Chapter 13 - Quantum Physics Flashcards
Describe the photon model of EM radiation.
EM radiation comes in discrete packets of energy known as photons.
What is a photon?
The particulate nature of EM radiation.
Define one electronvolt (1eV).
The kinetic energy gained by an electron when it is accelerated through a PD of 1 volt.
Outline an experiment that could be used to determine the Planck constant.
-Set up circuit with LED of known wavelength.
-Ensure P.D. across LED is threshold P.D.
-Plot graph of P.D. against ⅟λ.
-Gradient = hc/e
What is the threshold P.D.?
The minimum P.D. required to turn on an LED.
Outline the photoelectric effect.
High-frequency radiation on the surface of a metal causes electrons to be emitted.
How does a gold leaf electroscope work?
-Charge developed at the connected metal plate spreads to the leaf & stem.
-When charged with excess electrons, the gold leaf is repelled and moves away from the stem.
What is the threshold frequency?
The minimum frequency of EM radiation required to release electrons from a certain metal.
What happens when incident radiation on a metal plate is above the threshold frequency?
-Emission of photoelectrons is instantaneous.
-Maximum kinetic energy of photoelectrons does not change.
How do you increase the maximum kinetic energy of photoelectrons?
Increase the frequency of incident radiation.
What happens when a negatively charged zinc plate connected to a gold leaf electroscope is exposed to high-frequency radiation?
-Electrons are emitted from the plate.
-Gold leaf droops down, getting closer to the stem.
Explain the photoelectric effect using the photon model.
-Each electron requires a certain amount of energy to escape from a metal.
-Each photon can transfer its energy to an electron in a one-to-one interaction.
Explain what effect intensity (photons per second) has on emitted electrons.
Because it is a one-to-one interaction, intensity does not have any effect on photoelectrons released.
Define work function (Φ).
The minimum energy required to release an electron from the surface of a metal.
Explain what effect increasing intensity has on the emission of photoelectrons.
-Greater intensity = more photons
-More photons interact with more electrons, meaning more photoelectrons are released.
When an electron absorbs a high energy photon and is released from a metal, where does the remaining energy go?
Kinetic energy of the electron.
Why is electron diffraction possible?
Under some circumstances, moving electrons show characteristics of waves, meaning they can diffract when moving through a very small gap.
What is the de Broglie equation used for?
To determine the wavelength of a particle of a given momentum.
