Question

The work function for tungsten and sodium are 4.5 eV and 2.3 eV respectively. If the threshold wavelength
for sodium is 5460 °A, the value of wavelength for tungsten is
(1) 5893 Å
(2) 10683 Å
(3) 2791 A
(4) 528 Å​

Answer 1

Answer:

The energy of the emitted electrons is E = h f - W

where f is the frequency and W is the work function

At the threshold E = 0   and f = W / h  

or c / y = W / h  where y is the wavelength where f = c / y

So y = c h / W

yt / ys = Ws / Wt = 2.3 / 4.5 = .511

and yt = .511 * 5460 = 2791 Angstroms