1. May 7, 2007

The physical terms might not be the right english ones, I am not english. I hope you will understand anyway. I need help with the 3 following exercises, if anyone could dedicate some time to them I would be really grateful. Thank you.

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

1) Determine the electric and potential fields in all the space for a system composed of a sphere of radius=R, equally charged with charge=Q, surrounded by a spherical conductor crown with internal radius=R and external radius=r.

2) A proton is fired toward another proton, which is steady at a great distance, with speed v= 2.4 * 10^8 m/s. Find the minimal distance between the two protons.

3) We have a vertical electric field. How intense must it be and what direction must it have to hold a particle in equilibrium? The particle has mass = 10^-8 g and is charged with q= 1.7 * 10^-9 C.

Thank you very much in advance.

2. May 7, 2007

### Staff: Mentor

How about writing the applicable equations for each problem. What equations apply in each case?

In the first problem, it appears one has a 'spherical shell' conductor. There is an electric field inside, and one outside. What law applies?

In the second one proton starts far away from the other, so think about the total kinetic energy, conservation of energy, and the electric potential energy when both protons are at rest.

In the third problem, what is the significance of the force acting vertically, and what is its influence with respect to a particle's mass?