The work function for a metal is `40 eV`. To emit photo electrons of zero velocity from the surface of the metal the wavelength of incident light should be `x nm`.

Answer

31

Explanation

`W_(0)+K=hv`
`4xx1.6xx10^(-19)=(6.62xx10^(-34)xx3xx10^(8))/(lambda)`
`lambda=3.18xx10^(-7)=31xx10^(-8) m`
`lambda=31 nm`