A dipole of moment p is placed in a uniform field E. The work done in rotating it from stable equilibrium to unstable equilibrium is:

A charged particle of mass m and charge q is released from rest in a uniform electric field E. Its kinetic energy after time t is:

A charged particle enters a uniform electric field perpendicular to the field with velocity v. The time to cross a region of width d (along E) is:

Four charges +q, -q, +q, -q are placed at the four corners of a square of side a. The electric field at the center is:

A thin spherical shell of radius R has a total charge Q. A point charge q is located at distance R/2 from the center. The force on q is: