### Electric Field Intensity (E)
Electric field intensity, often just called the
electric field, represents the force per unit charge exerted on a small positive test charge placed at any point in space. It tells you how strong the electric field is and in what direction it acts.
Mathematically, it's defined as:
\[
\vec{E} = \frac{\vec{F}}{q}
\]
Where:
- \( \vec{E} \) is the electric field intensity (measured in volts per meter, V/m)
- \( \vec{F} \) is the force experienced by the test charge (in newtons, N)
- \( q \) is the magnitude of the test charge (in coulombs, C)
Key Points:
- The electric field points away from positive charges and towards negative charges.
- The intensity is stronger the closer you are to the charge creating the field.
Electric Flux Density (D)
Electric flux density, denoted as
\( \vec{D} \), represents the amount of electric flux passing through a given area in space. It is directly related to the electric field intensity but also takes into account the material (like a dielectric) through which the field is passing.
Mathematically:
\[
\vec{D} = \epsilon \vec{E}
\]
Where:
- \( \vec{D} \) is the electric flux density (measured in coulombs per square meter, C/m²)
- \( \epsilon \) is the permittivity of the medium (in farads per meter, F/m)
- \( \vec{E} \) is the electric field intensity (V/m)
Key Points:
- The electric flux density accounts for the material's ability to store electrical energy in the presence of an electric field (its permittivity).
- In free space, the permittivity is denoted by \( \epsilon_0 \), but in other materials, it's \( \epsilon \), which is generally higher than \( \epsilon_0 \).
Summary of Differences:
- Electric Field Intensity (E) tells you about the force on a charge and is a vector quantity that only depends on the charge and distance.
- Electric Flux Density (D) tells you about the electric flux passing through an area, and it depends on both the electric field and the material's permittivity.
Does that help clarify the difference between them?