What area does the flux formula refer to?

In summary, the conversation discusses the concept of electromagnetic induction and the different approaches used to explain it. The first approach involves a metal rod moving through a magnetic field and cutting through the field lines at a constant speed, while the second approach involves moving a bar magnet through a coil. In the latter, the area used in the formula refers to the cross section of the coil, which may seem counterintuitive as only a small area of the wire is actually cutting through the magnetic field. This is because in the case of a coil, there is interest in the magnetic-flux through the entire coil, rather than just the area swept out by the wire.
  • #1
koliko987
6
0
I've been studying em induction and in my book it was explained by considering a metal rod of length l moving through a magnetic field and cutting through the field lines at a constant speed. So in time dt it moves through ds and they showed e=BA/dt, where A = l x ds(the area that the rod "sweeps out".
Then in the next chapter it explains induction when moving a bar magnet through a coil and this time the "A" in the formula referred to the area of the cross section of the coil (the circle area of one of the rings of the wound up wire). Why is this? The magnetic field lines are only cutting through the small area of the wire, the rest of the "circle" is empty space so why are we considering the whole area of the cross section. What's different now that we're not looking for area that the wire "sweeps out"?
Thank you for your help
 
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  • #2
You can study any surface you want.

I presume that this coil is not part of a circuit with a source.
In the case of a coil, there is interest in the magnetic-flux through the coil (that is, an area where the coil marks the boundary of that area). That flux will be related to the electric-field induced along that boundary.
 

Related to What area does the flux formula refer to?

1. What is the flux formula used for?

The flux formula is used to calculate the flow of a physical quantity through a defined surface or area. It is commonly used in fields such as physics, engineering, and mathematics to understand and analyze how certain quantities, such as heat or electric fields, behave in a given space.

2. How is the flux formula calculated?

The flux formula is calculated by multiplying the magnitude of the physical quantity by the area of the surface it is passing through and the cosine of the angle between the surface and the direction of the flow. This formula is represented as Φ = A * B * cos(θ), where Φ is the flux, A is the magnitude of the quantity, B is the area, and θ is the angle between them.

3. What does the area in the flux formula refer to?

The area in the flux formula refers to the surface or cross-sectional area through which the physical quantity is passing. This can be a flat surface, a curved surface, or any defined area that is perpendicular to the direction of the flow.

4. What are some real-life applications of the flux formula?

The flux formula has various real-life applications, such as calculating the flow of heat through a building, the flow of electric current through a wire, and the flow of fluid through a pipe or channel. It is also used in meteorology to understand the movement of air and in environmental sciences to study the transport of pollutants in water bodies.

5. Are there any limitations to the flux formula?

While the flux formula is a useful tool for understanding the flow of physical quantities, it does have some limitations. It assumes that the physical quantity is evenly distributed over the surface and that the surface is flat or has a constant curvature. It also does not take into account any changes in the direction or magnitude of the flow, which may affect the accuracy of the calculations.

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