Before the advent of solid-state electronics, vacuum tubes were widely used in r

Question

Before the advent of solid-state electronics, vacuum tubes were widely used in radios and other devices. A simple type of vacuum tube known as a diode consists essentially of two electrodes within a highly evacuated enclosure. One electrode, the cathode, is maintained at a high temperature and emits electrons from its surface. A potential difference of a few hundred volts is maintained between the cathode and the other electrode, known as the anode, with the anode at the higher potential.

Suppose a diode consists of a cylindrical cathode with a radius of 6.200*10^-2 cm, mounted coaxially within a cylindrical anode with a radius of 0.5580 cm. The potential difference between the anode and cathode is 380V. An electron leaves the surface of the cathode with zero intial speed ((v)initial = 0). Find its speed Vfinal when it strikes the anode.

Explanation / Answer

the work done on the electron W = dV*q

initial velocity vi = 0

initial KE = KEi = 0.5*m*vi^2 = 0

final KE = KEf = 0.5*m*vf^2

from work energy theorem Work done = change in KE

W = KEf = 0.5*m*vf^2

therefore

dV*q = 0.5*m*Vf^2

vf = sqrt(2*KE/m)

vf = sqrt((2*dV*q)/m)

vf = sqrt((2*380*1.6*10^-19)/(9.11*10^-31)

vf = 1.16*10^7 m/s <-------answer

Related Questions

Navigate

• Browse (All)
• Browse B
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.