Formula for the strength of an electromagnet

[Mindstormed]

Trying to determine the strength of an electromagnet in Teslas, with an iron core.
Some sites have the same basic formula but with different units after B=

Some use μ0, μr, or μ. Which one to use?

For N (the number of turns), is this the general number of turns accounting for multiple layers, or turns per meter (or inches), or what?

And L (the length), is it the length of the iron core or the length of the wire used, and should it be in meters or inches?

According to this site (http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/solenoid.html), a 0.1 meter (4") length solenoid (I'm assuming their talking about the iron core?) with 200 turns, 1 amp, and an iron core with 200 relative permeability is 0.5 Tesla. With 3 amps, this is about 1.5 Tesla and that doesn't sound right.

Any help is appreciated, thanks!

 

[mgb_phys]

Some use μ0, μr, or μ. Which one to use?

μ = μ0 * μr
μ0 is a fundamental constant, you also need μr for your core material, or the book may just list μ and do the multiplication for you.

For N (the number of turns), is this the general number of turns accounting for multiple layers, or turns per meter (or inches), or what?

Just the total number of turns.

And L (the length), is it the length of the iron core or the length of the wire used, and should it be in meters or inches?

It's the length of the core that has coils wrapped around it.

You can use any units you like, as long as you have matching units for μ.
It's probably safest to use metres for everything.

a 0.1 meter (4") length solenoid (I'm assuming their talking about the iron core?) with 200 turns, 1 amp, and an iron core with 200 relative permeability is 0.5 Tesla. With 3 amps, this is about 1.5 Tesla and that doesn't sound right.

Nope that sounds a bit high.


μr iron = 5000 μr steel = 200 (varies a lot!)
B = μ N I / h = 200 * 4pi*10^-7 * 200 * 1 / 0.1 = 0.5T
which still sound s a lot - but this is the field inside the core - the field outside the coil is much lower.

 

[astrokreng]

I would like to clarify and provide some insights on the formula for the strength of an electromagnet. First of all, the formula for the strength of an electromagnet is given by B = μ0 * μr * (N/L) * I, where B is the magnetic field strength in Teslas, μ0 is the permeability of free space (4π * 10^-7 T*m/A), μr is the relative permeability of the material (in this case, iron), N is the number of turns, L is the length of the core, and I is the current flowing through the wire.

To address the question of which unit to use after B, it is important to note that Teslas is the standard unit for magnetic field strength. However, some sources may use different units such as Gauss or Maxwell, which can be converted to Teslas using appropriate conversion factors.

Regarding the use of μ0, μr, and μ, it is important to understand that these are all related to the permeability of the material. μ0 is the permeability of free space, μr is the relative permeability of the material, and μ is the absolute permeability of the material. In the formula, μ0 * μr is often used as a combined value for simplicity, but you can also use μ instead.

Moving on to the question about N, it is important to specify whether N refers to the total number of turns or the turns per unit length. In most cases, N refers to the total number of turns in the coil. However, if the coil has multiple layers, then the total number of turns would be the product of the number of turns per layer and the number of layers. It is important to be consistent with the units used for N and L, whether it is in meters or inches.

Lastly, for L, it refers to the length of the core, not the length of the wire used. This is because the magnetic field is mainly concentrated within the core, and the length of the core is what determines the strength of the magnetic field.

To address the concern about the calculation on the website, it is possible that there may be some discrepancies in the values used for μr or the dimensions of the solenoid. It is always recommended to double-check the values and units used in the formula to ensure accurate results.

In conclusion, the formula for the strength of an electromagnet can be used to calculate the