# How Do You Calculate Net Electric Flux Through a Cube?

• Kurtis McIntosh
In summary: You can calculate the charge from the net flux.In summary, to find the net electric flux through the cube, you need to sum up the fluxes of each face, taking into account the direction of the fields and assigning a positive or negative sign. The net charge in the cube can then be calculated from the net flux using Gauss' Law.
Kurtis McIntosh

## Homework Statement

Assume the magnitude of the electric field on each face of the cube of edge L = 1.07 m in the figure below is uniform and the directions of the fields on each face are as indicated. (Take E1 = 35.1 N/C and E2 = 25.3 N/C.)

A.) Find the net electric flux through the cube.

B.) Find the net charge in the cube.

## Homework Equations

Electric Flux = Electrical Field * Area

## The Attempt at a Solution

I don't really understand how to solve for the net electric flux in the problem. I thought you would just take the difference in forces for each direction, multiplied by the area, then solve to find the magnitude using the x and y fluxes, but I'm clearly missing something here. I've included a photo of the cube. I've also tried solving for the flux on each individual face and then finding the sum of the fluxes, but that doesn't seem to work either.

#### Attachments

• Capture.JPG
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Hi Kurtis, Welcome to Physics Forums.

Your Relevant Equation holds the key. The flux through a given area is given by the field strength multiplied by the area (for a uniform field over the area, you need to get fancier and do an integration if the field is not uniform). Note in the diagram that some fields are directed out of the face while others are directed into the face. That is to say, some flux is leaving the cube and some is entering it.

Assign a positive sign to flux leaving the cube and a negative sign to flux entering. Sum them up (algebraically).

If there is a net flux leaving or entering then there must be a charge inside the cube (See Gauss' Law).

## 1. What is the definition of net electric flux for a cube?

Net electric flux for a cube is a measure of the electric field passing through the surface of a cube. It is calculated by taking the dot product of the electric field vector and the surface area vector of the cube.

## 2. How is net electric flux for a cube calculated?

Net electric flux for a cube is calculated by taking the integral of the electric field vector over the surface of the cube. This integral is also known as the flux integral.

## 3. What are the units of net electric flux for a cube?

The units of net electric flux for a cube are Nm2/C, which can also be written as Vm.

## 4. How does the orientation of the cube affect the net electric flux?

The orientation of the cube does not affect the net electric flux. This is because the electric field vector and the surface area vector are always perpendicular, regardless of the orientation of the cube.

## 5. Can the net electric flux for a cube be negative?

Yes, the net electric flux for a cube can be negative. This occurs when the electric field vector and the surface area vector are in opposite directions, resulting in a negative dot product. This indicates that the electric field is leaving the cube, rather than entering it.

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