section 8. electricity. refresher year 2 topics: conductors / insulators current in a circuit...
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Refresher year 2Topics:• Conductors / insulators• Current in a circuit• Circuit schemes• Potential Difference (PD)• Resistance
Conduction and insulationElectricity is caused by moving electrons
Conductor: material that lets electrons passInsulator: material that blocks electrons
Conductor InsulatorIron WoodMercury PlasticGraphite (pencil) DirtWater with dilluted salts
Pure water
Current in a circuit: current direction
+ Battery -
BEWARE!!!
Electron flow: from – to +Conventional current: from + to -
Electron flow direction
Conventional current direction
battery ammeter
lamp voltmeter
switch (open)
Resistor or device
traveler switch
power socket
Current in a circuit: schemesSymbols you have to know:
A
V
Potential difference (voltage)Energy of electrons in a circuit:
Potential difference (PD)
Most power sources have a fixed PD
PD can be measured with a voltmeter:
V
Potential difference (voltage)6V
2V ??4V
Bulbs in series: formula
Vtot = V1 + V2 + V3 + …
or in words:
Total voltage = sum of partial voltages
So, remember:Current: amount of electrons flowingPotential difference: ‘energy’ of the electrons
Physical quantity
Symbol Unit Symbol
Current I (capital i) Ampere A
Potential difference
PD Volt V
ResistanceResistance: ‘friction’ on electrons
Physical quantity
Symbol Unit Symbol
resistance R ohm Ω (omega)