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Magnetic Fields

Magnetic Fields

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...

Energy In A Magnetic Field

Energy In A Magnetic Field

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 negligible.
The energy...

Motional Emf

Motional Emf

Magnetic flux depends on three factors: the strength of the magnetic field, the area through which the field lines pass, and the field's orientation with respect to the surface area. If any of these quantities vary, a corresponding variation in magnetic flux occurs. If the area through which the magnetic field lines are passing changes, then the magnetic flux also changes. This change in the area can be of two types: the flux through the rectangular loop increases as it moves into the magnetic...

Energy Carried By Electromagnetic Waves

Energy Carried By Electromagnetic Waves

Anyone who has used a microwave oven knows there is energy in electromagnetic waves. Sometimes, this energy is obvious, such as in the summer sun's warmth. At other times, it is subtle, such as the unfelt energy of gamma rays, which can destroy living cells. Electromagnetic waves bring energy into a system through their electric and magnetic fields. These fields can exert forces and move charges in the system and, thus, do work on them. However, there is energy in an electromagnetic wave,...

Electromagnetic Fields

Electromagnetic Fields

Electric fields generated by static charges, often referred to as electrostatic fields, are characteristically different from electric fields created by time-varying magnetic fields. While the former is a conservative field, implying that no net work is done on a test charge if it goes around in a complete loop in the field, the latter is, by definition, not a conservative field; net work is done, and it is proportional to the rate of change of magnetic flux.
However, the observation of Gauss's...

Electric Field of a Non Uniformly Charged Sphere

Electric Field of a Non Uniformly Charged Sphere

Gauss's law states that the electric flux through any closed surface equals the net charge enclosed within the surface. This law is beneficial for determining the expressions for the electric field for a particular charge distribution if the electric flux is known.
Consider a non-uniformly charged sphere, for which the density of charge depends only on the distance from a point in space and not on the direction. Such a sphere has a spherically symmetrical charge distribution. Here, the electric...

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Related Experiment Video

Updated: Jun 13, 2026

Near-Infrared Temperature Measurement Technique for Water Surrounding an Induction-heated Small Magnetic Sphere

Near-Infrared Temperature Measurement Technique for Water Surrounding an Induction-heated Small Magnetic Sphere

Published on: April 30, 2018

Electromagnetic energy within magnetic spheres.

Tiago José Arruda¹, Alexandre Souto Martinez

¹Faculdade de Filosofia, Ciências e Letras de Ribeirão Preto, Universidade de São Paulo, Avenida Bandeirantes 3900, 14040-901 Ribeirão Preto, São Paulo, Brazil.

Journal of the Optical Society of America. A, Optics, Image Science, and Vision

|May 8, 2010

Summary

Magnetic spheres exhibit significantly higher internal electromagnetic energy during resonance compared to nonmagnetic ones, even at small sizes. This study provides new analytical insights into magnetic scatterers and their unique properties.

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Electric and Magnetic Field Devices for Stimulation of Biological Tissues

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Last Updated: Jun 13, 2026

Near-Infrared Temperature Measurement Technique for Water Surrounding an Induction-heated Small Magnetic Sphere

Near-Infrared Temperature Measurement Technique for Water Surrounding an Induction-heated Small Magnetic Sphere

Published on: April 30, 2018

Electric and Magnetic Field Devices for Stimulation of Biological Tissues

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Published on: May 15, 2021

Area of Science:

Electromagnetism
Condensed Matter Physics
Materials Science

Background:

Electromagnetic scattering by particles is a well-studied phenomenon.
However, research on magnetic scatterers remains limited.
Understanding particle properties is crucial for various applications.

Purpose of the Study:

To derive exact expressions for time-averaged electromagnetic energy within a magnetic sphere.
To analyze the contributions of field components to internal energy.
To investigate the absorption cross-section in the weak absorption regime.

Main Methods:

Rigorous Mie theory applied to a homogeneous, isotropic magnetic sphere.
Derivation of exact analytical expressions for internal energy and absorption cross-section.
Analysis of electromagnetic field components and their energy contributions.

Main Results:

Magnetic scatterers show significantly higher resonance energy compared to nonmagnetic ones, especially at low size parameters.
Exact expressions for internal energy contributions from radial and angular fields derived.
An exact expression for absorption cross-section in terms of magnetic Mie internal coefficients obtained.

Conclusions:

Magnetic scatterers possess unusual properties with potentially significant implications for applications.
The findings provide new analytical results for magnetic particles.
Highlights the importance of considering magnetic properties in scattering phenomena.