The work function of a substance is 4.0 eV. The longest wavelength of light that can cause photoelectron emission from this substance is approximately:

Options

A. `540 nm`
B. `400 nm`
C. `310 nm`
D. `220 nm`

Answer

C

Explanation

`W_(0)=4eV, lambda_("max")=?, W_(0)=(hc)/lambda_("max")`
`4eV=1240/lambda_("max") nm-eV [ :' hc=1240 nm-eV]`
`lambda_("max")=310 nm`.