The anode accelerates the electron beam along the tube and also focuses the electron beam by means of the potential divider R2. (ii) it refocuses the electron beam so that the beam emerges from the hole as a narrow beam.Īnodes A1 and A2:- These are held at a positive potential relative to the cathode. It is held at variable negative potential relative to the cathode by means of the potential divider R1, The grid serves two purposes namely: (i) as a brightness control The grid, G:- it consists of a hollow metal cylinder with a small hole at the end. Indirectly heated Cathode, C :-Emits electrons by thermionic emission. Shadow of the Maltese cross cast on the florescent screenĮvacuated Glass tube:- the glass tube evacuated to prevent scattering of the electron beam when electrons collide with air molecules. If an opaque object (Maltese cross) is placed in the path of the cathode rays, a sharp shadow of the Maltese cross is cast on the screen. Verification that electrons travel in a straight line They are electrons moving with high speeds. When cathode rays are stopped by heavy metals, x-rays are emitted. They cause fluorescence in certain materials. They are deflected by both magnetic and electric fields (this proves that they carry a charge) This shows that electrons posses momentum and therefore have mass. When the cathode rays hit the florescent screen, the screen glows. The tube is evacuated to avoid electrons interacting with any particle before they reach the screen. The thermionic emission is the process whereby metal surfaces emit electrons when heated. The electrons are produced at the cathode by thermionic emission and are accelerated towards the screen by the anode which is connected to the terminal of the extra high tension battery.
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