Chapter 13, Quantum Physics Flashcards
How is the energy of a photon of light found?
E=hf (Energy = Planck’s constant * frequency).
How can energy of a photon be found using the wavelength?
Substitute c=fλ into E=hf to give E=hc/λ (Energy = Planck’s constant * speed of light (in a vacuum)/ wavelength)
How do you convert electron volts to Joules?
Multiply by e (fundamental charge).
How can LED’s be used to determine Planck’s constant?
The threshold P.D. (when it starts emitting photons) is when the electrons have minimum energy to allow the LED to emit photons, E = Ve = hf=hc/λ (P.D. * e = Planck’s constant * c / wavelength (wavelength usually given by LED manufacture)), a graph can be plotted (V against 1/λ) with the gradient being hc/e.
What is the photoelectric effect?
Where high (enough) energy photons collides with a metal releasing electrons.
How can a gold-leaf electroscope demonstrate the photoelectric effect?
A negative charge is deposited on the metal plate raising the gold leaf, when a high (enough) energy photon beam is shone on a zinc plate on top of the electroscope, the gold leaf will go back down as the electrons escape.
How is the photoelectric effect evidence that light behaves as a photon?
Because electrons are only emitted if the frequency of the radiation is high enough regardless of the intensity of the beam (also there was no delay for high enough frequency photons and above the threshold frequency, increasing intensity did not increase K.E. of the electrons only the amount of them), this could only occur if reactions were one photon to one electron.
What happens to left over energy in the photoelectric effect above the energy required to remove an electron?
This energy must go into K.E. by the principle of conservation of energy.
What does the equation hf = ϕ +KE(max) show?
The energy of a photon (hf) is equal to the work function (ϕ min energy required to release an electron) and the maximum possible K.E. of an electron (since electrons could come from deeper within the metal the K.E. isn’t always max)
How can the work function (ϕ) of a material be found?
Plot KE(max) against frequency of photons and the y intercept is -ϕ, x intercept if f(0) (threshold frequency).
How was particle wave duality proven?
By firing electrons through a very thin sheet of graphite making a (circular) diffraction pattern.
What is the de Broglie Equation?
λ = h/p (wavelength = Planck’s constant / momentum).
