- #1
Flux from magnet (Why is the Flux not zero through the loop?)
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SUMMARY
The discussion centers on the calculation of magnetic flux through a loop in the presence of a magnetic field. Participants clarify that the magnetic flux is not zero due to the nature of the surface being open, and they reference the equation for magnetic flux, which is given by ##\phi = BA\cos\theta##. The sign of cosθ is critical, as it determines the direction of the magnetic field relative to the surface normal. Ultimately, the conclusion is that the magnetic flux is negative because the angle θ is greater than 90 degrees, resulting in ##\cos\theta < 0##.
PREREQUISITES- Understanding of magnetic flux and its definition
- Familiarity with the equation for magnetic flux: ##\phi = BA\cos\theta##
- Knowledge of surface normals in relation to magnetic fields
- Basic principles of electromagnetism
- Study the implications of surface orientation on magnetic flux calculations
- Explore the concept of open versus closed surfaces in electromagnetism
- Learn about the significance of the angle θ in magnetic field interactions
- Investigate applications of magnetic flux in real-world scenarios, such as electromagnetic induction
Students and professionals in physics, particularly those studying electromagnetism, as well as educators looking to clarify concepts related to magnetic flux and field interactions.
- #2
Frabjous
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Here‘s a picture of the field lines. Why do you think the answer is zero?
- #3
member 731016
Thanks for your reply @Frabjous! because the number of field lines going into the loop is equal to the number going out.Frabjous said:
- #4
nasu
Homework Helper
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This is an open surface. There is no in and out. These apply only to closed surfaces. You should review the definition of flux through a surface. According to your idea, the flux would be always zero.
- #5
Frabjous
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The flux is a measure of the net amount going through a surface. What equation are you using for flux?
- #6
- #7
Frabjous
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What is the sign of cosθ for the surface of interest? Hint: the normal to the surface is pointing to the right. The B field is pointing to the left.
Last edited:
- #8
member 731016
Thanks for your reply @Frabjous ! I think the direction of the B-field relative to the surface normal varies along the surface.Frabjous said:
Many thanks!
- #9
Frabjous
Gold Member
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Yes it varies, but it is all the same sign. What is the sign?
- #10
member 731016
Thanks for your reply @Frabjous ! I think the sign is negative because ##\theta > 90 ## so ##\cos\theta < 0 ##Frabjous said:
Thanks again, I see why the magnetic flux is negative now.
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