Calculate the longest wavelength of incident light on platinum for which photo electrons are just emitted from platinum (work function for platinum `= 6.2` eV).

Explanation

Given, `w = 6.2" eV" = 6.2xx 1.6 xx 10 ^(-19)" J, " lambda_("max") = ?`
`w = hv_(0) = (hc)/lambda_(0)`
`therefore lambda_(max) = (hc)/w =(6.625xx10^(-34)xx3xx10^(8))/(6.2xx1.6xx10^(-19))=2.003xx10^(-7) = 2000` Å.