Electricity Help!!

[StankCheeze]

Anyone know a lot about electricity and formula related stuff? I am stuck on a stupid ass online homework question that is stupid and easy and when i put the right answer in it says no. i have 1 guess left until i am penalized...so ...help heres the question with a formula! you just plug in the numbers...but..its stupid!!!


Resistance =

resistivity of material * length of wire / cross sectional area of wire

resistance is in ohms

1 inch = 2.54 cm
100 cm = 1 meter

You wish to make 13 ohm electric heating coil from 18 gauge nichrome wire. The resitivity of nichrome is 1E-4 ohm-cm and the cross-sectional area of 18 gauge wire is 0.001276 in^2.

What length of wire in meters is needed? _________ meters


fill in the meters part please!!!!

 

[StankCheeze]

BUMP! HELP!

 

[Wizkid]

1070 metres?

 

[RossGr]

That is the correct answer for cm,10.7m though. if you do not understand where it came from the whole point of the problem is missed.

First of all this is a pretty simple algebra problem and if you are haveing trouble with that aspect of your course you may want to consider finding a math tutorial.

Let R = Resistance
RV = Resistivtity
CA = Cross Sectional area
L = Length


The first step in this problem is to convert the Area to cm^2, get everything in the same units.

You are given
R = L*RV/A

solve for L

L = R*A/RV

plug in your numbers.

You always want to check the dimemsions of your result

R = ohms
A = cm^2
Rv= ohms*cm

so R*A/RV = ohms*cm^2/ohm*cm = cm

so the result is in cm, surely you can do the conversion to m?

 

[Wizkid]

StankCheeze: maybe your error was converting square inches to square centimetres, 1 inch = 2.54 cm, but 1 inch squares = 2.54^2 cm^2... so 1 inch^2 = 6.45 cm^2...?

 

[Passions]

Everyone has trouble with algebra time to time, here is a detailed explanation:

The Length of wire is described by L=R*A/Rv

A= 0.001276 x 6.4516/1= 0.008232 cm^2

Therefore,
R= 13 Ohms
A= 0.008232 cm^2
Rv= 1x10^-4 Ohm-cm

L comes out to be 1070.19 cm. Convert to m, that brings you to 10.7019m.

 

[TBP]

I wonder why we need in. when the rest of the world are using cm.

 

[Deceiver]

because we are stubborn and don't want to conform to the rest of the world

 

[Bleep]

Hey I was not happy when they went from Cycles to Hertz or from MicroMicro farads to Picofarads
Bleep

 

[PowerJoe]

Amen to that, Deceiver

-PJ