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Related Concept Videos

Magnetic Fields01:27

Magnetic Fields

7.4K
A moving charge or a current creates a magnetic field in the surrounding space, in addition to its electric field. The magnetic field exerts a force on any other moving charge or current that is present in the field. Like an electric field, the magnetic field is also a vector field. At any position, the direction of the magnetic field is defined as the direction in which the north pole of a compass needle points.
A magnetic field is defined by the force that a charged particle experiences...
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Magnetic Field of a Solenoid01:18

Magnetic Field of a Solenoid

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A solenoid is a conducting wire coated with an insulating material, wound tightly in the form of a helical coil. The magnetic field due to a solenoid is the vector sum of the magnetic fields due to its individual turns. Therefore, for an ideal solenoid, the magnetic field within the solenoid is directly proportional to the number of turns per unit length and the current. Conversely, the magnetic field outside the solenoid is zero.
Consider a solenoid with 100 turns wrapped around a cylinder of...
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Magnetic Field Lines01:19

Magnetic Field Lines

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The representation of magnetic fields by magnetic field lines is very useful in visualizing the strength and direction of the magnetic field. Each of the magnetic field lines forms a closed loop. The field lines emerge from the north pole (N), loop around to the south pole (S), and continue through the bar magnet back to the north pole.
Magnetic field lines follow several hard-and-fast rules:
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Energy In A Magnetic Field01:24

Energy In A Magnetic Field

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If a magnetic field is sustained, there must be a current in a closed circuit or loop, implying some energy has been spent in creating the field. If this energy is not dissipated via the circuit's resistance, it is stored in the field.
Take an ideal inductor with zero resistance. Although it's practically impossible, assume that the coil's resistance is so small that it is practically negligible. The loss of the field's energy to dissipate thermal energy (or heat) is thus...
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Colors and Magnetism03:02

Colors and Magnetism

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Color in Coordination Complexes
When atoms or molecules absorb light at the proper frequency, their electrons are excited to higher-energy orbitals. For many main group atoms and molecules, the absorbed photons are in the ultraviolet range of the electromagnetic spectrum, which cannot be detected by the human eye. For coordination compounds, the energy difference between the d orbitals often allows photons in the visible range to be absorbed and emitted, which is seen as colors by the human...
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Magnetic Field Of A Current Loop01:16

Magnetic Field Of A Current Loop

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Consider a circular loop with a radius a, that carries a current I. The magnetic field due to the current at an arbitrary point P along the axis of the loop can be calculated using the Biot-Savart law.
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Related Experiment Video

Updated: Feb 11, 2026

Assessing Primary Motor Cortex Excitability and Excitability Modulation by Pairing Transcranial Magnetic Stimulation with Electromyography
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Assessing Primary Motor Cortex Excitability and Excitability Modulation by Pairing Transcranial Magnetic Stimulation with Electromyography

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Decrease of motor cortex excitability following exposure to a 20 Hz magnetic field as generated by a rotating

Eugen Gallasch1, Dietmar Rafolt2, Magdalena Postruznik1

  • 1Otto Loewi Research Center, Physiology Section, Medical University of Graz, Austria.

Clinical Neurophysiology : Official Journal of the International Federation of Clinical Neurophysiology
|May 6, 2018
PubMed
Summary

Rotating magnets create transcranial alternating magnetic fields (tAMF) that decrease motor cortex excitability. This novel brain stimulation method shows potential for clinical neurophysiology applications.

Keywords:
Electromagnetic inductionModulation of cortical excitabilityMotor cortexNoninvasive brain stimulationTMStACS

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Area of Science:

  • Neuroscience
  • Electrophysiology
  • Brain Stimulation

Background:

  • Transcranial magnetic stimulation (TMS) is a key tool in neuroscience.
  • Transcranial alternating current stimulation (tACS) influences cortical excitability.
  • The effects of transcranial alternating magnetic fields (tAMF) are less understood.

Purpose of the Study:

  • To investigate the influence of tAMF on motor cortex (MC) excitability.
  • To compare tAMF effects with those of tACS.
  • To explore tAMF as a novel brain stimulation tool.

Main Methods:

  • Fourteen healthy volunteers received 20 Hz tAMF and tACS over the MC.
  • TMS assessments measured motor evoked potentials (MEP), short interval intra-cortical inhibition (SICI), and intra-cortical facilitation (ICF).
  • Stimulations lasted 15 minutes, with assessments before and after.

Main Results:

  • tAMF stimulation over the MC decreased MEP amplitudes and ICF, while increasing SICI.
  • tACS stimulation over the MC increased MEP amplitudes without affecting SICI or ICF.
  • Single and paired pulse MEPs indicated a general decrease in MC excitability after tAMF.

Conclusions:

  • tAMF and tACS differentially affect cortical excitability.
  • tAMF stimulation leads to a decrease in MC excitability.
  • Rotating magnet devices show promise as a new tool in clinical neurophysiology.