|Mar14-12, 09:44 PM||#1|
Magnetic Force in a Current Carrying Wire
1. The problem statement, all variables and given/known data
The current in a wire consists of n electrons per unit volume moving with a velocity v. What is the effect on these electrons of the magnetic field set up by the current itself within the wire? What is the force on one electron at a distance r from the centre of the wire?
2. Relevant equations
F = QvBsinθ
Magnetic field strength at a distance r from the axis of the wire outside the wire = u0I/2∏r
3. The attempt at a solution
I know that for part 1, the effect of the magnetic field on the electrons inside the wire will be a radially outward force (taking all electrons to be travelling in straight lines along the wire).
F will be equal to QvBsin90 = QvB
Making the subsitution for B I have
F = Qvu0I/2∏r
I believe now that I have to make subsitution for I. Which would be 4/3∏a3vne
where e is fundamental charge and a is the radius of the wire.
F = (3/8)u0ve2na3r
I know that the answer is:
F = (1/2)u0v2e2nr
I think I'm making a mistake in calculating my current, but I'm not sure. Help Please?
|Mar15-12, 12:14 AM||#2|
Hi! This is my first time helping someone out so here goes:
To make the substitution for current I, you should use:
[itex] I=\int J \bullet da [/itex]
where J is the current density, equal to nev in this case. After doing a quick integration you should get the proper current which will give the correct answer for the force.
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