An alpha particle (charge +2e, mass 6.64 ˛ 10-27 )moves head-on at a fixed gold nucleus (charge +79e). If the distance of closest approach is 2.0 ˛ 10-10 m, what was the initial speed of the alpha particle?

Three reasons for adding a dielectric material between the plates of a capacitor.
1. Dielectrics do not break down (allowing electric charge to flow"as readily as air, so a higher voltage can be applied without charge passing across the gap.
2. A dielectric allows the plates to be placed closer together without touching thus allowing an increased capacitance because the plate separation is less.
3. If a dielectric fills the space between the two conductors, it increases the capacitance.