# Homework Help: Diameter of tungsten wire

1. Dec 28, 2011

### Virsnieks

1. The problem statement, all variables and given/known data

If we know, that 200 mm of tungsten wire weights 1.72 mg, then what is the diameter of this wire

2. Relevant equations

3. The attempt at a solution

I by my self came to the conclusion, that the answer is 0.13 mm. But if I take in accordance, that my Algebra and Physics is more than poor... may someone could calculate and prof this.

Thx

2. Dec 28, 2011

### LawrenceC

"If we know, that 200 mm of tungsten wire weights 1.72 mg, then what is the diameter of this wire"

Grams are mass, not weight.

A wire is a long, thin cylinder. Compute volume in terms of diameter, then mass. Solve for diameter.

3. Dec 28, 2011

### Redbelly98

Staff Emeritus
Welcome to Physics Forums.
I calculate something different. If you show us your actual calculations, we can help figure out what went wrong.

4. Dec 29, 2011

### Virsnieks

So I try`d to calculate it one more time this morning whis a fresh head and got some different:
My Idea was to use formula for Desity, to get the Volume and then change the formula for cilinder volumen V=p*r2*h, for getting the radius

200 mm = 0.2 m
1.72mg= 0.00172 kg
Denisty of tungsten = 19250 kg/m3

1. Step. Density = Mass/Volume, so Volume = mass/density

Volume = 0.00172/19250 = 0.000000008935 m3

2. Step. V=p*r2*h; 0.000000008935=3.14*r2*0.2

r=SQRT of 0.000000008935/3.14*0.20
r= 0,0000238559904479939 m
r=0.02385599 mm or the Diameter then would be 0.04771198 mm. This looks better...

Last edited: Dec 29, 2011
5. Dec 29, 2011

### LawrenceC

1.72mg= 0.00172 kg

You are saying that 1.72 milligrams is 0.00172 kilogram???????

6. Dec 29, 2011

### Virsnieks

0.000172 kg - one zero missed... everything else should be correct.

7. Dec 29, 2011

Try again.

8. Jan 1, 2012

### Staff: Mentor

No - mg is not g. What does the 'm' stand for?