# Electric flux

1. Aug 12, 2014

### tecnics

what is meant by electric flux...

and how does an electric flux gets 'cancelled'????

can a electric flux exist even when electric field is zero??

2. Aug 12, 2014

### Staff: Mentor

If you tell us a definition that you've seen already, and what you don't understand about it, people here will probably be more likely to help you.

3. Aug 13, 2014

### tecnics

i know only much enough that..

\\\electric flux is .. a integral of surface and electric field of that conductor.
the electric field can be internal or external....

after dis..i cant understand anything about electric flux......

can anyone tell me how to....imagine electric flux...like some field lines or something???

currently i am unable to imagine it in any form...and thus ..i am not able to understand its concept.

4. Aug 13, 2014

### Staff: Mentor

First, understand that a field is a way of mathematically describing how objects will interact in space and time. The field has a value at every point in space and time for quantities such as the magnitude and direction of the electric force. Field lines (aka flux lines) are a way of visually representing this field since trying to imagine a bunch of numbers everywhere isn't really possible or helpful. Note that field lines are similar to latitude and longitude lines in that they aren't actual real objects. They simply help show how strong the field is and in which direction it is pointing.

Electric flux is defined as the rate of flow of the electric field through a given area, and is proportional to the number of field lines passing through a surface. The greater the number of field lines, the stronger the field. So in this case the field lines represent the electric flux, which is the strength and direction of the electric field through a surface, and you can find out how strong the field is at any point by counting the number of field lines passing through the surface the point is on.

http://en.wikipedia.org/wiki/Field_line
http://en.wikipedia.org/wiki/Electric_flux

5. Aug 13, 2014

### Okefenokee

Flux simply means something is flowing.

Imagine that you place some sort of ring in a river and measure how much water flows through it. Let's say the result is something like 50 gallons an hour. You could call that a water flux. Now consider what happens if you turn the ring so that it is parallel with the current. No water would pass through it so now you have 0 water flux.

If you mapped the directions and speeds of the currents in the river down to the smallest detail then you should in theory be able to calculate the flux through a ring placed anywhere in the river. That map of water currents is like the electric field.

Keep in mind that what I described is an analogy. Water flows in a river but the electric field isn't something that is flowing. It's a force. You could say that electric flux is a sum of the electric fields force acting on some surface.

The electric field is a vector field but notice that electric flux is a scalar. Going back to the water example, if you measure 50 gallons/hour of water flux going through a ring the figure that you get doesn't tell you anything about where all the water was going. Maybe 100 g/hr was going North through one half of the ring and 150 g/hr was going South through the other half. Because they were going in opposite directions they cancel and you only measured a total of 50 gallons/hr of water flux heading South.

6. Aug 13, 2014

### Delta²

To understand electric flux, you have first to understand the concept of field lines or the fact that the electric field is a vector field or both :). Electric flux is simpy how many field lines pass through the surface (of which surface we want to calculate the electric flux through).

So electric flux depends not only on the electric field but also on what surface we choose to calculate the flux that is passing through that surface.

If the electric field is zero over the surface of interest then the flux through that surface is zero also.

However it can be the case that the total flux through a surface is zero but the electric field is not zero in all the points of the surface. To imagine how this can happen you have to think of a closed surface like the surface of a sphere. Imagine that you put this imaginary sphere inside a charged capacitor. The electric field lines will enter inside the sphere from one hemisphere (this creates a negative electric flux because the field lines are entering inside ) and will exit from the other hemisphere (this creates an equal and positive electric flux because the field lines are exiting). The total flux will be the sum of flux for one hemisphere and for the other, and will be zero.