Magnetic flux density: The strength and effect of a magnetic field

The magnetic flux density, also known as magnetic induction, describes the strength of a magnetic field at a specific point and its effect on charged particles or magnetic materials. It is measured in the unit Tesla (T) and is a vector quantity that has both magnitude and direction.

What is magnetic flux density?

Magnetic flux density describes how dense the magnetic field lines are in a certain area. The denser the field lines, the greater the flux density and therefore the magnetic effect. It is a measure of the magnetisation of a material or the strength of a magnetic field.

Formula for magnetic flux density

Magnetic flux density is defined as the magnetic flux ( Phi ) per area ( A ) through which the magnetic field runs perpendicularly:

B = Φ / A

Where:

• ( B ): Magnetic flux density (in Tesla, T)
• ( Phi ): Magnetic flux (in Weber, Wb)
• ( A ): Area through which the magnetic field passes (in square metres, m²)

Relationship with the magnetic field strength

The magnetic flux density ( B ) is directly related to the magnetic field strength ( H ) and the permeability ( μ ) of the material:

B = μ - H

Whereby the permeability ( μ ) describes how strongly a material reacts to a magnetic field. In air-free or vacuum-free environments, ( μ ) is given by the magnetic permeability of the vacuum ( μ₀ ), which has a constant value.

Properties of the magnetic flux density

• Vectorial quantity: The magnetic flux density has a direction and a magnitude.
• Field lines: It is proportional to the density of the magnetic field lines that run from the north to the south pole of a magnet.
• Material-dependent: The flux density is influenced by the magnetic permeability of the material.

Applications of magnetic flux density

Magnetic flux density is of central importance in many technical and scientific applications:

• Electric motors and generators: Magnetic flux density is crucial for the conversion of electrical and mechanical energy.It also determines the magnetic force of electromagnets and therefore their possible applications in industry, science and technology.
• Magnetic resonance imaging (MRI): In medical technology, strong magnetic fields with high flux density are used to generate high-resolution images of the body.
• Transformers: The flux density determines the efficiency of energy transfer between coils.
• Magnetic shielding: High flux density materials are used to protect sensitive devices from external magnetic fields.

Magnetic flux density in nature

Magnetic flux densities also occur in nature:

• Earth's magnetic field: The flux density of the Earth's magnetic field is around 30 to 60 microtesla, which is enough to align compasses.
• Magnetic fields in astrophysics: Stars, planets and galaxies generate magnetic fields with sometimes extremely high flux densities.
• Polar lights: The interaction of charged particles with the Earth's magnetic field leads to the impressive light shows at high latitudes.

Interesting facts about magnetic flux density

Did you know that the strongest artificially generated magnetic fields reach flux densities of over 1,000 Tesla? Such magnetic fields are used in high-energy physics to study the behaviour of matter under extreme conditions.