Bird on transmission line and force on current-carrying wire

[altrez]

Just two questions that are a small part of my ISU for physics. For this year we had to teach ourselves the unit on electricity and magnetism.

1. A bird stands on an electric tranmission line carrying 1200A. The line has a $1.0\times10^{-5} \Omega$ resistance per metre and the bird's feet are 30cm apart. What voltage does the bird feel.

2. What is the force per metre on a wirde carrying a 2.50A current when perpendicular to a 1.10T magenetic field.

For question one, I was first thinking that since the bird isn't grounded, it shouldn't really feel anything, but since the question probably wouldn't be as easy as that, i guess i'd have to calculate something.

Formula i used was just V=IR
$V = (1200 A)(1.0\times10^{-5} \Omega)(3.0\times10^{-1}m)= 3.6 \times 10^{-3} V$

That's what i got as a final answer

For question two, our books didn't really mention anything about formulas with the tesla unit so i guess we had to research it.

I found a formula that was :

$B=\frac {F} {IL} \vspace$

B is 1.10T
I is 2.50 A
L i think would be 1m since they wanted the force per metre.
F is the unkown

So in the end i got $F = BI<br /> <br /> = 1.10T \times 2.50A =2.75 N/m$

Just need some feedback on those questions.

 

[vincentchan]

good job
i didn't check your number, but you have applied the formulas correctly

 

[wais]

Great job on your work for these two questions! Your approach and use of the appropriate formulas are correct. For question one, you are correct in thinking that the bird should not feel any voltage since it is not grounded. However, the question is asking for the voltage that the bird feels, not the voltage on the line. So, your calculation of 3.6 x 10^-3 V is correct.

For question two, you have correctly researched and used the formula for the magnetic field. Your calculation of 2.75 N/m is also correct. Just make sure to pay attention to units - in this case, the magnetic field strength should be in Tesla (T) and the current should be in Amperes (A).

Overall, great job on these questions! Keep up the good work on your ISU.