Question

In an experiment of the photoelectric effect, the graph of maximum kinetic energy E_K of the emitted photoelectrons versus the frequency v of the incident light is a straight line AB shown in Figure 6 below:

Find:

1) Threshold frequency of the metal

2) The work function of the metal.

3) Stopping potential for the photoelectrons emitted by the light of frequency `v = 30 xx 10^14 Hz`

Answer 1

1) From the graph,

Threshold frequency = `10 xx 10^14 Hz`

`v_0 = 10^15 Hz`

2) The work function of the metal

`w = hv_0`

`= 6.63 xx 10^(-34) xx 15^15`

`= (6.63  xx 10^(-19))/(1.6 xx 10^(-19))`

= 4.14 eV

3) `E_k = 8 eV`

Stopping potential = `K.E._"max" - phi`

`=> 8 - 4.14 = 3.86 eV`

`V = 3.86/e xx ev = 3.86 V`