Page 650 No2450 A thinspherical conducting shell of radius R

Page 650, No.24-50 A thin,spherical, conducting shell of radius R is mounted on an

isolating supportand charged to a potential of – 125 V. An electron is thenfired directly

toward the center ofthe shell, from point P at a distance r from the center of the shell

(r >> R). What initial speed, v0 is needed for the electron to just reach theshell before

reversing direction?

when the electron just reaches the shell before reversingdirection then the work done on the electron is

W = V * q

V = -125 V and q = -1.6 * 10^-19 C (charge on theelectron)

the work done on the electron is equal to the kinetic energyof the electron therefore we get

W = (1/2)m * v_o²

or (1/2)m * v_o² = V * q

or v_o = (2V * q/m)^1/2

m = 9.1 * 10^-31 kg

or v_o = (2 * -125 * -1.6 * 10^-19 C/9.1 *10^-31)^1/2 = 6.63 * 10⁶ m/s