  Response of a single-walled carbon nanotube to external electric field, F, is
calculated analytically within the classical electrostatics. Field-induced
charge density distribution is approximately linear along the axis of metallic
nanotube and depends rather weakly, as ln(h/r), on the nanotube length, h,
(here r is the nanotube radius). In a semiconducting nanotube with a gap, E_g,
charge separation occurs as F exceeds the threshold value F_{th}=E_g/eh. For
F>F_{th}, positively and negatively charged regions at the ends of nanotube are
separated by a neutral strip in the middle. For bent nanotubes the number of
neutral strips can be one or two depending on the direction of F.
