Magnetic field: The invisible force around a magnet

A magnetic field is the area around a magnet or a current-carrying conductor in which magnetic forces act. It is a fundamental property of magnetism and is represented by so-called field lines, which visualise the course of the magnetic forces. A magnetic field influences ferromagnetic materials such as iron or nickel and charged particles.

How is a magnetic field created?

Magnetic fields are created by moving electrical charges or magnetised materials:

• Permanent magnets: In permanent magnets, the magnetic field is created by the alignment of the magnetic moments in the atoms.
• Electromagnets: Current-carrying conductors generate magnetic fields according to the right-hand rule. The direction of the magnetic field depends on the direction of the current.
• Moving charges: Charged particles that move generate magnetic fields. This is the basis for electrodynamics.

Properties of a magnetic field

• Vectorial quantity: A magnetic field has both a strength and a direction, which is indicated by the field lines.
• Field lines: Magnetic field lines are closed loops. They emerge from the north pole of a magnet and enter the south pole.
• Strength of the magnetic field: The magnetic flux density is measured in the unit Tesla (T). Weak fields such as the earth's magnetic field have values in the microtesla range, while MRI devices generate fields of up to 7 tesla.
• Range: Magnetic fields become weaker with increasing distance from the magnet.

Representation of a magnetic field

The direction and strength of a magnetic field are illustrated by magnetic field lines:

• Direction: The field lines point from north to south.
• Density: The density of the field lines indicates the strength of the magnetic field. The denser the lines, the stronger the field.

Applications of magnetic fields

Magnetic fields play a central role in many technical and everyday applications:

• Electric motors and generators: Magnetic fields are the basis for converting electrical energy into mechanical energy (and vice versa).
• Magnetic resonance imaging (MRI): Strong magnetic fields are used in medicine to generate detailed images of the human body.
• Data storage: Hard drives and magnetic tapes use magnetic fields to store data in the form of magnetised areas.
• Navigation: The Earth's magnetic field enables the use of compasses to determine cardinal points.

Magnetic fields in nature

Magnetic fields are not only a technical phenomenon, but are also omnipresent in nature:

• Earth's magnetic field: The earth generates a magnetic field that protects us from solar radiation and is the basis for navigation with compasses.
• Aurora Borealis: The interplay of solar winds and the Earth's magnetic field causes the impressive auroras.
• Astrophysics: Magnetic fields influence the dynamics of stars, planets and galaxies.

Interesting facts about magnetic fields

Did you know that the strongest magnetic field generated by humans reaches over 1,200 Tesla? Such extreme magnetic fields are used in research to study the behaviour of matter under extreme conditions.