In an oscilloscope, the horizontal deflecting plates receive a sawtooth voltage wave-form. This causes the beam to scan or sweep at a precise, adjustable speed across thescreen from left to right as seen from the outside. After each timed left- to-right sweep,the beam jumps instantly back to the left side of the screen for the next sweep.The vertical deflecting plates receive the waveform to be analyzed. This waveformmakes the electron beam undulate up and down. The combination of vertical and hori-zontal motions results in the display of the input waveform as a function of time. This isa time-domain display.Oscilloscopes can be adapted to show phenomena as a function having some do-main other than time. An example is a spectrum analyzer, showing signal amplitude asa function of frequency: a frequency-domain display. A radar set shows the distanceand direction of signal echoes from objects in the sky or in space; these are position-do-main or location-domain renditions.Electromagnetic deflectionCoils can be used instead of charged plates for deflection of the electron beam in a CRT.When currents pass through the coils, the beam changes direction at right angles to themagnetic lines of flux. The greater the current in a deflecting coil, the stronger the mag-netic field, and the greater the extent to which the beam is deflected. This is an elec-tromagnetic CRT.You can use Fig. 29-7 to imagine the workings of an electromagnetic CRT, just bythinking of coils outside the neck of the tube, rather than deflection plates inside thetube. There are two coils, one for horizontal deflection and the other for vertical de-flection.Video camera tubesVideo cameras use a form of electron tube that converts visible light into varying elec-tric currents. The two most common types of camera tube are the vidicon and the im-age orthicon.Video camera tubes54729-7Simplified cutaway view of an electrostatic CRT.