The work function of the following metals are given: `Na = 2.75 eV, K = 2.3 eV, Mo = 4.17 eV and Ni = 5.15 eV`. Which of these metals will not cause photoelectric emission for radiation of wavelength `3300Å` from laser source placed 1m away from these matals? What happens if the laser source is brought nearer and placed 50cm away?

Explanation

Condition for photoelectric emission, `hf gt W_(0)`
or, `(hc)/(lamda) gt W_(0)`
For `lamda = 3300 Å`
`(hc)/(lamda) = (6.6 xx 10^(-34) xx 3 xx 10^(8))/(3000 xx 10^(-10))J`
`= (6.03 xx 10^(-19))/(1.6 xx 10^(-19)) eV = 3.77 eV`
`:.` Mo and Ni will not cause photoelectric emission. If the laser source is brought nearer nearer and placed 50 cm away, then also there will be no photoelectric emission from Mo and Ni, since it depends upon the frquency of the source.