Resistance
- Thread starter KDOE
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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.
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.
johnny_t said:
Then there is the factor of negative coeficient of resistance where temperature increase causes a decrease in resistance such as used in thermistors.
Perhaps we should leave out super conductors
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Let the college kid work it out for himself!
Far too many kids won't lift a finger (or even read a book) to get the answer.
He could use Google but he's too idle to do that!
He'll never make a good apprentice if you spoonfeed him all his life.
Far too many kids won't lift a finger (or even read a book) to get the answer.
He could use Google but he's too idle to do that!
He'll never make a good apprentice if you spoonfeed him all his life.
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2
2scoops0406
Qedelec said:
But not in the case of silicon where an increase in temperature causes an increase in resistance, so called thermal runaway.
Thanks jonney-T ,
Swidonspark, "collage kid", i wish, i am 44, and am about to start "part p" (17 unit) as my knowlidge is limited i am just trying to get some idea of basic princibles from books and anyone who can be helpfull
Swidonspark, "collage kid", i wish, i am 44, and am about to start "part p" (17 unit) as my knowlidge is limited i am just trying to get some idea of basic princibles from books and anyone who can be helpfull
see here: http://www.kevinboone.com/electricity.html for basic electrical theory
......a mere youngster, try 54.
And glad I could be helpful not much us oldies are good at any more.
When I was a boy...................
And glad I could be helpful not much us oldies are good at any more.
When I was a boy...................
Your very welcome KD if I can be of ant further help, drop me a line, addy is in profile. Yes qualified and registered and sole trader. 'She who must be obeyed' plans for us to retire to your part of the country.
Think geek: http://www.thinkgeek.com/tshirts/science/60fd/
Its an amercian site though, I'm pretty sure they ship to the UK, but not sure how much it'd cost after postage...
Its an amercian site though, I'm pretty sure they ship to the UK, but not sure how much it'd cost after postage...
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