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ichivictus
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Homework Statement
A telegraph consisted of 2 long straight wires carrying currents equal in magnitude but oppositely directed. Each was suspended by a pair of light-weight and inelastic threads that were about 6cm long. When current flowed through the wires, the magnetic force exerted between them caused them to move apart.
Given that the linear mass density of the wire is 40 g/m, find the magnitude of the current in either wire when the angle separating the threads of the device is 16 degrees.
Homework Equations
Here's a pic of the object: http://i.imgur.com/zwZLzPX.png
F = qv x B = qvBsin(theta)
B = U/2∏ * I/R (Due to a long straight wire) (U is the permeability of empty space.)
The Attempt at a Solution
I tried solving for B from the first equation then plugging it into the 2nd then solving for I.
I = FR2pi/qvsin(theta)
But I'm pretty much stuck. I think I'm missing something really simple but not sure. I know I'm going to need to write an expression of the mag field due to the current in a long straight wire and force on a long straight wire carrying some current though.
Any hints would be great :)