# Calculating flux with a magnet and a coil

## Homework Statement

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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

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

## The Attempt at a Solution

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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?

Anne

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kuruman
Homework Helper
Gold Member
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.

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.

kuruman