# Magnetic field inside a cylinder which is rotating in a non-constant angular velocity

 P: 4 1. The problem statement, all variables and given/known data A hollow cylinder of length L and radius R, is madeout of a non-conducting material, is charged with a constant surface charge $\sigma$, and is rotating, along its axis of symmetry, with an angular velocity w(t) = $\alpha$t. 2. Relevant equations 3. The attempt at a solution The answer in the manual is B = $\mu$$\alpha$tR$\sigma$ Where $\mu$ is ofcurse $\mu$ zero. [ the magnetic constant ]. The manual's solution makes perfect sense if I knew that the circular electric field which is induced by the fact that the magnetic field is changing in time is constant. because then i could say that that the displacement current density is zero. Q: How can derive that the circular electric field, induced by the changing -in-time magnetic field, is not changing with time? Thanks in advance 1. The problem statement, all variables and given/known data 2. Relevant equations 3. The attempt at a solution