# A electric charge question for two spheres

1. Aug 12, 2014

### bennyq

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

A metallic sphere A of radius 1.00 cm is several centimetres away from a metallic spherical shell B of radius 2.00 cm. Charge 450 nC is placed on A, with no charge on B or anywhere nearby. Next, the two objects are joined by a long, thin, metallic wire, and finally the wire is removed. How is the charge shared between A and B?
a. 225 nC on A and 225 nC on B.
b. 90.0 nC on A and 360 nC on B, with equal surface charge densities.
c. 0 on A, 450 nC on B.
d. 150 nC on A and 300 nC on B.
e. 450 nC on A and 0 on B.

2. Relevant equations

3. The attempt at a solution
My attempt was to determine the charge density when the two spheres are connected. Since they are both conudctors I took the fact that all the charge would be on the surface of both spheres. So dividing the charge Q by the total surface area of both spheres, gives a ratio of 1/4 of surface are for sphere A to sphere B. So 90/360, missing something here. thanks
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

2. Aug 12, 2014

### bennyq

I think i worked this one out, when they are connected by the wire the potentials are equal so V1=V2, simplifys to
$\frac{Q1}{Q2}$=$\frac{r1}{r2}$=$\frac{σ2}{σ1}$