Quantum Phenomena
How is the energy of a photon related to its frequency?
Directly proportional.
formula for *energy of a photon*
E = energy of photon h = Planck's constant f = frequency c = speed of light (in vacuum) λ = wavelength
What is the *photoelectric effect*?
Electrons are emitted (there's a current) when light (of certain frequencies) shines on a metal.
What is *stopping voltage (potential)*?
Energy required to stop an electron emitted (stop the current generated from photoelectric effect).
What determines the energy of photons: the frequency or wavelength (color) or the intensity (brightness)?
Frequency or wavelength (color).
What determines the threshold energy in the photoelectric effect: the frequency or wavelength (color) or the intensity (brightness)?
Frequency or wavelength (color).
What determines the *stopping voltage*: the frequency or wavelength (color) or the intensity (brightness)?
Frequency or wavelength (color). Increasing frequency increases the energy of emitted electrons, which increases voltage required to stop them.
What is a *photon*?
A packet of energy, a particle of light (the smallest unit of light).
If all moving particles have a de Broglie wavelength, why can't we see wave behavior in everything?
Because wave behavior is much easier to observe in very small particles (like subatomic particles). The bigger the particle, the smaller the wave behavior.
If the wave model of light were enough to explain the photoelectric effect, what should happen when brighter light shines on a metal?
Brighter light (higher intensity, higher amplitude) should eject electrons with more kinetic energy, but it doesn't.
If the wave model of light were enough to explain the photoelectric effect, what should happen when dim light shines on a metal?
If dim light (low intensity) is at the threshold frequency, then it should take a long time before the electrons gain enough energy to be ejected. But in reality, as long as the threshold frequency is reached, even dim light ejects electrons almost instantaneously.
What determines the amount of *current* generated by the photoelectric effect: the frequency or wavelength (color) or the intensity (brightness)?
Intensity (brightness). Increasing intensity increases the number of emitted electrons, which increases current.
How is the energy of a photon related to its wavelength?
Inversely proportional.
How is the momentum of a photon or a moving mass related to its wavelength?
Inversely proportional.
What is the *Heisenberg uncertainty principle*?
It is impossible to know both the momentum and the position of a particle at the same time. The more accurately you measure one thing (like the speed), the less accurately you can measure the other thing (like the position).
formula for *maximum kinetic energy of ejected electron* (photoelectric effect)
K = maximum kinetic energy of ejected electron E = hf, energy of photon absorbed by metal ∅ = work function of metal
What does *quantized* mean?
Something can exist only at certain definite values, and not in-between values (like steps instead of a ramp).
The same monochromatic light generates a current in metal 1 but not in metal 2. Which metal has the higher work function?
Metal 2. Higher work function means a higher threshold frequency needs to be reached in order to eject an electron.
A higher-wattage bulb emits the same color of light as a lower-wattage bulb. Which bulb emits photons of higher energy?
Neither because they both emit the same frequency of light. Energy of photons depends on frequency or wavelength, not intensity (brightness).
Does a photon exist as an object at rest?
No.
Does a photon have mass?
No.
Does changing the *brightness* of light that shines on a metal affect the energy of the emitted electrons?
No. Increasing intensity (brightness) increases the number of ejected electrons (the current), but the energy of those electrons remains the same if the frequency of light is the same.
Does an electron that receives the minimum energy needed to be ejected have any kinetic energy?
No. It received just enough energy to be ejected - it received energy in the amount of the work function, so the kinetic energy is zero.
What does the *slope* of a maximum kinetic energy and frequency graph represent?
Planck's constant (h).
What is the significance of the *photoelectric effect*?
Provides experimental evidence that light behaves like a particle (is made of discrete units called photons).
What happens to the maximum radiation intensity as temperature increases: shifts to shorter wavelengths (higher frequency) or longer wavelengths (lower frequency)?
Shift toward shorter wavelengths (higher frequency).
What is the *de Broglie wavelength*?
The idea that since light waves display particle behavior, particles should display wave behavior. And so all moving matter should have a wavelength associated with it.
What is the *work function* of a metal?
The minimum energy needed to eject an electron from the metal.
How is the *threshold frequency* represented on a graph of maximum kinetic energy and frequency?
The x-intercept. The linear graph is shifted to the right of the origin. The graph starts at the threshold frequency.
How is the *work function* (∅) represented on a graph of maximum kinetic energy and frequency?
The y-intercept when the graph is extrapolated to the left.
What is the *wave-particle duality*?
Waves can act like particles, and particles can act like waves.
Does changing the *color* of light that shines on a metal affect the energy of the emitted electrons?
Yes. Increasing the frequency of light increases the energy of the photons hitting the metal, which increases the energy of the ejected electrons.
formula for *stopping voltage* (photoelectric effect)
eV = stopping potential (voltage) K = maximum kinetic energy of ejected electron hf = energy of absorbed photon ∅ = work function of metal
formula for *momentum of a photon*
p = momentum of photon h = Planck's constant λ = wavelength
formula for *de Broglie wavelength*
λ = wavelength h = Planck's constant p = momentum of photon