Question

what exactly is electric flux ? define it

Answer 1

Electric flux is a tricky concept to picture. Its definition is the flux of an electric field, this though does not clarify things much. We can break it down into two components. I presume that you are happy with what an electric field is and will know about electric field lines. The important point here is that the closer together the electric field lines, the stronger the electric field is at that point in space.

Flux is just a fancy way of saying the number of things passing through a given area in a given amount of time. For example we could have a particle flux whereby we could have 100 particles passing through one square centimetre every second.

Combining the two concepts we obtain the electric flux, which tells us how many field lines pass through a specific area at any one time. In electromagnetism though we use the concept of surfaces instead of areas, and so it is the number of field lines passing through a surface of specific area at any one time. The more electric field lines squeezed into that surface area, the greater the electric flux at that time.

Answer 2

Read the attached document

Answer 3

In electromagnetism, electric flux is the flux of the electric field. Electric flux is proportional to the number of electric field lines going through a virtual surface. The electric flux through a small area is given by

(the electric field, E, multiplied by the component of area perpendicular to the field). The electric flux over a surface S is therefore given by the surface integral:

Answer 4

Also important to point out that the electric flux through a closed surface surrounding a point charge q is not dependent upon the area of the surface. Imagine a charge, q inside a balloon. There are a finite number of field lines moving through the balloon's surface regardless of how much you inflate the balloon.
At a point P away from the balloon, however, the magnitude does drop off as \[1/r ^{2}\] .

Answer 5

if it is the number of electric field lines passing through a given area then which field lines does it mean ? can i field line in any orientation with many sources ?? and what exactly should be the direction of field lines through the area ?

Answer 6

It refers to all field lines, but usually you just consider the field lines relevant to that particular problem. The field lines can cut the surface in any orientation, but we only consider the component of the field that is parallel to the unit normal of the surface. And yes, many sources can be considered since their electric fields are vector quantities, and so can be combined vectorialy to give a resultant field. As for direction through the area,, the convention is to define the direction outwards along the unit normal of that area or surface, that is to say, field lines can be going both ways through a surface, but all calculations are performed relative to the outward pointing normal.

For more details on the electric flux see section 1.1 in "A Students Guide to Maxwell's Equations". A preview copy in .pdf format can be read here http://riyanto04.files.wordpress.com/2009/09/a-students-guide-to-maxwells-equations.pdf

Answer 7

thank you :)