Question

Electrostatics Equilibrium Problem-It is required to hold four equal point charges +q each in equilibrium at the corners of a square. Find the point charge that will do this if kept at the center of the square?
I am doing the basics of coulomb's law,can anyone explain this to me?
I cannot do this problem,the problem seems to be complex to me?

Answer 1

There are a few pieces of basic knowledge that you need, to answer this question.
Firstly there is Coulomb's law, which tells you what force one charge feels due to one other charge a certain distance away.
Remember that force is a vector quantity, so it has a direction as well as a size (magnitude).
In this problem you need to find the total force on a charge coming from all the other charges around it, so you need to be able to add vectors by taking components along a particular direction.
It helps to be clear about the dimensions of a square - how far is it from the centre to a corner ? How far is it from one corner to another corner across the diagonal ?
And finally you need to understand what it means when we say a charge is in equilibrium - what does that say about the forces acting on the charge ?

Then you can start to solve this particular problem.

Answer 2

Yes i know the coulomb's law.
Half the diagonal is a/root 2.
Yes ,i liked ur concepts.
But,kindly help me more

Answer 3

Ok, so we want the charges to be in equilibrium, right ?
So if we pick one of the charges on the corner of the square, what can we say about the total force on that charge, if it is in equilibrium ?

Answer 4

zero

Answer 5

Yes, and so if i wanted the component of the total force on the charge in some direction, what would that be ?

Answer 6

that i donot know.

Answer 7

If i tell you that a vector is zero, what is its component in any direction ?

Answer 8

Let me make the question a bit more specific, suppose a vector represents a change of position - then the x component of the vector would tell you how much the position changed in the x direction, right ?

Answer 9

Yes,of course.

Answer 10

Ok, so now suppose i tell you that the change of postion vector is zero. How much did the postion change in the x direction ?

Answer 11

No,change along the x-axis.
can u draw a diagram

Answer 12

@ProfBrainstorm

Answer 13

What I'm saying is, if a vector is zero, then its component in any direction must be zero.
You will need that to solve your electrostatics problem.

Answer 14

Now you should draw a diagram for yourself of the charges arranged in your problem.

Answer 15

This much i could draw the center charge is Q.