
Electric flux is a property of an electric field that can be thought of as the number of electric lines of force (or electric field lines) that intersect a given area. The mathematical relationship between enclosed charge and electric flux is called Gauss's law. The SI base unit of electric flux is volt-meters (V·m), or newton-meter squared per coulomb (N·m²·C⁻¹). The electric flux through an area of an element is given by the formula Φ=EAcosθ. This formula shows that electric flux depends on the electric field, the area of the surface, and the angle between the electric field lines and the normal (perpendicular) to the surface.
| Characteristics | Values |
|---|---|
| Definition | A property of an electric field that can be thought of as the number of electric lines of force (or electric field lines) that intersect a given area |
| Formula | Φ=EAcosθ |
| Factors | Electric field, magnitude of the electric field, area of the surface, and the angle between the electric field lines and the normal (perpendicular) to the area |
| Unit | Volt-meter (V·m) or newton-meter squared per coulomb (N·m2·C−1) |
| SI base unit | voltmeters (V m) |
| Flux through left side | -0.04 Nm²/C |
| Flux through right side | +0.04 Nm²/C |
| Flux through top, bottom, front, and back sides | 0 Nm²/C |
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What You'll Learn
- Electric flux is the total number of electric field lines passing through a given area in a unit of time
- The SI unit of electric flux is the volt-metre (V·m)
- The electric flux passing through a surface is given by the formula Φ=EAcosθ
- The electric flux through the left side is negative, while the right side is positive
- Gauss's law makes use of the concept of electric flux

Electric flux is the total number of electric field lines passing through a given area in a unit of time
Electric flux is a property of an electric field that can be thought of as the total number of electric field lines passing through a given area per unit of time. It is a measure of how much of something passes through a given area. The concept of flux is always defined based on a surface and a vector field (in this case, the electric field). The larger the area, the more field lines go through it, and hence, the greater the flux. Similarly, the stronger the electric field, the greater the density of lines, and the greater the flux.
The SI unit of electric flux is the volt-meter (V·m), or, equivalently, newton-meter squared per coulomb (N·m2·C−1). The unit of electric flux expressed in terms of SI base units is kg·m3·s−3·A−1. Flux can also be used to describe the amount of sunlight hitting a solar panel or the amount of energy a telescope receives from a distant star.
The definition of flux is given by the formula:
> \(\Phi = \vec{E} \cdot \vec{A} \ (\text{uniform } \vec{E})\)
Where \(\Phi\) is the flux, \(\vec{E}\) is the electric field, and \(\vec{A}\) is the area vector. For a uniform electric field, the electric flux passing through a surface of vector area A is:
> \({\displaystyle \Phi _{\text{E}}=\mathbf {E} \cdot \mathbf {A} =EA\cos \theta}\)
Where E is the electric field (having the unit V/m), E is its magnitude, A is the area of the surface, and \(\theta\) is the angle between the electric field lines and the normal (perpendicular) to A.
For a non-uniform electric field, the electric flux \(\Phi_E\) through a small surface area dA is given by:
> \({\displaystyle {\textrm {d}}\Phi _{\text{E}}=\mathbf {E} \cdot {\textrm {d}}\mathbf {A} }
Where dA is the component of area perpendicular to the field.
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The SI unit of electric flux is the volt-metre (V·m)
Electric flux is a property of an electric field that can be thought of as the number of electric field lines that intersect a given area. The electric flux through a surface is directly proportional to the total number of electric field lines going through that surface.
The electric flux through a surface is calculated by multiplying the electric field (with the unit V/m) by the area of the surface. This calculation assumes that the surface is perpendicular to the flux lines. If the electric field is non-uniform, the electric flux is calculated by multiplying the electric field by the component of the area that is perpendicular to the field.
The normal vector of the left side of a surface points in the opposite direction to the electric field, resulting in a θ angle of 180°. The normal vectors of the top, front, and back sides are perpendicular to the electric field, resulting in a θ angle of 90°. Thus, the sides with non-zero electric flux are the right and left sides.
