Ch. 9: Atomic and Nuclear Phenomena Flashcards
defn: photoelectric effect
when light of a sufficiently high frequency (typically, blue to ultraviolet light) is incident on a metal in a vacuum, the metal atoms emit electrons
defn: current (in context of photoelectric effect)
electrons liberated from the metal by the photoelectric effect will produce a net charge flow per unit time (current)
provided the light beam’s frequency is above the threshold frequency of the metal, light beams of greater intensity produce larger or smaller current?
larger!
if the light beam has higher intensity, what does that say about the number of photons per unit time that fall on an electrode, and the number of electrons per unit time liberated from the metal?
higher intensity light beam = greater # of photons falling on electrode = greater # electrons liberated from the metal
defn: threshold frequency (fT)
the minimum frequency of light that causes ejection of electrons
what does the threshold frequency depend on?
the type of metal being exposed to the radiation
the photoelectric effect is an “all-or-nothing” response, so what happens if the frequency of the incident photon is less than the threshold frequency?
the frequency of the incident photon is greater than the threshold frequency?
if the frequency of the incident photon is less than the threshold frequency, then no electron will be ejected because the photons do not have sufficient energy to dislodge the electron from its atom
if the frequency of the incident photon is greater than the threshold frequency, then an electron will be ejected, and the maximum kinetic energy of the ejected electron will be equal to the difference between hf and hfT (the work function)
defn: photons
an integral number of light quanta
do waves with higher frequency have shorter or longer wavelengths? higher or lower energy? what about waves with lower frequency?
what color/type of wave is each near?
HIGH FREQUENCY = short wavelengths = high energy = blue and ultraviolet end
LOW frequency = long wavelengths = low energy = red and infrared end
what happens to the electron if: the frequency of a photon of light incident on a metal is AT the threshold frequency? ABOVE the threshold frequency?
AT: electron barely escapes from the metal
ABOVE: photon has more than enough energy to eject a single electron, the excess energy will be converted to kinetic energy in the ejected electron
defn: work function
the minimum energy required to eject an electron
when is Kmax achieved?
when all possible energy from the photon is transferred to the ejected electron
func: infrared (IR) spectroscopy
used to determine chemical structure because different bonds will absorb different wavelengths of light
func: UV-Vis spectroscopy
takes IR spectroscopy one step further, looking at the absorption of light in the visible and ultraviolet range
what are two ways that absorption spectra can be represented?
- a color bar with peak areas of absorption represented by black lines
- a graph with the absolute absorption as a function of wavelength
what happens if one excites a fluorescent substance with ultraviolet radiation?
it will begin to glow with visible light
what are 3 examples of a fluorescent substance?
- ruby
- emerald
- the phosphors found in fluorescent lights
what happens after the electron is excited to a higher energy state by ultraviolet radiation? + char of what happens
the electron in the fluorescent substance returns to its original state in two or more steps
each step involves less energy, so at each step, a photon is emitted with a lower frequency (longer wavelength) than the absorbed ultraviolet photon
what are the criteria for the wavelength of the emitted photon to be seen as light of the particular color responding to that wavelength?
if the wavelength of the emitted photo is within the visible range of the electromagnetic spectrum
what causes the wide range of colors of fluorescent lights (whitish green office lighting to glaring neon)?
it is a result of the distinct multi-step emission spectra of different fluorescent materials
defn: mass defect
the difference between the actual mass of every nucleus and the assumed mass of the nucleus (as the sum of the masses of all the protons and neutrons within it)
