Question

Work function of certain metals are listed below.the no. of metals which will show photoelectric effect when light of 300nm wavelength falls on the metal is ____ (integer)
metal work function (eV)
li 2.4
Na 2.3
k 2.2
Mg 3.7
Cu 4.8
Ag 4.3
Fe 4.7
Pt 6.3
W 4.75

Answer 1

The energy of radiation must be equal to or greater than the work functions of metals to show photoelectric effect. We need to convert wavelength of radiation into energy expressed in eV units. Eradiation = hc/λ = 6.626 x 10-34 J s x 3.0 x 108 m s-1/300 x 10-9 m = 6.626 x 10-19 J Now convert this value into eV. We know that: 1 J = 6.24 × 1018 eV Therefore: 6.626 x 10-19 J = 6.626 x 10-19 x 6.24 × 1018 eV = 4.134 eV Conclusion: Since the work functions of only Li, Na, K and Mg fall below 4.134 eV, only these metals can show photoelectric effect upon exposure of radiation of 300nm wavelength. The number of metals that can show photoelectric effect = 4.