A physicist wants to measure the workfunction of a metal and obtains the above g

Question

A physicist wants to measure the workfunction of a metal and obtains the above graph of the maximum kinetic energy of the emitted electrons versus the frequency of the absorbed light.

Q1:What is the workfunction?

Q2:How would the graph change if a more powerful light source was used? (5 options)

The graph would have a higher slope, but start at the same minimum frequency.
The slope does not change, but the graph would be shifted toward higher frequencies.
The slope does not change, but the graph would be shifted toward lower frequencies.
The graph would have a lower slope, but start at the same minimum frequency.
No change.

Q3:She then uses another material with a workfunction of 3.1 eV. What will be the maximum kinetic energy of the emitted electrons if the light source is tuned to a wavelength of 268 nm?

Please use the graph above to calculate Q1&Q3, and answer the multiple choice question Q2.Show all work for credit.

Explanation / Answer

Q1) Work functio w = h*fo = (6.625*10^-34*750*10^12) = 4.96*10^-19 J = 4.96/1.6 = 3.1 eV

Q2) maximum KE of the elctrons depend only on the frequency of inicident photons but not on the intensity of light

hence the answer is No change.

Q3) Wo = 3.1eV

E = h*c/lamda= (6.625*10^-34*3*10^8)/(268*10^-9) = 7.41*10^-19 J = 7.41/1.6 = 4.63 eV

KEmax= E-Wo = 4.63-3.1 = 1.53 eV

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