# Homework Help: Charged-ring formula problem

1. Feb 2, 2010

### Jeff18

1. The problem statement, all variables and given/known data

A ring having a 10cm radius has a positive uniform density charge of 119,37 uC/m. Determine the electric field on the ring's axis at 5cm from the center of the ring.

2. Relevant equations

I used the equation E=2pi kad sigma/(a^2+ d^2)^(3/2). My question is related to the kad symbol. Does it have a real importance, and if so, what is it significance and how can I use it?!
Thanks
3. The attempt at a solution

2. Feb 2, 2010

### gabbagabbahey

Hi Jeff, welcome to PF !

I think you'll find that you will have much more success in your Physics studies if you make an effort to understand the formulas and their derivations rather than just looking them up or memorizing them. In this case, it seems as though you have simply looked up a formula in your text or on the internet, without even taking the time to look at which symbols the author is using for which constants and variables; let alone applying any of the physics knowledge your course likely has been teaching to derive the formula yourself.

Now, that being said; $kad$ is not even a symbol, but rather 3 symbols ($k$, $a$ and $d$) multiplied together. $$k=\frac{1}{4\pi\epsilon_0}$$ is Coulomb's constant, and the other two symbols are the radius of the loop and the distance along the loop's axis to the field point.

Again, I strongly recommend that you take the time to study the relevant chapters of your textbook and try your hand at deriving this formula yourself!

3. Feb 2, 2010

### Jeff18

Thanks! I realized i made that mistake right after posting my question! The characters in my textbook were real tight! ;) Thanks also for the advice of understanding formulas rather than memorize them! Though that's what i usually do, it's always good to have someone remind you! ;)