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

Question

he 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 electrical current. The heat (energy) is transferred to the 'free' electrons of the metal which allow some electrons to escape from the surface. After a short period of operation the filament has lost enough electrons to give it an overall charge of 9.50 × 10-7 C. How many electrons, ne, has the filament lost? If the filament is 2.45 g of tungsten, what fraction of electrons, ef, 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 × 1023 1/mol.)


ne=?

ef=?

Explanation / Answer

ne = 9.5E-7/1.6E-19=5.94E12

total e = 2.45/(183.8)*74*6.02E23

ef= 5.94E12/(2.45/(183.8)*74*6.02E23)=1.0E-11

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