Calculating flux with a magnet and a coil

In summary, the student is having difficulties with their physics project which involves calculating the magnetic field using the formula U = -N • d Φ / dt. They are using a setup with a magnet falling through a PVC tube with a coil around it connected to a voltage probe and LoggerPro. The student knows the number of windings (N) and LoggerPro provides the time (t) and induction voltage (U). They need to calculate the flux (Φ) using a diagram, but are unsure of how to do this due to the "d" in the formula. The expert suggests using the formula Φ = ∫(U(t)/N)dt to find the total flux, and explains that this involves finding the area
  • #1
AnneClara
3
0

Homework Statement


[/B]
Hey, I'm having some difficulties with my physics project and I hoped someone could help me out. We have to calculate the magnetic field, but first we need to know the flux.

This is the setup we got:
We have to let a magnet fall through a PVC tube. The tube has a coil around it (it covers just a small part of the tube) which is connected to a voltage probe. The voltage probe is connected to a laptop with LoggerPro.

Then we have to calculate the flux ( Φ ) with the results we got in LoggerPro.

Homework Equations


[/B]
I already know that I have to use the formula U = -N • d Φ / dt
(d, not Δ!)

The Attempt at a Solution


[/B]
I do know how many windings the coil has (N) and LoggerPro shows the time (t) and the induction voltage (U). The flux has to be calculated with a diagram.
But I don't really know how to do this due to the 'd' in the formula. I've been told that I have to do something with the derivative and the surface in the diagram, but I'm not sure how to do this.

Does anyone have an idea how to do this?
Thanks in Advance!

Anne
 
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  • #2
I assume that LoggerPro has given you U(t) as a function of time. Note that you can write dΦ/dt=(U(t)/N). (The minus sign is irrelevant here.) Then the total flux is Φ = ∫(dΦ/dt)dt = ∫(U(t)/N)dt. Got it?

Welcome to PF, AnneClara.
 
  • #3
kuruman said:
I assume that LoggerPro has given you U(t) as a function of time. Note that you can write dΦ/dt=(U(t)/N). (The minus sign is irrelevant here.) Then the total flux is Φ = ∫(dΦ/dt)dt = ∫(U(t)/N)dt. Got it?

Thank you!
LoggerPro gives the U as a function of the t indeed. But I don't really know how to put this in a graph to get the flux.
 
  • #4
You don't really need a graph to get the flux. Look at what ∫(U(t)/N)dt, which is equal to the flux, is saying you should do.
∫ means "add", add what? Answer: the ratio U(t)/N at a given time t (provided by LoggerPro in a table) multiplied by dt. OK, so what's dt? Answer: the constant time interval between measurements (also provided by LoggerPro). In other words, you want the area under the curve, not the curve itself. You approximate this area by the sum of areas of rectangles of height U(t)/N and width dt. If you don't know how to (or can't) do this directly in LoggerPro, I suggest that you export the file to spreadsheet format which you can then process as you please.
 
  • #5
kuruman said:
You don't really need a graph to get the flux. Look at what ∫(U(t)/N)dt, which is equal to the flux, is saying you should do.
∫ means "add", add what? Answer: the ratio U(t)/N at a given time t (provided by LoggerPro in a table) multiplied by dt. OK, so what's dt? Answer: the constant time interval between measurements (also provided by LoggerPro). In other words, you want the area under the curve, not the curve itself. You approximate this area by the sum of areas of rectangles of height U(t)/N and width dt. If you don't know how to (or can't) do this directly in LoggerPro, I suggest that you export the file to spreadsheet format which you can then process as you please.

Thank you so much! :)
 

1. How do you calculate the flux of a magnet and a coil?

To calculate the flux of a magnet and a coil, you can use the formula F = B * A * cos(theta), where F is the flux, B is the magnetic field strength, A is the area of the coil, and theta is the angle between the magnetic field and the normal to the coil's surface.

2. What is the relationship between flux and the strength of a magnet?

The flux is directly proportional to the strength of a magnet. This means that the stronger the magnet, the higher the flux will be.

3. Can the distance between the magnet and coil affect the flux?

Yes, the distance between the magnet and coil can affect the flux. As the distance increases, the flux decreases. This is because the magnetic field weakens as it spreads out over a larger area.

4. How does the number of turns in a coil affect the flux?

The number of turns in a coil does not directly affect the flux. However, it can indirectly affect the flux by increasing the coil's surface area, which can result in a higher flux if the magnetic field strength remains constant.

5. What is the unit of measurement for flux?

The unit of measurement for flux is weber (Wb) in the SI system. It can also be measured in gauss (G) or tesla (T), with 1 T = 10,000 G.

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