Question 2602
{"accessible":false,"alternatives":[{"id":12769,"text":"can be machined into a thin wire"},{"id":12770,"text":"has a high atomic number"},{"id":12771,"text":"has a high melting point"},{"id":12772,"text":"has a low electrical resistance"},{"id":12773,"text":"produces free electrons through thermionic emission"}],"archived":false,"correctAlternativeId":12772,"explanation":"\u003cp\u003eThe tungsten filament is ideal for producing free electrons via the process of thermionic emission due to the following properties:\u003c/p\u003e\u003cul\u003e\n\u003cli\u003e\u003cp\u003eHas a high atomic number and therefore, many valence electrons\u003c/p\u003e\u003c/li\u003e\n\u003cli\u003e\u003cp\u003eHas a high melting point. The high electrical resistance in the wire causes the filament to reach extremely high temperatures (which provides the energy required for excitation of the valence electrons). \u003c/p\u003e\u003c/li\u003e\n\u003cli\u003e\u003cp\u003eCan be machined into a thin wire whilst maintaining structural integrity. This increases the surface area allowing more area for thermionic emission to occur. \u003c/p\u003e\u003c/li\u003e\n\u003c/ul\u003e\u003cp\u003eImportantly, the electrons at the surface of the filament will remain there unless a tube potential is applied. Thermionic emission makes electrons available at the filament surface but is not responsible for the acceleration of electrons towards the anode.\u003c/p\u003e","id":2602,"imageUrl":null,"imageAttribution":null,"imageAttributionCaseInfo":null,"firstQuestionPath":"/questions/2602","nextQuestionPath":"/articles/cathode-x-ray-tube/questions/616","relatedArticles":[{"id":29685,"title":"Thermionic emission","link":"/articles/thermionic-emission?lang=gb"},{"id":79682,"title":"Focusing cup","link":"/articles/focusing-cup?lang=gb"}],"alsoUsedIn":[{"id":1551,"kind":"RestrictedPage","title":"Page 1551 (in no courses)","link":"https://radiopaedia.org/admin/restricted_pages/1551"},{"id":1995,"kind":"Course","title":"Imaging Physics: X-ray peer review - page 1995","link":"https://radiopaedia.org/courses/imaging-physics-x-ray-peer-review/pages/1995"},{"id":1995,"kind":"Course","title":"Imaging Physics: X-ray - page 1995","link":"https://radiopaedia.org/courses/imaging-physics-x-ray/pages/1995"}],"stem":"\u003cp\u003eWhich of the following is \u003cstrong\u003eNOT \u003c/strong\u003ea property of the tungsten filament coil within the cathode of the x-ray tube?\u003c/p\u003e","menuLinks":[{"text":"Report problem with question","url":"https://docs.google.com/forms/d/e/1FAIpQLSfO3soWYhOjJ7yErSysyCe5V4A1CqW7WK3rDA7MtAkecMGqNw/viewform?entry.1624461248\u0026entry.553583435=https://radiopaedia.org/questions/2602"}],"attemptsPercentages":[{"alternativeId":"12770","percentage":2},{"alternativeId":"12772","percentage":87},{"alternativeId":"12773","percentage":4},{"alternativeId":"12769","percentage":5},{"alternativeId":"12771","percentage":2}],"promptToLogin":false,"questionManager":false,"articleId":"cathode-x-ray-tube"}