- #1
mkienbau
- 12
- 0
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?
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
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