Radiation of frequency `10^(15)Hz` is incident on two photosensitive surface P and Q. There is no photosensitive from surface P. Photoemission occurs from surface Q but photoelectrons have zero kinetic energy. Explain these observations and find the value of work function for surface Q.

Explanation

There is no photoemissin from surface P because the frequency of incident radiation is less than its threshold frequency.
Since photoemission occurs from surface Q and the photoelectrons have zero kinetic energy, then the frequency of incident radiation is equal to the threshold frequency for surface Q.
Work function for surface Q, `W_(Q) = hf`
`6.6 xx 10^(-34) xx 10^(15) = 6.6 xx 10^(-19) J = 4.125 eV`