What frequency should the light be directed to the surface of lithium so that the maximum speed of photoelectrons

| April 10, 2021 | education

What frequency should the light be directed to the surface of lithium so that the maximum speed of photoelectrons is 2.5 • 10 ^ 6 m / s? The work function of electrons from lithium is 2.39 eV.

V = 2.5 * 10 ^ 6 m / s.
Aout = 2.39 eV = 3.83 * 10-19 ^ J.
h = 6.6 * 10 ^ -34 J * s.
m = 9.1 * 10 ^ -31 kg.
v -?
Under the influence of photons of light, electrons are pulled out from the surface of metals and a certain speed is imparted to them.
Let us write down the equation of the photoelectric effect: h * v = Aout + m * V ^ 2/2, where h is Planck’s constant, v is the frequency of incident photons, Aout is the work function of the metal, m is the electron mass, V is the electron velocity.
v = (Aout + m * V ^ 2/2) / h.
v = (3.83 * 10-19 ^ J + 9.1 * 10 ^ -31 kg * (2.5 * 10 ^ 6 m / s) ^ 2/2) / 6.6 * 10 ^ -34 J * c = 4.88 * 10 ^ 15 Hz.
Answer: the frequency of light is v = 4.88 * 10 ^ 15 Hz.



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