How Do You Calculate the Charge and Number of Excess Electrons on a Pith Ball?

[ehdubbya]

Homework Statement

My problem states that a pith ball hangs at 20 degrees from the verticle and weighs 3 grams. It is moved 10cm by a charged rod. They both have the same charge. It asks what is the charge on the ball in C and approximatley how many excess electrons are on the ball.

Homework Equations

I have the equation kqq/rsquared

The Attempt at a Solution

I found all the sides to the triangle and I do not know where to go from there. I do not know the charges so how can I use the equation with q in it?

 

[quantumdude]

It is moved 10cm by a charged rod.

10 cm in which direction? x? y? other? And where is the rod in relation to the ball? Is the charge distributed over the entire rod, or is it concentrated at a point?

I found all the sides to the triangle and I do not know where to go from there. I do not know the charges so how can I use the equation with q in it?

Did you draw a free-body diagram and set up the equations from Newton's second law? You should have 2 equations in 2 unknowns (q and the tension T in the cord from which the ball hangs).

 

[Moetasim]

I would approach this problem by first identifying and defining all the variables involved. In this case, the variables are the angle of the pith ball (20 degrees), its weight (3 grams), and the distance it was moved (10cm). Additionally, the problem states that the pith ball and the charged rod have the same charge, but the value of this charge is not given.

Next, I would use the equation kqq/rsquared to calculate the charge on the pith ball. However, since the value of q is unknown, I would use algebra to rearrange the equation and solve for q. This would give us the charge on the pith ball in Coulombs (C).

To determine the number of excess electrons on the ball, we can use the fact that one electron has a charge of 1.602 x 10^-19 C. By dividing the total charge on the ball (calculated in the previous step) by the charge of one electron, we can determine the number of excess electrons on the ball.

It is important to note that this solution assumes that the pith ball and the charged rod have point charges, and that the pith ball is small enough that its position does not significantly affect the electric field. If these assumptions do not hold, the solution may be more complex and require additional information.