Question

# Steel and iron are often "galvanized" or coated with a thin layer of zinc metal to...

Steel and iron are often "galvanized" or coated with a thin layer of zinc metal to prevent corrosion (iron rusts but zinc does not). What is the longest wavelength of light (in nm) that can eject electron from zinc metal? (i.e. assume the electrons kinetic energy is very close to zero.) The work function of zinc = 4.3 eV and 1 electron- volt (eV) = 1.602 x 10 ^ -19 J.

Solution :-

Work function of the zinc is 4.3 eV

Lets convert it to joules

4.3 eV* 1.602*10^-19 J / 1 eV = 6.8886 *10^-19 J

Now using this energy we can calculate the wavelength of the light that can eject the electron from the surface of the zinc

E= hc/l

E= energy , h= planks constant , c= speed of light , l = wavelength

6.8886*10^-19 J = 6.626*10^-34 J.s * 3*10^8 m per s / l

(6.626*10^-34 J.s * 3*10^8 m per s)/ 6.8886*10^-19 J = l

2.89*10^-7 m = l

Now lets convert meter to nm

2.89*10^-7 m * 1*10^9 nm / 1 m = 289 nm

So the longest wavelength that can eject the electron from the surface of the zinc is 289 nm

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