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Wavelength/kinetic energy/threshold frequency question?? Please show steps?
In studying a solid material for possible use in a solar cell (which turns light into electrical energy), material engineers shine a monochromatic blue light (λ = 420 nm) to produce photoelectrons. They measure the maximum kinetic energy of the emitted electrons to be 1.00 x 10-19J. Predict what will happen when the engineers test the material with red light (λ = 700 nm). Will the light dislodge electrons from the material? If so, how much kinetic energy will those dislodged electrons have?
1 Answer
- Old Science GuyLv 74 years ago
...
find E of 420nm photon
E = h f
but c = f L so f = c/L
E = h c/L = 6.626E-34 (3.00E8) / (420E-9) = 4.733E-19 J
find work function of atom
W = Ephoton - Eelectron = 4.733E-19 - 1.00E=19 = 3.73E-19
now, will E of 700nm photon exceed W?
E = h c/L = 6.626E-34 (3.00E8) / (700E-9) = 2.84E-19 J
this is less than the work function
so
no photoelectrons will be emitted
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