A) We want to find the maximum kinetic energy of the photoelectrons.
E = 1243/λ - Φ
E = kinetic energy of photoelectrons, λ = light wavelength, Φ = work function
Given values:
λ = 500nm, Φ = 1.5eV
Plug in and solve for E:
E = 1243/500 - 1.5
E = 0.986eV
B) We want to find the maximum speed of the photoelectrons.
KE = 0.5mv²
KE = max kinetic energy, m = electron mass, v = max speed
Given values:
KE = 0.986eV = 1.58×10⁻¹⁹J, m = 9.11×10⁻³¹kg
Plug in and solve for v:
1.58×10⁻¹⁹ = 0.5(9.11×10⁻³¹)v²
v = 5.89×10⁵m/s
C) We want to find the stopping potential for the photoelectrons:
Vq = E
V = stopping potential, q = electron charge, E = max kinetic energy of photoelectrons
Given values:
q = e (elementary charge), E = 0.986eV
There isn't much work to do to find V. The energy E is already given in electron-volts which is defined as the amount of energy an electron gains when passed through a 1V potential difference. All you have to do is remove the "e" from "eV" and you'll have your answer.
V = 0.986V
