# Homework Help: Find an expression for the electrostatic energy of this charge distribution.

1. Dec 14, 2012

### warnexus

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

2. Relevant equations
work = kqqq/(distance)

3. The attempt at a solution
http://i33.photobucket.com/albums/d86/warnexus/electrodiag.jpg

2. Dec 14, 2012

### Staff: Mentor

Check the distance you've used for the diagonals. Substitute 'q' and 'q/2' for the appropriate charges and simplify.

3. Dec 14, 2012

### warnexus

the distance I used for the diagonals is sqrt of a. I do not understand I do not have q/2.

4. Dec 14, 2012

### Staff: Mentor

Is the length of a diagonal of a square of side length a equal to √a ?

You have two sizes of charge: One is 'q', the other is 'q/2'. Make the appropriate symbolic substitutions.

5. Dec 14, 2012

### warnexus

oops the diagonal is suppose to be sqrt 2a^2.

heres the substitutions:

k(qq/a + qq/sqrt(2a^2) + qq/a -1/2qq/a -1/2qq/a -1/2qq/sqrt(2a^2))

Last edited: Dec 14, 2012
6. Dec 14, 2012

### Staff: Mentor

Okay, but you can simplify further. For example, you can pull out the q2 from each term.

7. Dec 14, 2012

### warnexus

heres the simplification

kqq(1/a + 1/sqrt(2a^2) + 1/a - (1/a) - (1/2)/sqrt (2a^2)

8. Dec 14, 2012

### Staff: Mentor

You can collect the terms, putting them over a common denominator...