A magnetic field between two long poles will look like this:
If we place a non magnetic material in between the poles it will not change the shape of the magnetic field:
non magnetic material placed between poles of a magnet
If we place magnetically soft iron in between the poles it will change the shape of the magnetic field:
soft iron (magnetic material) placed between poles of a magnet
Soft iron in a magnetic field will easily be induced thus many field lines will move closer to the iron object. This happens because the iron has become an induced magnet itself.
| Example 1 |
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| A piece of soft iron placed between two magnetic poles becomes an induced magnet.
What are the poles on the top and the bottom of the piece of iron?
As can be seen the top face becomes a south pole and the bottom face becomes a north pole. |
| Direction of Field Lines Inside a Magnetic Material |
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| Looking at the above example a bit more closely and we will realise that whilst the field lines do go towards the south pole and away from the north pole when outside the iron they actually travel the other way when inside the soft iron.
Magnetic field fines go from south to north when inside a magnetic material. |
Magnetic Screening (Shielding)
Magnetic field lines cannot be destroyed or absorbed but they may be channelled away to protect specific region; materials which do this are themselves magnetic. This is known as magnetic screening or magnetic shielding.
The soft iron ring above seems to attract the field lines toward it and channel them away from the central area. It has the effect of shielding the central area from the magnetic field.
Looking closer at the soft iron shield and we can see that the field lines actually pass through it.
| Example 2 |
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| Complete the diagram to show the shape of the magnetic field around a bar magnet placed next to an iron sheet.
The field will look like this:
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| Magnetism Notes 17.5 – (Mr Shone Explains) |