• The delocalised electrons are free to move through the crystal structure. 
• When metals are connected to a power source, the electrons all drift in the same direction which creates an electric current (flow of charge at a certain rate).

• Length
• Thickness
• Temperature
• Type of material (resistivity)

• An ammeter has VERY LITTLE RESISTANCE. 
• An ammeter is always connected in SERIES with components in a circuit, as it must allow all the current to flow through it in order to measure current. 

• A voltmeter has GREAT RESISTANCE. 
• A Voltemeter must therefore always be connected in parallel with a component in a circuit, in order to measure the difference in potential energy between two points right before and after a resistor. 

• Potential difference (pd) versus voltage: 
• pd - it emphasises that we are measuring a change in “push” between two different points in an electric circuit (rather than “push” at one point).

• Electromotive force (emf) is a term for pd across sources of electrical energy/batteries. 

• Cells becoming 'discharged' - charge is not used up; the energy is transferred.

• Conventional current:
  - This flows (by definition) from positive to negative around the external circuit 
  - Inside the cell chemical reactions ‘pump’ charge carriers to the terminals. 
  - Some may say that ‘physicists got it wrong because we now know that electrons flow the other way.’ 
  - But it is really an arbitrary choice. 
  - One can illustrate this by looking at current flow and movement of charge carriers in an electrolyte (or an ionized gas). 
  - Positive ions go one way, negative ions go the other way. 
  - And so, however current is defined, there are always examples where current direction and charge carrier movement are opposite.

• Current flows all around a circuit: including through the cell itself.

• A useful analogy for charge flow:
  A Bicycle Chain!
  - This transfers energy from you (equivalent to the cell) to the rear wheel.
  - The chain is not used up (neither is charge),
  - and does not disappear when you run out of energy (when the cell runs flat and the chemical reactions within it stop).
  - It has no beginning and no end.
  - It moves as a SYSTEM, every part all at once.
  - this is the CYCLIC SIMULTANEOUS MODEL OF ELECTRIC CIRCUITS. 

• Another analogy:
• Skiers (charges) being lifted up a mountain by a ski lift (external energy source/emf/cell) and then skiing down a slope (resistor). 
• This is useful for the idea of voltages in parallel circuits. 
• Parallel slopes drop different skiers through the same vertical height (equal voltages across components in parallel).

1. Generation
2. Transmission
3. Distribution to consumers

1. The heating effect
2. The magnetic effect
3. The chemical effect

• It causes a breakdown of the chemical (aqueous salt e.g. copper chloride) into its constituents parts (e.g. copper chloride breaks into copper metal and chlorine gas).

1. SOURCE OF ENERGY
2. PATH FOR ELECTRONS TO FLOW
3. RESISTOR (DIVICE TO CONVERT ELECTRICAL ENERGY TO LIGHT OR HEAT OR SOUND ETC.)

• Tungsten is a metal as heavy as gold (density 19.3 g /cm³),
• as hard as diamond (in the form of tungsten carbide) and
• so heat-resistant, that iron is already boiling before tungsten even melts (melting point: 3422 °C).
• Tungsten has the highest melting point of all metals, making it ideal for high temperature applications in energy and lighting technology, as well as aerospace industry.
• Given its very high density, comparable to that of gold, it is used as a gyrating mass, counterweight or for vibration damper in aerospace, automotive, sport and telecommunications technologies.

• 1 kWh refers to the use of 1 kW of electricity for 1 hour.

• 1 kWh is equivalent to 3 600 000 J of electrical energy:

• 1 kWh = 1 000 W × 1 h = 1 000 W × 3 600 s = 3 600 000 J

Electrical consumption is charged per kWh used.

EXAMPLE 1:

Suppose a 1100 W electrical iron is used for 4 hours and the cost of electrical energy is 61c per kWh. What is the cost of using the iron for 4 hours?

Cost = Power rating of appliance (in kW) × time used (in hours) × price per kWh

         = 1,1 kW × 4 hours × 61c = 268,4c = R 2,68


EXAMPLE 2: 

 An electric kettle has a power output of 2,2 kW 240 V. 

a) Calculate the current in the kettle.

b) Calculate the resistance of the kettle element. 

c) Calculate the cost of using the kettle for 5 hours if the cost per kWh is 61c.

1/R_// = 1/R₁ + 1/R₂ + 1/R₃