When the potential difference between the plates of an ideal air‐filled parallel plate capacitor is 35 v, the electric field between the plates has a strength of 750 v/m. if the plate area is 4.0 × 10-2 m2, what is the capacitance of this capacitor?

iron would move it is magnetic there is a mag field around the current in the wire

the box does not move because you need to use a force greater than 300 n. you are only using 50 n. it needs to at least be 301 n for the box to move because then it is an unbalanced force and it will move the way that the greater force is pushing it. if you use only 300 n it will be a balanced force and will not move because the force you are exerting on the   box is the same as its force.

hope this !

im sorry if i went too in depth, i am going to include a link to a video on khan academy that will explain this.   hope that you like the video and that it explains more in detail to you.

that is the link.