Bar Magnet

The lines of magnetic field from a bar magnetform closed lines.By convention, thefield direction istaken to be outward from theNorth pole and into the South poleof the magnet. Permanent magnets can be made from ferromagnetic materials.

Comparison of magnetic and electric fieldsCompare to solenoid magnetic field
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Electric and Magnetic Sources

The electric field of a point charge is radially outward from a positive charge.The magnetic field of a bar magnet.
Electric sources are inherently "monopole" or point charge sources.Magnetic sources are inherently dipole sources - you can't isolate North or South "monopoles".
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Magnetic force

Magnetic field concepts
 
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Bar Magnet and Solenoid

The magnetic field produced by electric current in a solenoid coil is similar to that of a bar magnet.

Add iron core to solenoid
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Magnetic field concepts
 
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Iron Core Solenoid

An iron corehas theeffect of multiplying greatly the magnetic field ofa solenoid compared to the air core solenoid on the left.

Properties of iron core solenoid
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Magnetic field concepts
 
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Electromagnet

Electromagnets are usually in the form of iron core solenoids. The ferromagnetic property of the iron core causes the internal magnetic domains of the iron to line up with the smaller driving magnetic field produced by the current in the solenoid. The effect is the multiplication of the magnetic field by factors of tens to even thousands. The solenoid field relationship is

and k is the relative permeability of the iron, shows the magnifying effect of the iron core.

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Magnetic field concepts
 
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