electricity 1 primary pupils
DESCRIPTION
electricity, primary scienceTRANSCRIPT
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