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The electric flux passing through a surface is given by the formula Φ=EAcosθ
Electric flux is a fundamental concept in electrostatics that measures the amount of electric field passing through a surface. It is akin to visualizing how water flows through a ring. The formula for electric flux is Φ=EAcosθ, where Φ is the electric flux, E is the electric field, A is the area of the surface, and θ is the angle between the electric field lines and the normal (perpendicular) to the surface.
The electric flux is influenced by the angle between the electric field and the surface's normal vector. When the electric field and normal point in the same direction, positive flux occurs, while negative flux occurs when they point in opposite directions. This can be observed in the right and left sides of a closed surface, where the electric flux has equal magnitudes but opposite signs.
For instance, consider a closed surface with an electric field strength of 100 N/C. The electric flux through the right side might be calculated as +0.04 Nm²/C, while the flux through the left side would be -0.04 Nm²/C. The top, bottom, front, and back sides, where the normal vectors are perpendicular to the electric field, result in a zero electric flux value.
The SI unit of electric flux is the volt-meter (V·m), or newton-meter squared per coulomb (N·m²·C⁻¹). This formula, Φ=EAcosθ, is a valuable tool for calculating and understanding electric flux, which is essential for applying Gauss's law in electrostatics.
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The electric flux through the left side is negative, while the right side is positive
Electric flux is a property of an electric field that can be thought of as the number of electric lines of force (or electric field lines) that intersect a given area. The mathematical relationship between enclosed charge and electric flux is known as Gauss's law. Flux is always defined based on a surface and a vector field (in this case, the electric field).
The electric flux through an area of an element is given by the formula: Φ=EAcosθ. From this formula, we can see that electric flux depends on the following factors: the electric field (E), its magnitude, the area of the surface (A), and the angle (θ) between the electric field lines and the normal (perpendicular) to A.
Now, let's consider a specific example to understand why "the electric flux through the left side is negative, while the right side is positive." Imagine an electric field with a strength of 100 N/C. On the left side, the normal vector points in the opposite direction to the electric field, resulting in an angle (θ) of 180 degrees. This means the electric flux through the left side is negative. On the other hand, the right side has a positive electric flux because its normal vector is directed outward, resulting in a positive value for θ.
In summary, the direction of the normal vector in relation to the electric field determines whether the electric flux is positive or negative for a given side. In this case, the left side has a negative electric flux due to the opposite directions of the normal vector and electric field, while the right side has a positive electric flux because its normal vector is directed outward.
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Gauss's law makes use of the concept of electric flux
Electric flux is a property of an electric field that can be thought of as the number of electric lines of force or electric field lines that intersect a given area. The SI unit of electric flux is the volt-metre (V·m), or, newton-metre squared per coulomb (N·m²·C⁻¹).
Mathematically, electric flux is defined as the electric field times the component of the area perpendicular to the field. A Gaussian surface is a surface through which the electric flux is calculated. By imagining a Gaussian surface that encloses a charge, we can observe the electric field at different points on this imaginary surface. Gauss's law is a relationship between the field at all the points on the surface and the total charge enclosed within the surface.
Common examples of symmetries that lend themselves to Gauss's law include cylindrical symmetry, planar symmetry, and spherical symmetry. Gauss's law is most useful for "by hand" calculations when high degrees of symmetry exist in the electric field.
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Frequently asked questions
Electric flux is a property of an electric field that can be thought of as the number of electric lines of force (or electric field lines) that intersect a given area.
The electric flux through an area of an element is given by the formula: Φ=EAcosθ.
Electric flux depends on the electric field (E), the area of the surface (A), and the angle (θ) between the electric field lines and the normal (perpendicular) to A.
The SI unit of electric flux is the volt-meter (V·m), or newton-meter squared per coulomb (N·m2·C−1).
The electric flux through the left side is given by Φ=EAcos(180°). If the electric field strength is 100 N/C, the electric flux through the left side is -0.04 Nm²/C.











































