Einstein's equation for photoelectric effect is `E_("max") = hf - W_(0)`, where h = Planck's constant `= 6.625 xx 10^(-34) J.s, f =` frequency of light incident on metal surface, `W_(0)`= work function of metal and `E_("max")`= maximum kinetic energy of the emitted photoelectrons.
It is evident that if the frequency f is less than a minimum value `f_(0)` or if the wavelength `lamda` is greater than a maximum value `lamda_(0)`, the value of `E_("max")` would be negative, which is impossible. Thus for a particular metal surface `f_(0)` is the threshold frequency and `lamda_(0)` is the threshold wavelength for photoelectric emssion to take place. Again if the collector plate is ketp at a negative potential with respect to the emitter plate, the velocity of the photoelectrons would decrease. The minimum potential for which the velocity of the speediest electron becoes zero, is known as the stopping potential, the photoelectric effect stops for a potential lower than this.
[velocity of light `= 3xx 10^(8) m.s^(-1)`, mass of an electron `m = 9.1 xx 10^(-31) kg`, charge of an electron, `e = 1.6 xx 10^(-19)C`
The threshold wavelength of photoelectric effect for a metal surface is `4600 Å`. Work function of the metal (in eV) is

Options

A. `2.7`
B. `3.45`
C. `4.2`
D. `6.9`

Answer

A