# Homework Help: Electrostatics: Using a conducting string suspension.

1. Sep 18, 2012

### Dieinhell100

1. The problem statement, all variables and given/known data
This is a lab question.
Basically what the lab entails is we have two spheres. One is suspended from a string and another is attached to a non-conducting rod.

We inductively charge the sphere attached to the rod. Then we bring it close to the other sphere that is being suspended from a string and allow the two spheres to come in contact with each other briefly, leaving them both charged.

We bring the two spheres closely together so that the suspended sphere is repelled. We then measure the distance that the suspended sphere has moved from it's initial position (the difference is defined as X).

Pretty simple stuff.

However, on the lab there is a thought question. It gives us an equation for X (which is given below) and asks us what terms in the equation will be affected (and how) if we used a conducting string suspension for the sphere being suspended.

2. Relevant equations
X=(kl/mg)(Q^2/d^2)

Q^2 could also be written as (Q1*Q2). Q1 is the charge on the suspended sphere and Q2 is the charge on the sphere attached to the rod.
k is a constant equal to 8.99*10^9 Nm^2/C^2
l is the length of the string
m is the mass
g is the acceleration of gravity
d is the distance between the two spheres (whilst the repulsion is taking place)
And again, X is the distance between the initial position of the suspended sphere and the position once it's being repulsed.

3. The attempt at a solution
Well, I don't believe using a conducting string would change the mass, the force of gravity, the constant k, or the length of the string.
That just leaves X, Q, and d.

My first thought is does it really change Q? Doesn't it just spread the charge between the string and the sphere. I believe that Q only concerns the sphere. So would this mean the value of Q decreases?

Wouldn't the "decrease" in Q change the values of X and d?