An infinitely long hollow cylinder of radius `R` carrying a surface charge density `s` is rotated about its cylindrical axis with a constant angular speed `w`. The magnitude of the surface current is: [GATE 2005]

 Problem: An infinitely long hollow cylinder of radius `R` carrying a surface charge density `s` is rotated about its cylindrical axis with a constant angular speed `w`. The magnitude of the surface current is: [GATE 2005]

✅ (A)`sigmaRomega`    (B)`2sigmaRomega`    (C)`pisigmaRomega`    (D) `2pisigmaRomega`

Answer:

The surface charge density is `sigma`

The surface current density 

`vecK=sigmavecv`

or, `vecK=sigma(vecomegaxxvecR)`

or, `vecK=sigmaomegaRhatphi`

Option A is correct.