The concept of thermionic emission is the basis of modern X-ray tubes, which are

Question

The concept of thermionic emission is the basis of modern X-ray tubes, which are the workhorse of a medical X-ray image In this process a filament (a piece of metal in a vacuum) is heated by the application of ctoctnc.il current The heat (energy) is transferred to the free' electrons of the metal which allow some electrons lo escape from the surface. After a short period of operation the filament has lost enough electrons lo give it an overall charge of 1.100 times 10-6 How many electrons. nc,. has the filament lost? If the filament is 2 00 g of tungsten, what fraction of electrons, e , does this represent? (HINT: The atomic number of tungsten is 74.0. the atomic weight is 183 8 g/mol and Avogadro's constant = 6.02 times 1023 1/mol.)

Explanation / Answer

No. of electrones* 1.6*10^-19 = Total charge => No. of e = 1.1*10^-6/ 1.6*10^-19 = 6.875*10^12. Moles of tungsten = mass/Mol. wt. = 2/183.8 = 0.01088 mol atoms of tungsten = Avogadros conatant* 0.01088 = 0.0654976*10^23 Total No. of electrones = Atomic no. * Atoms = 4.8468*10^23 Fraction = Answer of part 1 / Total = 1.41846*10^-11.

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