Pretty easy ENGE question

  • Thread starter JeeebeZ
  • Start date
  • #1
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1
Pretty easy Circuit question...

So, im in my first year ENGE Class second week in, and im given this diagram

Homework Statement


Basically Im given this Diagram (attachment)

And told to find the total Resistivity if using AWG 18

So, i got

P=800W
E=100V
R=E^2/P = 15.125 Ohms

Homework Equations



So for the Resistivity R = p l/a.

The Attempt at a Solution



But im completly unsure how to get p l & a.

This isn't even a assignment question it was a example done in class on the board, but my instructor just randomly says everything and doesnt explain anything.

So when alls said and done I have

R = 4.13
I = 110/23.5= 4.7 Amps

But absolutly no clue as to how to get it :(
 

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Answers and Replies

  • #3
40
1
So,
p = resistivity of copper = 10.37 CM
l = length of wire = 200m / 0.3048 = 656.17 ft
a = area of 18 AWG = 1624 CM

R = 10.37 * 656.17 / 1624 = 4.18

So then to get I i got

I = E / R
I = E / R1 + R2 + R3
I = 110V / 4.18 + 4.18 + 15.125
I = 110/23.485
I = 4.68

Is there any way i could have done this without having to convert the meters to feet?
 
  • #5
40
1
cm is a unit of length
CM is circular mil

you said they should all be in my text. Everything in my text is based off CM, i dont know why but it is >_<
 
  • #6
203
0
A circular mil(or CM) is diameter is mills squared

OR

1 mil = 0.001 in.

That's what my book says....

Your resistivity(or rowe) should be in Ohms * CM / ft.
 
  • #7
40
1
yah that sounds right, i just dont know how to make symbols on here so well... i didnt @[email protected]
 
  • #8
Astronuc
Staff Emeritus
Science Advisor
19,261
2,748
cm is a unit of length
CM is circular mil
Ah, my mistake. I should have recognized it, but its a unit I now use seldom. 1624 cmil is correct.

If resistivity is given in SI/metric units, one does not have to use feet. The problem in the US is that most engineering is still taught with English/British units, and there are sometimes mixed units.

I use both at work, but prefer metric.
 
  • #9
203
0
I agree.......prefer metric to work problems with.....but still understand english better, when someone yells out a distance or figure or something....
 

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