Section 8. Electricity

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: electron flowElectricity: Electrons moving from – to +

+ Battery -

= electron

Current in a circuit: current direction

+ Battery -

BEWARE!!!

Electron flow: from – to +Conventional current: from + to -

Electron flow direction

Conventional current direction

Current in a circuit: schemes

+ Battery -

Drawing Scheme

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

Potential difference (voltage)Placing of voltmeter: over the circuit

V VV

V V

V

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)

Refresher exercises:

Paragraph 1: 1, 3Paragraph 4: 3

Paragraph 5: 2 a, b, cParagraph 7: 1, 4

Exercises