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Helmholtz coils
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Two coils giving near uniform field.
Two identical coils separated by their radius produce a nearly uniform field in the centre: B = (4/5)^{3/2} μ₀NI/R.
Used to cancel Earth's field and in experiments.
Uniform over a small volume only.
In more detail
Helmholtz coils are two identical coaxial coils separated by their radius, producing a nearly uniform field between them. They are used to calibrate magnetic sensors and cancel external fields.
Real-world uses
- Physics labs use Helmholtz coils to produce uniform fields.
- Sensor calibration uses them to set known field strengths.
- Physics labs use Helmholtz coils to produce a uniform field over a region for testing sensors.
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Frequently asked questions
Why separate them by the radius?
That spacing makes the second derivative of the field vanish at the centre, giving uniformity.
Is the field exactly uniform?
Only approximately, but very good in the central region.
Why are two coils used?
Two identical coils separated by their radius produce a much more uniform field than a single coil.
Related topics in Magnetism & Induction
Field of a solenoid · Toroid · Ampere's law · Magnetic dipole moment · Magnetic materials · Ferromagnetism and domains