# THE CATHODE-RAY TUBE

THE CATHODE-RAY TUBE

of potential is applied to an important class of devices or “CRTs” for short. Cathode-ray tubes are found in used in TV picture tubes and computer displays. The  early 1900s. Cathode-ray tubes use an electron beam; before the was understood, it was called a cathode ray because it emanated of a vacuum tube diagram of the principal elements of a cathode-ray tube. is a very good vacuum, with a pressure of around 0.01 Pa greater pressure, collisions of electrons with air molecules beam excessively.

The cathode, at the left end in the figure, the heater, and electrons evaporate from the surface of , with a small hole at its center, is maintained at of the order of 1 to 20 kY, relative to the cathode. This potent an electric field directed from right to left in the region anode and the cathode. Electrons passing through the hole in beam and travel with constant horizontal velocity from the screen. The area where the electrons strike the screen glows the number of electrons that reach the anode and hence on the screen. The focusing anode ensures that electric leaving the cathode in slightly different directions are focused d and all arrive at the same spot on the screen. We won’t need to  grid or focusing anode in the following analysis. The assembly of focusing anode, and accelerating electrode is called the electron The am of electrons passes between two pairs of deflecting between the first pair of plates deflects the electrons horizontally between the second pair deflects them vertically. If no deflecting electrons travel in a straight line from the hole in the accelerating the screen, where they produce a bright spot. To analyze the electron motion, let’s first calculate the speed they leave the electron gun.

We can use the same method as in The initial speeds at which the electrons are emitted small in comparison to their final speeds, so we assume that the Then the speed v, of the electrons as they leave the electron gun The kinetic energy of an electron leaving the anode depends reference between anode and cathode, not on the details of trajectories within the electron gun.If there is no electric field between the horizontal enter the region between the vertical-deflection plates (shown If there is a potential difference (voltage) V2 between plate at higher potential, there is a downward electric field between the plates.

A constant upward force with magnitude trons, and their upward (y-component) acceleration is The horizontal component of velocity v, is constant. region between the plates is a parabolic trajectory, just as . 22-6) and in projectile motion (Section 3-4); in all of these constant x-velocity and constant y-acceleration. After the region, their paths again become straight lines, and they y above its center. We are going to prove that this to the deflecting potential difference V2 monitors operate on the same principle, using a magnetically trace out images on a fluorescent screen. In this context the play or a VDT (video display terminal).