Examination 7

Please answer all questions True or False. There is no negative marking. 1. The cathode of the X-ray tube a. Is commonly made of tungsten b. Has a high melting point c. Has a low resistance d. Is positively charged in relation to the anode e. Can exceed temperatures of 2200°C The cathode of a typical X-ray tube is commonly made of a coiled wire of tungsten. This metal is chosen because it has a high melting point and low vapour pressure (few electrons are evaporated off the surface). The process of producing electrons is called Thermionic Emission. Tungsten has a relatively high resistance and this is needed to reach the high temperatures required to achieve thermionic emission. The temperature can exceed 2200°C. The cathode is negatively charged in relation to the anode. 1a. True  – the cathode is commonly made from a coiled wire of tungsten 1b. True  – it must have a high melting point 1c. False  – the resistance needs to b...