The cathode ray oscilloscope consists of the following components:
the electron gun;
the deflecting plates;
a fluorescent screen.
The electron gun: the electron gun is the same as the basic electron gun but with a grid, which is connected to a negative potential. The greater the negativity the more electrons that would be repelled from the grid and fewer electrons that will reach the anode and the screen. The brightness of the light is determined by the number of electrons that reach the scree, which makes the negative potential of the grid a control for brightness. The anode at the positive potential accelerates the electrons and the electrons are focused to a fine beam as they pass through an anode.
The deflecting plates: two pairs of plates are placed in the C.R.O. Voltages that are applied deflect the electron beam. The Y-plates will cause a vertical deflection and the X-plates will cause a horizontal deflection.
The fluorescent screen: the screen is coated with a fluorescent salt e.g. zinc sulphide which causes a flash of light when the electrons hot the screen.
The C.R.O.
The time base: switching on a time base applies a saw tooth voltage to the Y-plates. The saw tooth voltage makes the electron beam sweep across the screen at a constant speed. In each cycle the electron beam would be moved from the extreme left to the extreme right. Knowing the cycle period, the speed of the sweeping beam is found. Therefore, the time base is measure of time for the oscilloscope.
Measuring Voltages: through the Y-input terminals, the voltage to be measured is applied to the Y-plates. The time base is switched off. An electric field is set up when between the plates a voltage is applied. The gain of the Y-input determines the sensitivity of the oscilloscope. E.g. a gain of 0.5/div means 1.5 volts creates a deflection of 3 divisions.
Displaying Voltage Waveforms: when the time base is switched on a suitable frequency is selected for it, the voltage waveform can be displayed by the C.R.O. The input at the Yterminals is the voltage waveform.
Short intervals of time: the C.R.O. with the time base on can be used to measure short intervals of time. E.g. the time taken for sound to travel a certain distance. By finding the time taken and the distance travelled, the speed of sound can be calculated.