You need to design a 0.9 A fuse that "blows" if the current exceeds 0.9 A. The fuse material in your stockroom melts at a current density of 540 A/cm2. What diameter wire of this material will do the job?(adsbygoogle = window.adsbygoogle || []).push({});

540x10^-2=5.40 A/m^2

5.40= .9/x

Solving for x gives the answer: .166666666666667

Then:

.166666666667=pi(r^2)

sqrt(.166666666667/pi)=r

The result of that answer multiplied by 2 gives 4.607m. The answer asks for it in mm so I converted to 460.7mm and it says its wrong. Where did I go wrong, I'm just using the current density formula: J=I/A

Where J is the current density

I is the current

A is the area

**Physics Forums | Science Articles, Homework Help, Discussion**

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Homework Help: Finding diameter of a wire based on the current and current density.

**Physics Forums | Science Articles, Homework Help, Discussion**