Electromagnet with and without airgap.

In summary, the physical explanation for the difference in fieldstrength between electromagnets with and without airgaps is that the airgap creates a magnetic resistance which reduces the magnetic flux density in the core of the electromagnet.
  • #1
center o bass
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Hello! I'm a bit confused by a phenomenon regarding electromagnets with and without airgaps.

A picture of the kind of electromagnet i have in mind is found here:

http://sci-toys.com/scitoys/scitoys/magnets/calculating/calculating.html

If one has a "loopy" electromagnet without an airgap, the effect of the material will be to boost the magnetic field strength by a certain factor and guide the fieldlines trough the material. This is because the initial field will tend to align the magnetic dipoles inside the material which in turn will create a bigger "current" inside the material.. the current being the source of the magnetic field.

But if one now introduces a little tiny airgap the fieldstrength goes down dramatically.

In the picture of magnetic dipoles, induced volumecurrents and surface currents, what is the physical explanation of this?
 
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  • #2
center o bass said:
... if one now introduces a little tiny airgap the fieldstrength goes down dramatically...what is the physical explanation of this?

The easy answer:

By analogy with an electrical circuit.. If you connect a voltage source to a short-circuit then a large electric current flows. If you then introduce a small resistance in the circuit the electrical current goes down dramatically.
The iron core of a toroidal (donut with a hole) electromagnet is equivalent to a magnetic "short circuit". The tiny airgap is equivalent to a magnetic resistance ("magnetic reluctance" is the correct term for this.)

The hard answer:

To fully, and correctly, explain what is going on in the air gap and in the iron core we need to use the two separate concepts of Magnetic Flux Density "B" and Magnetic Field Strength "H". Inside and outside the core those two quantities behave in different ways. Explaining the theory needs far more space than available here. The Wikipedia article "Magnetic Field" will get you started.
 

FAQ: Electromagnet with and without airgap.

What is an electromagnet?

An electromagnet is a type of magnet that is created by passing an electric current through a coil of wire. The wire is wrapped around a metal core, such as iron, and the electricity creates a magnetic field, making the core magnetic.

What is an airgap in an electromagnet?

An airgap is a space between the metal core and the wire in an electromagnet. This space is important because it allows the magnetic field to be stronger by preventing the metal core from becoming fully magnetized, which would weaken the overall magnetic field.

How does an electromagnet with an airgap differ from one without an airgap?

An electromagnet with an airgap has a stronger magnetic field than one without an airgap. This is because the airgap prevents the metal core from becoming fully magnetized, allowing the magnetic field to focus on a smaller area and become stronger.

What are some applications of electromagnets with and without airgaps?

Electromagnets with airgaps are commonly used in electric motors, generators, and speakers, where a strong magnetic field is needed. Electromagnets without airgaps are often used in particle accelerators and MRI machines, where a uniform and precise magnetic field is necessary.

How can the strength of an electromagnet with an airgap be increased?

The strength of an electromagnet with an airgap can be increased by increasing the number of turns in the wire coil, increasing the amount of current flowing through the wire, or by using a stronger metal core. Additionally, reducing the size of the airgap can also increase the strength of the magnetic field.

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