The inner and outer electrodes of a diode are coaxial cylinders of radii a = 0.6 m and b = 30 mm, respectively. The inner electrode is maintained at 70 V while the outer electrode is grounded,
(a) Assuming that the length of the electrodes ℓ >> a, b and ignoring the effects of space charge, calculate the potential at p = 15 mm.
(b) If an electron is injected radially through a small hole in the inner electrode with velocity 107 m/s, find its velocity at p = 15mm.