The atomic number of a monatomic metal is equal to z. Consider a block of mass m of this metal. If the metal is neutral, the total number of positive charges equals the total number of negative charges, that is, the total number of electrons equals the total number of protons. Obtain an expression for calculating the positive charge on this material.

We have three identical metallic spheres insulated from each other. Two of them, A and B, are charged with charges equal to Q, and the third C is electrically neutral. The sphere C is brought into contact with A and then, C with B. Determine, in these conditions, the electric charge of C.

We have three identical conducting spheres insulated from each other. The electric charge on sphere A is equal to 12 μC, sphere B has a charge equal to 9 μC, and sphere C has a charge equal to −3 μC. The following operations are performed with these spheres:
1 – The three spheres are placed in contact simultaneously for a certain time and then separated;
2 – Sphere B is connected to the ground and then isolated;
3 – Spheres B and C are placed in contact and separated;
4 – Spheres A and C are placed in contact and separated.
Determine, in these conditions, the final charges of the spheres.