Solving for Charge Distribution on Charged Aluminum Spheres

In summary, the problem is that the user is struggling to understand how to solve a problem on MasteringPhysics (such wonderful software...) and is looking for guidance on the internet. There is no example problem like this in the book, and the user is getting no feedback from MP. The user estimates that there is a force of 1*10^24 (roughly one ton), but is unable to find the answer in the software.
  • #1
Gaupp
10
0
I'm having difficulty with a problem on MasteringPhysics (such wonderful software...) and as a last resort I'm posting on here. This is, I'm sure, a really simple problem but I'm getting no kind of feedback from MP and there isn't an example problem like this in the book.

The Problem

Two aluminum spheres of mass .025 kg are separated by 80 centimeters.

A) How many electrons does each sphere contain?

B)How many electrons would have to be removed from one sphere and added to the other to cause an attractive force between the spheres of magnitude 1.00 x 10^4 (roughly one ton)? Assume that the spheres may be treated as point charges.

C)What fraction of all the electrons in one of the spheres does this represent?

Attempted Solutions

A) I found Part A to be 7.25 x 10^24 electrons.

B) This is where I'm stuck.

If you were to remove electrons from one sphere and put them on the other I understand that their charges are to be equal but opposite, as in q1 = -q2. So using Coloumb's Law (F=K*q1*q2/(r^2)) I've set the Force to 1*10^4, divided that by K=9*10^9.

10000/(9*10^9) = q1*q2/(.8^2)

Then multiplying that by .8^2, I have just the charges on the other side of the equation. Since the charges in the formula are absolute value I can set q1=q2 and have q1^2. Taking the square root of the entire thing I have:

q=8.4327*10^-4.

So now I can use the formula q=e(#protons-#electrons). So:

8.4237*10^-4 = 1.6*10^-19(7.25*10^24-#electrons). Solving from this I get 7.249*10^24 electrons as my final answer.

However, MP says I'm wrong but there isn't any feedback as to where I went wrong, and it seems straightforward enough to me that no matter how I rework it I get the same thing every time.

Can anyone help me out here?

C) Can't do this one until B is done.
 
Last edited:
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  • #2
Oops. I think I posted this in the wrong forum. Can a mod or someone move this for me please?
 
  • #3
magnitude 1.00 x 10^24 (roughly one ton)?
I think you have this wrong, one ton force = 10,000 Newtons , 10^24N is a lot of force!
 
  • #4
mgb_phys said:
I think you have this wrong, one ton force = 10,000 Newtons , 10^24N is a lot of force!


Ok. Yeah I typed that in wrong. It should be 1*10^4 N. Thanks.
 

1. What are charged aluminum spheres?

Charged aluminum spheres are spherical objects made of aluminum that have been given an electrical charge. This charge can be either positive or negative and is typically created by rubbing the spheres against another material, such as silk or wool.

2. How are charged aluminum spheres used in scientific experiments?

Charged aluminum spheres are commonly used in electrostatic experiments to demonstrate the principles of electric charge and attraction. They can also be used to study the behavior of electric fields and the effects of charge on other objects.

3. What is the significance of using aluminum for these spheres?

Aluminum is a good conductor of electricity, meaning that it allows electric charge to flow through it easily. This makes it an ideal material for creating charged spheres as the charge can be evenly distributed on the surface of the sphere.

4. How do charged aluminum spheres differ from non-charged ones?

The main difference between charged and non-charged aluminum spheres is the presence of an electric charge on the surface. Non-charged spheres do not have this charge and therefore do not exhibit the same electrostatic effects as charged spheres.

5. Can the charge on aluminum spheres be reversed?

Yes, the charge on aluminum spheres can be reversed by bringing them into contact with an object of opposite charge. This process is known as induction and is commonly used in electrostatic experiments to demonstrate the attraction and repulsion of electric charges.

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