Effect of Ferrous Cores and the Relationship between Current and Field Strength

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Effect of Ferrous Cores and the Relationship between Current and Field Strength

Electromagnets all consists of a current carrying conductor, however the strength of the magnetic field produced also depends on the surrounding substance. Air is not particularly good at 'carrying' a magnetic field and so the field around a wire is quite weak. By placing a core inside of a coil the strength of the magnetic field can be increased.

By putting a ferrous (iron) core inside a solenoid, the field lines are concentrated. This has the effect of strengthening the field.

Diagram

Inside the core, the field lines are much closer together → stronger field.

Iron is a particularly good core for solenoids as it is easily magnetised and demagnetised. This means that when the current is switched off the iron does not stay magnetic. Iron is said to be magnetically soft.

Steel increases the strength of the field, however, it is not as effective as iron and does not lose its magnetism as quickly when the current is switched off. Steel is said to be magnetically hard.

The strength of a magnetic field is directly proportional to the current flowing.

B ∝ I

Therefore, if an alternating current is flowing, a magnetic field around the conductor will be produced, that is in phase with the alternating current.

Diagram

The graphs show that the magnetic field is created due to the movement of charged particles.

When you have the greatest movement of charged particles, for instance - the maximum current is flowing, you have the greatest induced magnetic field.

The two graphs are in phase.

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