# 2: Electric and Magnetic Fields

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• 2.1: What is a Field?
A field is the continuum of values of a quantity as a function of position and time.
• 2.2: Electric Field Intensity
Electric field intensity is a vector field we assign the symbol E and has units of electrical potential per distance; in SI units, volts per meter (V/m). Before offering a formal definition, it is useful to consider the broader concept of the electric field.
• 2.3: Permittivity
Permittivity describes the effect of material in determining the electric field in response to electric charge.
• 2.4: Electric Flux Density
Electric flux density, assigned the symbol D , is an alternative to electric field intensity ( E ) as a way to quantify an electric field.
• 2.5: Magnetic Flux Density
Magnetic flux density is a vector field which we identify using the symbol B and which has SI units of tesla (T). Before offering a formal definition, it is useful to consider the broader concept of the magnetic field. Magnetic fields are an intrinsic property of some materials, most notably permanent magnets.
• 2.6: Permeability
Permeability describes the effect of material in determining the magnetic flux density. All else being equal, magnetic flux density increases in proportion to permeability.
• 2.7: Magnetic Field Intensity
Magnetic field intensity H is an alternative description of the magnetic field in which the effect of material is factored out.
• 2.8: Electromagnetic Properties of Materials
The electromagnetic properties of most common materials in most common applications can be quantified in terms of the constitutive parameters ϵ , μ , and σ, which are the teh Permittivity, Permeability and Conductivity. These are the three constitutive parameters, which describe the effect of material in determining an electromagnetic quantity in response to a source.

Thumbnail: The magnetic field of a current-bearing coil, illustrating field lines. (CC BY 4.0; Y. Qing).