An Electron in a Diode Before the advent of solid-state electronics, vacuum tube

Question

An Electron in a Diode

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. (Figure 1)

Part A

Suppose a diode consists of a cylindrical cathode with a radius of 6.200×102 cm , mounted coaxially within a cylindrical anode with a radius of 0.5580 cm . The potential difference between the anode and cathode is 360 V . An electron leaves the surface of the cathode with zero initial speed (vinitial=0). Find its speed vfinal when it strikes the anode.

Express your answer numerically in meters per second.

m/s

Explanation / Answer

energy gained due to electric potential is equivalent to kinetic energy

KE = qV
KE = 1.602 * 10-19 * 360
KE = 5.767 * 10-17

1/2 mv2 = 5.767*10-17

mv^2 = 1.153*10-16
9.11 * 10-31 * v^2 = 1.153*10-16
v^2 = 1.266*1014
v =1.125*107 m/s

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