Chapter 13 - Quantum Physics Flashcards
What are photons?
Tiny packets of electromagnetic radiation /energy
What is the equation for the energy of a photon?
E = Hf
Energy in photon (J) = Planck Constant (6.63 x10^-34 Js) x Frequency of the electromagnetic radiation
What is the equation for the energy of a photon in terms of wavelength?
E = hc/λ
Energy of a photon = Planck constant (6.63x10^-34) x speed of light through vacuum (3x10^8) / Wavelength
How is the energy of a photon related to wavelength?
They are inversely proportional
Higher wavelength = lower energy
What is an electronvolt?
Used because joules are too big for the quantum level
1eV = The energy transferred to or from an electron when it moves through a potential difference of 1V
What is 1eV equal to in joules and vice versa ?
1eV = 1.6 x 10^-19 joules 1J = 5.25 x 10^18 eV
How do you convert from joules to eV and vice versa?
J to eV = Divide by 1.60 x 10^-19
eV to J = Multiply by 1.6 x 10^-19
What is the equation for the energy of an electron using threshold p.d.?
At threshold p.d. the energy transferred by an electron is approximately equal to the energy of the single photon it emits
Threshold p.d. x charge on electron = Energy of emitted photon
What is the photo electric effect?
When electro magnetic radiation is incident on a metal surface, electrons are emitted
What is the gold leaf experiment?
Shows the photoelectric effect using a gold leaf electroscope
Briefly touch the top plate with the negative electrode from a power supply which charges the electroscope
Excess electrons are deposited onto the plate and stem of the electroscope
Any charge developed on the top of the plate spreads to the stem and gold leaf and because they have the same charge they repel and the leaf lift up
If a clean piece of zinc is placed in the negatively charged electroscope and UV radiation is shined on it the leaf will slowly fall back to the stem showing that the electroscope lost its negative charge because free electrons are emitted from the zinc
What are 3 key observations from the photo electric effect?
Photo electrons were only emitted if the incident radiation was above a certain frequency (threshold)
If the incident radiation was above the threshold frequency then the emission of photoelectrons was instantaneous
Increasing intensity of the radiation did not increase the maximum kinetic energy of the photoelectrons, instead more electrons were emitted. Only way to increase maximum kinetic energy was to increase the frequency of the incident radiation
