why resistor

Yes, it would work, but what a *daft* idea! Sounds like the guy just enjoyed being annoying.

And here is a bigger nit-pick: You use whatever are common or standard measures your country, and others may use what is common or standard in their country.

Don

obvious

concept

not

inductance

seems

did

:)

As mentioned all conductors have some resistance. In many electronic circuits the resistance of the connecting wires or printed circuit material is low enough that it is not usually counted, especially if the current is low, say under an amp or so. If large currents are drawn or under certain circumstances then the resistance of the wire will have to be looked at.

Resistors are made in many ways , some are formulations of carbon and some are wound with wire that has a high resistance for its length. Tolerance is how close the resistance value is compaired to its marked value. Many times a 5 to 10 % differance is ok. Many years ago the resistors were 20 %. Then the 10% resistors became the most often used value. Now I think 5% is very common. Maybe beter ways to make them inexpensive is the reason for that. Many circuits are designed to the 10 % specification. The resistors are made bigger to handle more power. If wire, larger wire is used.

I would not get hung up on them being voltage/current converters at all. They are mostly power wasters and isolators. They let one power supply voltage source do many things. They can also be thought of as restrictors such as when used in a timming circuit with a capacitor.

all resistors are conductors (any that aren't are insulators not resistors)

a 0.00002 mho conductor is a 50000 ohm resistor, the two merely describe the same quantity in a different way.

to convert merely take the reciprocal, if you're using a calculator with a [1/x] button use that, otherwise divide 1 by the one quantity to find the other.

a conductor does not need to be made of metal, as I hinted earlier carbon has a relatively poor conductivity, so if something with a low conductance (or high resistance) is wanted a thin layer of carbon is often used.

to achieve a 50K resistance in metal an extremely long, and/or thin, wire would be needed

by way of comparison a 240V 15W soldering iron (which typically has a nichrome wire heating element - atleast the cheap ones do) has a resistance of only about 4167 ohms. (or a conductance of about 0.00024 mho)

so depending on the dimensions of the wire quite a high voltage would be needed to push enough current through the wire to damage it.

Bye. Jasen

Just a small nit-pick: Please use SI units, where they exist? :) Such as the SI unit for conductance, the 'Siemens' (abbreviated 'S') - which also just happens to be the same size as the 'mho', but which benefits form being an actual international standard.

Best wishes,

// Christian Brunschen

the

did

:)

has

nichrome

oops, should have looked up 'mho' information (pun intended) before question

inverse of ohm (ha) , i had wires in my head from earlier conductor reply and i had invisioned in my head a .00002 diameter wire when i read .00002 mho

well i guess i wasted you time afterall (and again)

thanks for info/replies robb

--- Sure. If you've got a 4 -> 20mA transmitter somewhere, all you have to do is insert a resistor, measure the voltage drop across the resitor, and from:

E I = --- R

you can figure the current flowing in the line.

Also, shunts, (which aren't really shunts but, rather, small-valued series resistances, sigh...) are used to determine the current flowing through them by dropping a small voltage (on the order of millivolts) across them for currents (on the order of amperes to thousands of amperes) through them.

-- John Fields Professional Circuit Designer

The classic example is the inverting opamp configuration used to sum several inputs. Each input resistor is a current scaling factor for its input voltage and the inverting input node is a current summing junction held at a virtual ground by the feedback.

An ohm is just a short hand way of saying a volt per ampere. An ideal resistor is just a mechanism that relates voltage to current with single proportionality constant (its resistance), regardless of the value of voltage or current. Of course, no such ideal device exists, but lots of materials are close enough to this ideal over a wide enough range of currents for very useful approximations of ideal resistors to be manufactured.

Thank you, Peter. Yes, I was doing a play on words. But I wasn't really trying to confuse, I actually thought more people would pick up on the two-descriptions-of-the-same-thing idea. Wasn't trying to be a troll either, I honestly thought more people would appreciate the humorous intent. Oh well.

Regards,

Mark

definition

well i read this purely as a definition per the I=VR equation.

But the concept of voltage/current conversion as a description of resistors seems interesting in my amateur learning mind and kinda helped when thinking about the reason for using resistors with transistors

do you know of a situation where thinking of resistors as convertors would be useful

thaks for replies robb

restrictors

resistors

thinking

While I still don't really think of the resistors as converters, I can tell of one application where it seems that they are. Where I work there are many devices that measuer parameters such as temperature and pressure. The output of them is a signal of 4 to 20 miliamps . This repersents the zero to full scale output of the device. The signal goes up a pair of shielded wires to a computer. All the inputs of the computer is setup for a signal level of 1 to 5 volts. By putting a 250 ohm resistor across the input terminals of the computer, the 4 to 20 mz signal is 'converted' to a 1 to 5 volt signal.

I use the term computer in a general way. It is in industrial controler that has hundreds of inputs and outputs. Some are also called PLCs.

You mean I = V/R !

Graham