# Coulomb's Law/Newton's Law of Universal Gravitation (Precalculus?)

1. Jul 9, 2013

### Bill Nye Tho

1. The problem statement, all variables and given/known data
The electric field, E, a distance D away from a charged particle is directly proportional to the size of the charge Q, and inversely proportional to the square of the distance D. If the charge is increased by 40% and the distance is increased by 30%, by what percentage does the electric field change?

2. Relevant equations

???

3. The attempt at a solution

I'm actually pretty upset with how rusty I am at this but for some reason when I read these problems (and precalculus gravitational problems), I can't seem to get Classical Mechanics and Electromagnetism equations out of my mind. Although, I know that the answer will pretty much apply Coulomb's Law. Maybe I'm overthinking this..

ED = Q = 1/D^2

+.35(Q)
+.2(D)

Is all I'm interpreting from the question.

2. Jul 9, 2013

### SteamKing

Staff Emeritus
What do +.35(Q) and +.2(D) mean?

3. Jul 9, 2013

### Bill Nye Tho

Ah, I'm sorry.

I meant to write +.4Q and +.3D.

I'm increasing the charge by 40% and the distance by 30%

4. Jul 9, 2013

### Dick

If you increase Q by 40% then Q becomes 1.4Q. The original electric field is E=kQ/D^2. Compute the ratio of the new field to the original field.

5. Jul 9, 2013

### Bill Nye Tho

I know that, I'm just separating the added charge and added distance from the setup because I'm not even sure if I have that done correctly.

6. Jul 9, 2013

### Dick

That you understand it would be pretty hard to tell when you write things like +.35(Q) and +.2(D). If you know the ratio of initial and final charges and distance then use Coulomb's formula to compute the ratio of electric fields. This is pretty straightforward.

7. Jul 9, 2013

### Bill Nye Tho

I think I figured it out, with your help. Thanks