1.05 Voltage and Resistance.

Why does the current flow?

We will look at this question in more detail in the next section, but for the moment we take a very simple view.


An electrical power supply such as a battery, produces a voltage. Voltage causes current to flow in an electrical circuit. The larger the voltage is, then the larger the current will be. i.e. A 6V battery will produce more current in the same circuit, than a 1.5V battery would. (This would be very apparent because the bulb would glow brighter using the 6V battery.)


Current will flow very easily through some materials, (e.g. copper), but it is very difficult, to cause current to flow through other types of material, (e.g. p.v.c.). i.e.

We can describe this property of a material either as its conductance, ( i.e. how well it allows electrical current to pass through it), or its resistance, (i.e. how well a material resists current flow). Both characteristics, are just a different way of looking at the same property of the material. Resistance is referred to more commonly in d.c. theory. Resistance is measured in units called Ohms (Ω). The copper wires in the circuit will typically have a resistance of less than 1Ω , while the pvc insulation, will have a resistance of several Meg-ohms,(M Ω) (millions of ohms).