Light of wavelength 400 nm illuminates a potassium electrode (work function 2.3 eV)
What is the photon energy?
E photon λ = 3.1 eV
What is the energy of the emitted electron?
3.1 eV – 2.3 eV = 0.8 eV
What is the stopping potential?
Ocean water is most transparent at wavelengths of 470 nm, so bioluminescent creatures emit
light at approximately this wavelength. Firefly squid use ATP to provide the energy for this
reaction. Metabolizing one molecule of ATP releases 0.32 eV. How many molecules of ATP
must be metabolized to produce one photon of blue light at 470 nm?
E photon = = 2.6 eV
0.32eV = 8.15
9 molecules of ATP
Electrons are accelerated from rest through an 8000 V potential difference. By what factor
would their de Broglie wavelength increase if they were instead accelerated through a 2000 V
K = Δ Ue
K = ½ mv 2
λ = p = mv
ΔU ↓ 4
K ↓ 4
v ↓ 2