A photoelectric source is illuminated successively by monochromatic light of wavelenth `lamda and (lamda)/(2)`. Calculate the work function of material of the source if the maximum kinetic energy of the emitted photoelectrons in the second case is 3 times that in the first case.

Explanation

We know kinetic energy of emitted photoelectrons,
`K = hf - W_(0) = (hc)/(lamda) - W_(0)`
In the first case,
`K_(1) = (hc)/(lamda_(1)) - W_(0) = (hc)/(lamda) - W_(0)`
In the second case,
`K_(2) = (hc)/(lamda_(2)) - W_(0) = (2hc)/(lamda) - W_(0)`
It is given that, `K_(2) = 3K_(1)`
or, `(2hc)/(lamda) - W_(0) = 3 ((hc)/(lamda) - W_(0)) or, 2W_(0) = (hc)/(lamda)`
`:. W_(0) = (hc)/(2lamda)`