24. Electric Force & Field; Gauss' Law

The electric field at a point in space is E =(400î+100jˆ)N/C.a. What is the electric force on a proton at this point? Give your answer in component form.

An infinitely wide, horizontal metal plate lies above a horizontal infinite sheet of charge with surface charge density 800 nC/m². The bottom surface of the plate has surface charge density -100 nC/m² . What is the surface charge density on the top surface of the plate?

A spark occurs at the tip of a metal needle if the electric field strength exceeds 3.0 x 10⁶ N/C, the field strength at which air breaks down. What is the minimum surface charge density for producing a spark?