Magnetic fields and electromagnetism
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Explainer Video
Summary
Magnetic fields and electromagnetism
In a nutshell
Magnetic fields are fields that surround magnets and electric currents which exert a force on magnetic objects.
Magnetic fields
A magnetic field is a field that surrounds permanent magnets and electric currents and exerts a force on magnetic objects. They are normally represented by magnetic field lines which map magnetic field patterns and are helpful to interpret the strength and direction of the force.
Magnetic field lines have a few rules:
- The arrows on a magnetic field line always points from North to South.
- If the lines are parallel and equally spaced then the field is uniform.
- The denser the magnetic field lines the stronger the field.
- Like poles repel and unlike poles attract.
Below is an image showing the field lines around a bar magnet:
Electromagnetism
Anytime a charged particle moves, it produces a magnetic field around it. In permanent magnets, the field is produced by electrons moving around the nuclei, while all the atoms are lined up.
Right-hand grip rule
A current carrying wire produces a field with circular shapes around it. The direction of the magnetic field and current can be found with the right-hand grip rule:
- The thumb points in the direction of the current.
- The curl of the fingers in the direction of the field.
The graphic below demonstrates the right-hand grip rule.
Magnetic field lines for a flat coil
A flat coil of current carrying wire gives a field with the North and South poles above and below the coil:
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Magnetic field lines for a solenoid
The field around a long solenoid is similar to that of a bar magnet but with a uniform field inside it.
FAQs - Frequently Asked Questions
What are magnetic fields?
A magnetic field is a field that surrounds magnets and electric currents. It exerts a force on magnetic objects.
What is the right-hand grip rule?
The right-hand grip rule is a method to tell the direction of the magnetic field around a wire; the thumb represents the direction of the current while the curl of the fingers represents the direction of the field.
What is the shape of the magnetic field around a solenoid?
The magnetic field around a solenoid is very similar to the magnetic field around a bar magnetic but with a uniform field inside it.