What is the current in the hanging wires?

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Homework Help Overview

The problem involves two parallel wires hanging at an angle, with a focus on determining the current they carry based on their weight and the forces acting on them. The context includes concepts from electromagnetism and forces in physics.

Discussion Character

  • Exploratory, Conceptual clarification, Mathematical reasoning, Problem interpretation

Approaches and Questions Raised

  • Participants discuss the relevant equations, including the force due to current and magnetic fields. There is an exploration of how to calculate the magnetic field and the forces acting on the wires. Questions arise about the definitions of variables and the interpretation of the problem setup.

Discussion Status

The discussion is active, with participants providing insights into the equations involved and clarifying the meanings of variables. Some participants have suggested drawing diagrams to visualize the forces, while others are considering the implications of treating the wires as infinite. There is no explicit consensus yet, but guidance on approaching the problem has been offered.

Contextual Notes

Participants note potential confusion regarding the length of the wires and the assumptions about their configuration. The weight of the wires and the angle at which they hang are also central to the discussion.

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Homework Statement


In the figure, two wires are hanging parallel to one another. Each wire hangs 7 degrees from the vertical on 5 cm long cords. If the wires weigh 35 grams per meter, how much current do they carry?
http://www.usi.edu/science/physics/pickett/206/15p2f1.jpg
Also, the current is going opposite directions.

Homework Equations


Maybe,
F=i*L*B


The Attempt at a Solution


I don't know what equations work here. I know I need to find the force on each wire which pushes them apart, but how do I go about doing that?
 
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I presume ## i ## is the current. What are ## L ## and ## B ##?
 
L is the length of the wire and B is the magnetic field
 
Draw a picture of the wires end-on and draw in the forces acting on the wires each of length L. Include the suspension wires and dimensions.
 
Colts said:
L is the length of the wire and B is the magnetic field

Very well, you have the basics right. Do as rude man suggests, and find out B felt by one as a result of the current in another wire, that will give you the force.
 
I messed up. I read the problem as the wire is 5 cm long, but I think we treat this as the wire is infinite and the cords holding the wire is 5 cm long. So now I can use
B=(μ*i)/(2∏*D) where D is the distance from the wire and μ is the magnetic constant in equations.
Also, this is the equation for magnetic force from an infinite wire. We derived this in class.

Now how do I get B from this?

Can I still use the F=i*L*B and chose an arbitrary length of the wire and set that force equalt to the force f gravity acting on that piece?
Which will give me B and in turn i?
 
Yes, you can choose an arbitrary length of wire. Note that wire's density per length is given, so both the force and the mass will depend on this length, and it will cancel out.
 

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