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why resistor

P

Paul Burridge

Jan 1, 1970
0
No, he was absolutely correct. Read it again carefully.

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

Ralph Mowery

Jan 1, 1970
0
Rob B said:
I did't miss earlier posts i am trying to learn more, i have always found
electronics fascinating, want to learn, and was trying to relate my obvious
limited knowledge of standard resistor attributes/properties to the concept
of wires (i.e. conductors) as resistors.

i read about resistance of wires , that most all wires ( conductors and not
super-conductor) have some resistance depending on several factors,
composition , size ( length , cross sectional area) , shape ( for inductance
issue)

i read about resistors being voltage <-> current convertors via definition
I=VR

but i could not relate tolerance and power rating to resistor wires ?
because the example given of the (0.00002 mho conductor ) as 50k ohm
resistor made me wonder where does one figure the power rating as it seems
like such a tiny wire that would easily melt at least i have have melted
bigger wires in what i thought were prett mild simple circuit

sorry to sound like giving an amateur lesson but i wanted to show that i did
put some time in to researching before wasting your time with a question :)
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.
 
P

Peter Bennett

Jan 1, 1970
0
I did't miss earlier posts i am trying to learn more, i have always found
electronics fascinating, want to learn, and was trying to relate my obvious
limited knowledge of standard resistor attributes/properties to the concept
of wires (i.e. conductors) as resistors.

The original post suggesting the use of conductors in place of
resistors was a sort of "play on words". It was a (fairly successful)
attempt to confuse.

A 1000 ohm resistor _is_ a .001 mho conductor.



--
Peter Bennett, VE7CEI
peterbb4 (at) interchange.ubc.ca
new newsgroup users info : http://vancouver-webpages.com/nnq
GPS and NMEA info: http://vancouver-webpages.com/peter
Vancouver Power Squadron: http://vancouver.powersquadron.ca
 
J

Jasen Betts

Jan 1, 1970
0
I did't miss earlier posts i am trying to learn more, i have always found
electronics fascinating, want to learn, and was trying to relate my obvious
limited knowledge of standard resistor attributes/properties to the concept
of wires (i.e. conductors) as resistors.

all resistors are conductors (any that aren't are insulators not resistors)
but i could not relate tolerance and power rating to resistor wires ?
because the example given of the (0.00002 mho conductor ) as 50k ohm
resistor made me wonder where does one figure the power rating as it seems
like such a tiny wire that would easily melt at least i have have melted
bigger wires in what i thought were prett mild simple circuit

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.
sorry to sound like giving an amateur lesson but i wanted to show that i did
put some time in to researching before wasting your time with a question :)

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
 
C

Christian Brunschen

Jan 1, 1970
0
The original post suggesting the use of conductors in place of
resistors was a sort of "play on words". It was a (fairly successful)
attempt to confuse.

A 1000 ohm resistor _is_ a .001 mho conductor.

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
 
D

Don Bowey

Jan 1, 1970
0
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

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
 
R

Rob B

Jan 1, 1970
0
Jasen Betts said:
[snip]

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.
sorry to sound like giving an amateur lesson but i wanted to show that i did
put some time in to researching before wasting your time with a question
:)

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.

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
 
R

Rob B

Jan 1, 1970
0
Ralph Mowery said:
i read about resistors being voltage <-> current convertors via definition
I=VR
[snip]

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.

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
 
R

Ralph Mowery

Jan 1, 1970
0
Rob B said:
Ralph Mowery said:
i read about resistors being voltage <-> current convertors via definition
I=VR
[snip]

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.

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

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.
 
J

John Popelish

Jan 1, 1970
0
Rob said:
[snip]

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.


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

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.
 
J

John Fields

Jan 1, 1970
0
do you know of a situation where thinking of resistors as convertors would
be useful

---
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.
 
P

Pooh Bear

Jan 1, 1970
0
Rob said:
Ralph Mowery said:
i read about resistors being voltage <-> current convertors via definition
I=VR
[snip]

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.

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

You mean I = V/R !

Graham
 
R

redbelly

Jan 1, 1970
0
Peter said:
The original post suggesting the use of conductors in place of
resistors was a sort of "play on words". It was a (fairly successful)
attempt to confuse.

A 1000 ohm resistor _is_ a .001 mho conductor.

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
 
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