Visible light cannot eject photo electrons from copper metal, whose work function is 4.4 e V. Why? Prove it mathematically.

Explanation

Work function = `lambda_0 = 4:4 eV= 4.4 xx 1.6 xx 10^(-19) J`
`(hc)/(lambda_0) = 4.4 xx 1.6 xx 10^(-19)`
`lambda_0 = (hc)/(4.4 xx 1.6 xx 10^(-19))`
`= (6.62 xx 10^(-34) xx 3 xx 10^8)/(4.4 xx 1.6 xx 10^(-19))`
`= (19.86)/(7.04) xx 10^(-34 + 8 + 19)`
`= 2.821 xx 10^(-7)`
`= 2821 xx 10^(-10)m`
`lambda = 2821 Å`
As wavelength of visible light is more than `lambda_0`, so visible light can not emit photoelectrons from copper surface.