Electricity

CONDUCTORS

Are MATERIALS that allow charges That allow charge to easily FLOW

Most common Metals Graphite

INSULATORS

In INSULATORS electrons are ANCHORED to the atoms they can move BUT cannot flow

Glass Wood Plastic Rubber

....

This makes them VERY POOR conductors

InterrupterPush-to-make

Switches

are used to open or close an electric circuit

There are many different types:

Push-to-break

Current Electricity

For a current to flow Charges must be PUSHED By using a battery cell Before they can flow The switch must be closed

When the switch is opened The current stops

Current Intensity

The Current Intensity

Unit:

Is a measure of the flow of charge around a circuit

coulombs/second

It is the number of coulombsThat pass each point in the circuitEvery second

c/s

As is often the case in scienceA compound unit is replaced by a single wordIn this case the ampere or amp

amps

Although electrons flow from

- +

- +

BY CONVENTIONCURRENT FLOWS FROM

+ -1 coulomb every second

= 1 amp

The Current is measured Using an ammeter

A

It is connected in series

A

A

Current Intensity The current depends on the voltage

1 amp = 1coulomb/sec

The bigger the voltage

A

2 amp = 2coulomb/sec

The bigger the current The brighter the light bulb

1 cell 2 cells

The cell (or battery)

Provides the voltage Which helps to push charge aroundthe circuit

Cathode Anode-------

+++++++The voltaic cell

consists ofThe electrodes are DIFFERENT metals

The build up of charge results inA DIFFERENCE in

Two electrodesImmersed in an acidThese react with the acid

This causes the more reactive metal

To acquire negative charge

And the less reactive metal

To acquire a positive charge

Electrical potential energy

Between the electrodesThis is also called theE.M.F or (voltage)

The cell

The voltage produced by a cell

This combination of electrodes

Depends on the materials used for the electrodes

The common alkaline cell is made of

Zinc Anode

Alkaline electrolyte

Manganese Oxide Cathode

Results in an E.P.D. (Voltage)Of about 1.5 V

The battery

As the word suggests,Is a combination of cellsConnected in series

The 4.5 V flat packIs 3 x 1.5 V cellsConnected in series

Electrical Potential Difference

Is measured using a voltmeter

V

Voltmeters are connected in parallel

6V Cell

6V

V

V

6V

Circuit symbol

Resistance

ALL CONDUCTORS have resistance

The electrons collide with vibrating atoms as they moveand this generates heat

it is the opposition to the flow of charges

as they pass through a conducting material

and the conductor gets hot

Resistance Depends on

The dimensions of the conductor

Thin conductor

bigger resistance

Thick conductor

smaller resistance

Short conductor

smaller resistance

Longconductor

bigger resistance

Nichrome

Resistance Depends on

The conductor material

Iron

Has more resistance than

Iron

Copper

Has more resistance than

Nichrome

Resistance

If you want a conductor to change electrical energy into heat Use a HIGH resistance material

or

Tungsten

Aluminium

Resistance

If you DON’T want a conductor to change electrical energy into heat Use a LOW resistance material

or

Copper

Light Bulbs

have high resistancesThey change

ElectricalEnergy

HeatEnergy

LightEnergy

Connecting light bulbs: IN SERIES

Each time a light bulb is connected in SERIES

The resistance in the circuit INCREASESA smaller current flowsThe light bulbs grow dimmerIf a light bulb blowsAll the light bulbs turn off

A1 amp0.5 amp0.33 amp

E.P.D. in series circuits

The sum of the E.P.D across each component

Cell EMF= 6V

V6V

Equals The EMF of the cell

V3V 3V

V2V 2V 2V

Connecting light bulbs: IN PARALLEL

Each time a light bulb is connected in PARALLEL

The current flowing in each light bulb is unchanged

A

The brightness of each light bulb is unchanged

1amp 1amp 1amp

1 amp2 amp3 amp

The current taken from the battery increasesIf a light bulb blows

E.P.D. in parallel circuits

Each time a component is connected

6V

The EPD across it equals The e.m.f. of the cell

emf = 6V

V6V

V6V

V