- #1
shirobon
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Homework Statement
Given the figure below[/B]
I need to calculate the total magnetic force on the semicircle section of the conductor.
Current is I, Radius is R, and the Magnetic Field is B.
Homework Equations
[tex]d\vec{F} = Id\vec{l} \times \vec{B}[/tex][/B]
The Attempt at a Solution
[/B]
[itex]dl [/itex] is equal to [itex]Rdθ[/itex]
Since [itex]d\vec{l}[/itex] and [itex]\vec{B}[/itex] are perpendicular, the magnitude of the force on the segment [itex]d\vec{l}[/itex] is equal to [itex]I dl B = I(Rdθ)B[/itex], and the components of these forces is [itex]I(Rdθ)Bcosθ[/itex] and [itex]I(Rdθ)Bsinθ[/itex]. Integrating these separately from 0 to π and adding the result gives [itex]IB(2R+L)j[/itex].
However, I am trying to solve it using the cross product to obtain [itex]d\vec{F}[/itex] and then solve it from there.
The magnetic field vector is [tex]0i + 0j + Bk[/tex]
And the vector for [itex]d\vec{l}[/itex] I got was [tex]Rdθcosθ i + Rdθsinθ j + 0k[/tex]
Calculating the cross product yields
[tex]-IBRdθsinθi + IBRdθcosθj + 0k[/tex]
Integrating to from 0 to π to obtain [itex]\vec{F}[/itex] yields
[tex]-2IBRi + IBRj + 0k[/tex]
This vector is obviously different than what was obtained before, and I am wondering where I went wrong.
I think that a place I could have gone wrong is when I found [itex]d\vec{l}[/itex] as [tex]Rdθcosθ i + Rdθsinθ j + 0k[/tex], but I don't know of any other way I could get the components for the vector.
I'd appreciate if somebody could enlighten me as to where I went wrong. Thank you.