Light with a wavelength of 355 nm illuminates a metal cathode. The maximum kinet

Question

Light with a wavelength of 355 nm illuminates a metal cathode. The maximum kinetic energy of the emitted electrons is 0.81 eV . What is the longest wavelength of light that will cause electrons to be emitted from this cathode?
Light with a wavelength of 355 nm illuminates a metal cathode. The maximum kinetic energy of the emitted electrons is 0.81 eV . What is the longest wavelength of light that will cause electrons to be emitted from this cathode?
What is the longest wavelength of light that will cause electrons to be emitted from this cathode?

Explanation / Answer

Convert the kinetic energy K = 0.81eV to joules =1.29776e-19
Find the photon energy E in joules at 375nm using E=hc/ =6.62 x 10^-34*3*10^8/(375*10^-9) =5.286*10^-19 j
If the work function is W then
E = W + K

Calculate W: W = E - K. = 3.986224*10^-19

The longest wavelength of light, ', that will cause electrons to be emitted from this cathode has photon energy E' = hc/' where E' = W

' = hc/W =6.62 x 10^-34*3*10^8/(3.986224*10^-19) =4.9821*10^-7 m

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