16.3 CATHODE-RAY OSCILLOSCOPE (C.R.O)
The cathode- ray oscilloscope is an instrument which is used to display the magnitudes of changing electric currents or potentials (Fig. 16.4). The information is displayed on the screen of a "cathode- ray tube". This screen appears as a circular or rectangular window usually with a centimetre graph superimposed on it. For example, the picture tube in our TV set and the display terminal of most computers are cathode- ray tubes.
The cathode- ray oscilloscope (C.R.O) consists of the following components:
The Electron Gun
The electron gun consists of an electron source which is an electrically heated cathode that ejects electrons. Electron gun also has an electrode called grid G for controlling the flow of electrons in the beam. The grid is connected to a negative potential. The more negative this potential, the more electrons will be repelled from the grid and hence fewer electrons will reach the anode and the screen. The number of electrons reaching the screen determines the brightness of the screen. Hence, the negative potential of the grid can be used as a brightness control. The anode is connected to positive potential and hence is used to accelerate the electrons. The electrons are focused into a fine beam as they pass through the anode.