Solve 5 Wire Junction Current w/ Conservation of Current

[cse63146]

Homework Statement

The information about the magnitudes of the current density and the diameters for wires 1, 2, 3, and 4 is given in the table. Some of the values are unknown.
Wire Current density (A/mm^2) Diameter (mm) Total Current (A)
1-------- 1.6 -------- 2.0 -------- ?
2 -------- ? -------- 3.0 -------- 2.0
3 -------- 3.0 -------- 1.1 -------- ?
4 -------- 0.8 -------- ? -------- 4.0

What is the current at the 5th wire?

Homework Equations

I know you need to use the conservation of current, but I'm just not sure what formula to use.

The Attempt at a Solution

 

[usman27]

study kirchhoff's junction law...
J = I/pi*r^2 ; pi = 3.14...
Hope this helps... good luck.

 

[cse63146]

would I need to convert the current density and diameter to metres before calculations?

 

[ravi1611]

it I5 is going to be-9.84

 

[cse63146]

it I5 is going to be-9.84

Yep, that's the answer I got, just wasnt sure if it was right. Thanks.

 

[usman27]

yes... always go meters for length unless otherwise specified!
and yess the answer is -9.9

 

[cse63146]

in this case, I didnt convert; I just left it as it

 

[usman27]

That is because the diameter is in (mm) so is the current density :)

 

[cse63146]

That is because the diameter is in (mm) so is the current density :)

Ah, good to know. I probably would have done this on the test without noticing. You probably saved me a few marks, Thanks.