johnny_t said:If you are talking about a length of wire, then three main factors affect the resistance: The conductivity of the metal, the cross-sectional area of the wire and the length of the wire. Given that you can't do much about the conductivity (unless you're talking about hi-fi cable or similar, then maybe go for gold cable instead of copper, though I've never been entirely convinced by the benefit), a fatter wire will have less resistance than a thin one, a longer wire will have more resistance than a short one. Other factors come into play, such as temperature, but they are the main ones.
As for how its measured, the short answer is with a multimeter. As for how they do it, they apply a voltage, measure the current, and then work it out by dividing the voltage applied by the current flowing for a digital one. An analogue one does the same, but just has a needle that moves with current, and the scale adjusted to convert that to resistance.
Qedelec said:Then there is the factor of negative coeficient of resistance where temperature increase causes a decrease in resistance such as used in thermistors.
If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.
Select the supplier or trade you require, enter your location to begin your search.
Are you a trade or supplier? You can create your listing free at DIYnot Local