Question

17. It takes 254 kJ/mol to eject electrons from a certain metal surface. What is the longest wavelength of light (nm) that can be used to eject electrons from the surface of this metal via the photoelectric effect 18. Why does this question ask you about the 'longest wavelength of radiation, rather than the 'shortest'? 19. When radiation of wavelength 2.45 x 10'm falls on a metal surface, the maximum kinetic energy of the emitted electrons is found to be 6.73x10"). What is the value in )) of the work function of the metal? a. 2.64x10-17 b. 1.49x10-19 C. 1.38x10-19 d. 1.83x1017 e. 8.11x1019

Answer 1

17 Ans EneayE 2 54 kmol Energy of Pho ten is given by (h Plank's Constan = hc E = ve locity of light= 3x1 msec wave length dahc E .62X1 3x10 -34 d= 2 su x 10 da7.2x 31 -31 max. Wavelengtn 7.8x 13 's the Here the iven Vaue of Ene amount of encus euyed to emut an minimumn etec Photen frem mcai suutace Mence hene the wave leng t euivedfer this minimum enugyis Calied Threshid wave ieng t wlich s maximum

Answer 2

E = (254 kJ x 10³J/mol)/(6.022 x 10²³ electron/mol) = 4.218 x 10^-19 J/electron

λ = hc/E = (6.626 x 10^-34J.s) x (3 X 10⁸m/s)/(4.218 x 10^-19J/ele) = 4.71 x 10^-7m

λ = 471 nm per photon, under the assumption that each phonton will cause the electron to overcome the workfunction of the metal and get ejected.