# Homework Help: Point charges

1. May 12, 2012

### cuddlylover

Point charges q1 and q2 lie on the x axis at points x = -a and x = +a, respectively. (a) How
must q1 and q2 be related for the net electrostatic force on point charge +Q, placed at x = +a=2,
to be zero? (b) Repeat (a) but with point charge +Q now placed at x = +3a=2.

Can someone help me with this i am a bit lost.

2. May 12, 2012

### Infinitum

What is the electrostatic force on Q due to charge q1? and due to q2??

Then apply the superposition principle.

3. May 12, 2012

### cuddlylover

If someone could go in to more detail on this would be a big help

4. May 12, 2012

### Infinitum

Electrostatic force(Coulomb's Law) : http://en.wikipedia.org/wiki/Coulomb's_law

Superposition principle states that electrostatic force between any two charges is independent of other charges. The force on any charged particle due is given by the vector addition of the force due to each charge.

${F_{net}} = {F_1} + {F_2} + {F_3} + ....... + {F_n}$

5. May 13, 2012

### vela

Staff Emeritus
That's not how it works here. Infinitum's given you two nudges. Now you need to step up and show some initiative on solving this problem yourself first.