# Electricity and magnetism

good afternoon, these are my problems, I already tried to solve them but my anwers isnt well:

1-the electrical potential at certain distance of a charge of 600 V. and the electrical field is 200 N/C. At what distance of this charge is it necessary to place a charge of 0.1x10 ^-6 C and the opposite sign for that the potential in the same point is null?

2-three charge q1 = 1.5x10 ^-3 C, q2 = 0.5x10 ^-3 C and q2 = 0.2x10 ^-3 C are distributed in a plane, forming a triangle. The straight line that it joins q1 with q3 measures 1 m, the straight line that it joins q2 with q3 measures 0.5 m and the angle that both straight lines form is 30 °. Which is the potential entire energy of the system?

3-Two metallic big and parallel badges are placed at a distance of 0.5 cm between both. if between them there gets connected a source of electrical energy which difference of electrical potential is 90 V.: Which will be the charge for unit of area in the surface of the badges?

thnks for att.