Ans. CATHODE-RAY OSCILLOSCOPE (CRO)
The cathode-ray oscilloscope is an instrument which is sued to display the magnitude of changing electronic currents or potential.
Working of Different Parts of Cathode-Ray Oscilloscope
The cathode-ray oscilloscope consists of the following parts:
1. The electron gun
2. The deflecting plates
3. A fluorescent screen
The Electron Gun
An electron gun produces a beam of fast moving electrons called cathode-rays.
The electrons 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 light. Hence the negative potential of the grid can be used as a brightness control. The anode is connected to the positive potential and hence is used to accelerate the electrons. The electrons are focused into a fine beam as they pass through the anode.
The Deflecting Plates
After leaving the electron gun, the electron beam passes between a pair of horizontal plates. A potential difference applied between these plates deflects the beam in vertical plane. This pair of plates provides the Y-axis or vertical movement of the spot on the screen. A pair of vertical plates provides the X-axis or horizontal movement of the spot on the screen.
The Fluorescent Screen
The screen of a cathode-ray tube consists of a thin layer of phosphor, which is a material that gives light as a result of bombardment by fast moving electrons.