All online and my tables stop at 50 SWG. I don't know if the standard copper
resistivity formula breaks down over/less than 50 SWG. Wire in question ,
measured optically to about 0.05 mm diameter as too fine to mike up. About
19.7 ohm per metre but what is that in AWG or SWG ?

N_Cook wrote:

All online and my tables stop at 50 SWG. I don't know if the standard copper
resistivity formula breaks down over/less than 50 SWG. Wire in question ,
measured optically to about 0.05 mm diameter as too fine to mike up. About
19.7 ohm per metre but what is that in AWG or SWG ?

As a last resort, you could try drawing a graph of diameter or
diameter-squared against SWG, AWG or resistance. If you can find a
straight-line relationship, you can extrapolate to any value you need.

I think you can still buy graph paper, rulers and pencils in shops - if
you can find any shops. :-)

--
~ Adrian Tuddenham ~
(Remove the ".invalid"s and add ".co.uk" to reply)
www.poppyrecords.co.uk

In article , "N_Cook"
wrote:

All online and my tables stop at 50 SWG. I don't know if the standard copper
resistivity formula breaks down over/less than 50 SWG. Wire in question ,
measured optically to about 0.05 mm diameter as too fine to mike up. About
19.7 ohm per metre but what is that in AWG or SWG ?

www.mwswire.com has tables down to 55 AWG. By my math, your resistance
figure translates to about 6000 ohms per 1000 ft., which would put it in
the 48 AWG category.

Diameter is going to vary significantly based on insulation.

..05 mm is about .002". If your micrometer can't measure that, you need a
better micrometer.

On Mon, 15 Aug 2011 15:12:37 +0100, "N_Cook" put
finger to keyboard and composed:

All online and my tables stop at 50 SWG. I don't know if the standard copper
resistivity formula breaks down over/less than 50 SWG. Wire in question ,
measured optically to about 0.05 mm diameter as too fine to mike up. About
19.7 ohm per metre but what is that in AWG or SWG ?

Resistivity is calculated according to the following formula:

rho = R x A / L

where ...

rho = resistivity = 1.68e-8 ohms/metre for copper
R = resistance
A = cross-sectional area
L = length of material

http://en.wikipedia.org/wiki/Electri...d_conductivity

Therefore ...

A = rho / (R/L) = 1.68e-8 / 19.7

A = pi x r^2 = pi x (dia/2)^2

dia = 2 x sqrt(A / pi) = 2 x sqrt(1.68 x 10^-8 / 19.7 / pi)
= 0.03295 mm

http://www.google.com/search?&q=2+x+...-8+/+19.7+/+pi)


According to the tables, your wire size appears to be 49 SWG.

http://en.wikipedia.org/wiki/Standard_wire_gauge

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.

"Nutcase Kook"

All online and my tables stop at 50 SWG. I don't know if the standard
copper
resistivity formula breaks down over/less than 50 SWG. Wire in question ,
measured optically to about 0.05 mm diameter as too fine to mike up. About
19.7 ohm per metre but what is that in AWG or SWG ?


** Last time I dealt with fine enamelled wire like, that it was from the
high impedance (output end ) transducer of an Accutronics reverb unit.

But the finest I have seen is on the coil of an AKG D19 ( 200 ohms) mic
capsule - about 0.03 mm.

The D19 diaphragm was sold as a spare part and used in other mics, like the
original D12.



...... Phil