ammeter by the symbol:

A

Current

A

- -

Measuring Current

An ammeter must be connected in series at the point where you wish to measure the current.

A

Types of Current

There are 2 types of current:

Direct Current (DC) – Electrons flow in only one direction. (E.g. Battery powered devices)

Alternating Current (AC) – Direction changes 50 times a second. (E.g. Electricity from mains)

Measuring Energy

Current in a circuit carries electrical energy.

Electrons gain energy from the energy source and lose energy from the energy users, where it is converted into other forms.

Measuring Energy

Voltage gain – the increase in electrical energy.

Voltage loss – the decrease in electrical energy.

We represent the gain or loss in voltage by the symbol V.

Measuring Energy

The unit for voltage is the volt and can be measured with a voltmeter.

In circuit diagrams we represent an voltmeter by the symbol:

V

Measuring Energy

A voltmeter can only measure the change in voltage so it must be connected in parallel around a lamp or battery.

V

Measuring Energy

The amount of voltage lost at an energy user is equal to the amount of voltage gained from the batteries.

In a series circuit the voltage loss is shared between components.

In parallel the voltage loss is the same in both components.

Electrical Conductors

Conductors are materials that allow the flow of electric charge. Metals are good conductors.

Insulators are materials that do not allow the flow of electric charge. Plastic is an example of a good insulator.

Electrical Conductors It is the delocalized electrons

involved in metallic bonding that allow metals to conduct electricity.

The delocalized electrons are free to flow through the metal and so carry a current.

Insulating materials do not contain free electrons and so current is unable to flow.