Finding the Magnetic force on the coil

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Homework Help Overview

The discussion revolves around calculating the magnetic force on a coil, specifically focusing on the integration of forces acting on the coil due to a magnetic field. The subject area includes concepts from electromagnetism and circular motion.

Discussion Character

  • Exploratory, Assumption checking, Mathematical reasoning

Approaches and Questions Raised

  • The original poster attempts to resolve the magnetic force into components and integrate over the full circular path of the coil. Some participants question the correctness of the force direction and the implications of integrating over the entire circle.

Discussion Status

Participants are actively engaging with the original poster's approach, providing feedback on the direction of forces and the setup of integrals. There is a mix of validation and questioning, with some guidance offered regarding the integration process and the cancellation of components.

Contextual Notes

There are indications of potential misunderstandings regarding the direction of current and the resultant forces, as well as the need to consider the number of turns in the coil during calculations.

Physicslearner500039
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Homework Statement
A voice coil in a loudspeaker has 50 turns of wire and a diameter of 1.56 cm, and the current in the coil is 0.950 A. Assume that the magnetic field at each point of the coil has a constant magnitude of 0.220 T and is directed at an angle of 60.0 Deg outward from the normal to the plane of the coil. Let the axis of the coil be in the y-direction. The current in the coil is in the direction shown (counterclockwise as viewed from a point above the coil on the y-axis). Calculate the magnitude and direction of the net magnetic force on the coil.
Relevant Equations
F=ILBSin(Θ)
1598025773773.png

Surely a tough one, I am doing it from the basics. This is the diagram i tried to draw showing the Force and current I
1598027435817.png


The Length L is the tangent to the circle. The Force F is pointing upwards at ##90 Deg## to the ##\vec B## and also perpendicular to ##\vec L##. I am considering a small length ##\vec dL = r d\theta##. Resolving the force into X and Y components and integrating over the complete ##2\pi##.

##Fx = \int_0^{2\pi} IRB\sin(30) d\theta ##
##Fy = \int_0^{2\pi} IRB\cos(30)d\theta ##

Is my approach correct or completely wrong? Please advise
 
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Check the direction of F in your drawing. The current is going into the page at the point where you draw F.

If you consider the forces on diametrically opposite elements of current, what happens when you add their horizontal components?

Your integral for ##F_y## looks good except for maybe the overall sign. If ##\theta## varies from 0 to ##2 \pi##, how many times do you go around the cylinder?
 
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TSny said:
Check the direction of F in your drawing. The current is going into the page at the point where you draw F.
I am not sure how i have done that mistake, the updated diagram is
1598076875045.png

The horizontal components cancel out. The vertical component is for N turns
##-\int_0^{2\pi} NIRB\cos(30)d\theta##
##-\pi NIRB\sqrt3 = -0.443 \hat j N##
 
Looks right to me.
 
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