Calculating magnetic field strength (complex)

In summary, the conversation was about the difficulty in measuring the magnetic field strength of a magnet in an experiment involving eddy currents. The group discussed using an online calculator and the Zeeman effect as possible solutions, but acknowledged the complexity of the subject. One member mentioned that astronomers use a similar method to measure the magnetic field strength of stars.
  • #1
Ghengis
7
1
okay guys, i think I am out of my depth on this problem.

Im doing a long investigation on eddy currents, and i derived a formula. I am reaching the end of the investigation, and so i wanted to compare my experimental data to expected data. One of the factors i was investigating is the relationship between the terminal velocity of a magnet and its magnetic field strength in the scenario where a magnet is dropped down a copper tube.

However, as the magnet was too strong for my magnetic field measuring probe to measure, i measured it at 1 cm away from the magnet.
Is there any equation that can determine the actual magnetic field strength of a magnet, from the magnetic field strength of a magnet at 1 cm away.

Also, just as a side note, is there any way to determine the height of eddy currents algebraically. I know that the height of the eddy currents is the cross sectional area of the eddy currents divided by the thickness of the conductor. (ie h=A/z), but how do you determine the cross sectional area of the eddy currents.

Thanks so much!
 
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  • #2
Um, guys, i really need your help :)
 
  • #3
This is a point most textbooks don't even touch.

I've once read that if you have a small magnetic dipole, the field will follow an inverse-square law. But I'm not sure.

About calculating eddy currents, you would need more details such as how the magnetic field is distributed - and this will probably be complicated. Remember that even for the simplest cases (spire, solenoid...), the equations are only approximations.

I really wish I could help you more, but I'm not an expert in this subject.
 
  • #4
Ghengis said:
Is there any equation that can determine the actual magnetic field strength of a magnet, from the magnetic field strength of a magnet at 1 cm away.
Here is an on-line magnetic field and force calculator that may help. There are also other on-line calculators on the web if this is unsatisfactory.

http://www.kjmagnetics.com/calculator.asp

Bob S
 
  • #5
You probably won't be able to do this , but ill tell you so can learn what it is .
you could put your magnet near a gas discharge tube of let's say neon , and the magnetic field will alter the electrons orbital a little bit and cause a shift in the spectral lines
and the energy shift in the light would be the field strength multiplied by the bohr magneton , this is called the zeeman effect . and you would haft to measure the wavelength of the light .
and your bar magnet might not be strong enough to get any size-able shift .
 
  • #6
@cragar:

Despite the practical problems (such as cost), this is the first time I've heard Zeeman effect could be used backwards.

Really cool!
 
  • #7
I think this is how astronomers measure the B field strength of stars , by looking at the shift in the light .
 

1. What is the formula for calculating magnetic field strength?

The formula for calculating magnetic field strength is B = μ0 * (N * I) / L, where B is the magnetic field strength, μ0 is the permeability of free space, N is the number of turns in the coil, I is the current flowing through the coil, and L is the length of the coil.

2. How do you calculate the direction of the magnetic field?

The direction of the magnetic field is perpendicular to the direction of the current flow and follows the right-hand rule. This means that if you point your right thumb in the direction of the current flow, your fingers will curl in the direction of the magnetic field.

3. What is the unit of measurement for magnetic field strength?

The unit of measurement for magnetic field strength is Tesla (T) in the SI system. However, it is often expressed in smaller units such as milliTesla (mT) or microTesla (μT).

4. How does the number of turns in a coil affect the magnetic field strength?

The number of turns in a coil is directly proportional to the magnetic field strength. This means that as the number of turns increases, the magnetic field strength also increases. This relationship follows the formula B ∝ N * I, where B is the magnetic field strength and N is the number of turns.

5. Can magnetic field strength be negative?

No, magnetic field strength cannot be negative. It is a vector quantity, meaning it has both magnitude and direction, but it cannot have a negative magnitude. The negative sign may appear in equations to indicate the direction of the magnetic field, but the actual value of the field strength is always positive.

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