# Homework Help: What is Gauss's Law?

1. May 15, 2005

### elevated

I'm a senior in high school, and I have a physics research paper due on Thursday. The problem is, I don't know what Gauss's Law is.

In physics, Gauss's law gives the relation between the electric flux flowing out a closed surface and the charge enclosed in the surface.

I still don't know what it is.

Can someone explain in laymen's terms please?

2. May 15, 2005

### zeronem

You can't really explain that in Layman's Terms. You could, but heres some advice.

There are words stated in Gauss's Law that you could take the liberty in looking up there meanings in a Physics Book. For instance, you probably don't know what Electric Flux is, hence look in your Physics Book and read about electric flux. This is what Researching is all about. Find your sources, figure it out. Look up the meaning to the words you don't know, Do the Research.

3. May 15, 2005

### elevated

Thanks. I've managed to figure it out - basically, Gauss' law tells you how much electrical energy is leaving an object by considering the amount of charge held within the object and the material's permittivity.

My problem now is, what are some real-life applicatoins to Gauss's law? My physics teacher told me that this would be a good topic to write about because there was a lot to talk about. Doesn't seem like it to me

Ed

4. May 15, 2005

### Dr.Brain

The Basic Equation for Gauss Law is given by:

$\int B.dl = \frac {Q}{\varepsilon}$

where Q= net charge inside the Gaussian Surface.

A Gaussian Surface is an imaginary surface , according to your convenience.It is often convenient to construct an imaginary surface called a Gaussian surface to take advantage of the symmetry of the physical situation. For example it is a bit difficult to find out Electric Field at a point which is at "r" distance from an infinite plane of an infinite charged sheet , but using Gauss Law it is just a two line calculation.

You can find some examples of using Gauss Law in various questions.Another good application of this law is finding Electric Field inside a shell or a solid sphere within minutes at any point inside the shell of the solid charged sphere.

Example Of A Charged Spherical Shell:

Use the above equation Of gauss Law, as you know that net charge inside a shell is always zero, therefore the flux through the shell is zero and also the electric field.

5. May 15, 2005

### OlderDan

$\oint E \bullet dA = \frac {Q}{\epsilon_0}$

The left side of

$\oint B \bullet dl = \frac {Q}{\epsilon}$

would be appropriate for an Ampere's law calculation for magnetic fields

$\oint B \bullet dl = {\mu_0}i$

Last edited: May 15, 2005
6. May 15, 2005

### Staff: Mentor

No, not energy. No energy "flow" or transfer is involved here. In fact no "flow" or transfer of anything is involved here, at least if you're dealing with a situation where the charges are all stationary.

Although the word "flux" originates in the study of the physical motion of fluids, in this context it's just a useful quantity that helps describe the relationship between a vector field (such as the electric field) and a surface in space (which can be either a real surface or a conceptual one).

By now you've probably seen diagrams showing 'electric field lines" that radiate outward from or inwards towards electric charges. Mathematically speaking, these lines have much in common with the "streamlines" or "flow lines" that we might use to describe the motion of a fluid. That's why we use terms like "flux" when talking about both of them. But the similarity is just a mathematical one.

7. May 15, 2005