Calculating the magnetic flux

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IvyYang
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Joined: Thu Apr 22, 2021 2:29 am
Occupation: Teacher

Calculating the magnetic flux

Post by IvyYang »

Hi, I am doing the experiment posted on this website called High Speed Magnets: Exploring Faraday's and Lenz's Laws. More specifically, I am doing the experiment on how the rate of change of the magnetic flux affects the voltage of electricity induced in the coil (Faraday's law). The rate of change of the magnetic flux will be made different by dropping the magnet through the coil at different heights. From that, I will know the different velocities of the magnet as well as the time taken for it to travel through the coil. So, I was wondering whether I will be able to calculate the magnetic flux/change of the magnetic flux from that? If so, how do I calculate it?


Moderator note: Hi Ivy, I removed your second post. It was in Grades 6-8. Let us know if you wanted to keep that one and remove this one, in Grades 9-12! Thanks!

(Project reference: https://www.sciencebuddies.org/science- ... -lenzs-law)
bfinio
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Re: Calculating the magnetic flux

Post by bfinio »

Hi Ivy,

Sorry for the delay in replying to your post. If you look at the Hyperphysics page linked in the bibliography of the project:

http://hyperphysics.phy-astr.gsu.edu/hb ... arlaw.html

It links to a page with the formula for magnetic flux:

http://hyperphysics.phy-astr.gsu.edu/hb ... mg.html#c1

However, in practice, this is very difficult to calculate because you do not know the value magnetic field strength B at every point in space around the magnet. If you purchase magnets from a specialty supplier sometimes they will list the magnetic field strength at the *surface* of the magnet, for example: https://www.kjmagnetics.com/proddetail.asp?prod=D11SH

But that doesn't help you when, for example, the magnet is falling towards the solenoid and is still 1cm away. You don't know B 1cm from the surface of the magnet. In theory, if you really wanted to do that, there are a few options to take your own measurements for the magnetic field at varying distances from the magnet:

1. Buy a Gauss meter (search on Amazon)
2. Download a magnetometer app on your phone, or a more general physics app like Phyphox that gives access to the magnetometer data. This is difficult though because you don't know exactly where the magnetometer is located inside your phone
3. Build your own circuit to measure magnetic fields with a Hall effect sensor, which you can see in this Science Buddies project: https://www.sciencebuddies.org/science- ... tic-fields

However, you could also just demonstrate the relationships between the different variables in the equations, without calculating their exact values. e.g. from Faraday's Law you can see that the voltage is proportional to the rate of change of magnetic flux, and you can verify this relationship by collecting data, even if you don't have the exact values/units correct for the two different variables (e.g. you assume rate of change of magnetic flux is proportional to the velocity of the magnet as you mentioned).

Hope that helps!

Ben
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