Photons and the photoelectric effect
Введено| English | Значение |
|---|---|
| photon/ˈfəʊtɒn/ | фотон |
| work function/wɜːk ˈfʌŋkʃn/ | работа выхода |
What would explain this observation?
- Bright low-frequency light can fail to eject electrons while dim higher-frequency light succeeds. Photon 光子 energy depends on frequency, not intensity alone.
Build the model
- A photon has energy proportional to frequency.
- The work function 逸出功 is the minimum energy needed to release an electron from a surface.
- Above threshold, excess photon energy can become electron kinetic energy.
- photon: A quantum of electromagnetic radiation.
- work function: Minimum surface energy needed to release an electron.
At fixed above-threshold frequency, increasing intensity mainly increases what?
Сложность 1/5 · 100 монет + небольшой бонус за первое выполнение сегодня
Photon energy depends only on frequency (E = hf), so raising intensity at fixed frequency adds more photons, each unchanged. More photons above threshold liberate more electrons per second; the work function is a property of the surface.
Match each technical term to its precise meaning.
Сложность 2/5 · 140 монет + небольшой бонус за первое выполнение сегодня
Use the definitions to distinguish related quantities and processes.
Choose evidence that can test it
- Use photon energy = Planck constant × frequency.
- Maximum kinetic energy = photon energy - work function.
- Increasing intensity at fixed frequency increases photon arrival rate, not individual photon energy.
In the lab: Read axes carefully on a stopping-potential or kinetic-energy graph. Identify threshold frequency from the zero-energy intercept. State the metal and experimental conditions because work function is material-specific.
Which two habits make the investigation or model in this case more defensible?
Сложность 2/5 · 140 монет + небольшой бонус за первое выполнение сегодня
Stating the conditions and assumptions lets others repeat the work exactly, and recording the supporting evidence lets them check the conclusion. Hiding disagreeing results removes the evidence that could challenge a wrong conclusion, and one measurement can never establish a wider claim.
Work from known quantities
- Known: photon energy is 5.0 electronvolts and work function is 2.0 electronvolts.
- Maximum kinetic energy = photon energy - work function = 5.0 - 2.0 = 3.0 electronvolts.
- A 1.5 electronvolt photon cannot cause emission from that surface in this model.
Your turn: Photon energy is 4.8 eV and work function 2.1 eV. Find maximum kinetic energy.
Photon energy is 4.8 eV and work function 2.1 eV. Find maximum kinetic energy.
Сложность 2/5 · 140 монет + небольшой бонус за первое выполнение сегодня
The result is 2.7 eV. Known: photon energy 4.8 eV; work function 2.1 eV. Use maximum kinetic energy = photon energy - work function. KE max = 4.8 - 2.1 = 2.7 eV. A photon below 2.1 eV would eject nothing, however intense the light.
Check the conclusion and its limits
- Electrons do not accumulate many sub-threshold photons in the elementary single-photon model.
- Do not confuse photon number with photon energy.
Not true: Doubling light intensity doubles each photon energy at fixed frequency. Intensity is the number of photons arriving per second; photon energy is set by frequency alone (E = hf). Doubling intensity doubles the electron count, not each electron's energy - exactly what the photoelectric equation shows.
- A photon has energy proportional to frequency.
- Use photon energy = Planck constant × frequency.
- Watch for: electrons do not accumulate many sub-threshold photons in the elementary single-photon model.
Write from a maximum kinetic energy of 4.0 electronvolts
- Photon energy is 6.4 electronvolts and the work function is 2.4 electronvolts.
- Find the maximum kinetic energy. A 2.0 electronvolt photon causes no emission. Intensity does not set photon energy.
Doubling light intensity doubles each photon energy at fixed frequency.
Сложность 1/5 · 100 монет + небольшой бонус за первое выполнение сегодня
Intensity is the number of photons arriving per second; photon energy is set by frequency alone (E = hf). Doubling intensity doubles the electron count, not each electron's energy - exactly what the photoelectric equation shows.
A quantum of electromagnetic radiation: write the technical term.
Сложность 1/5 · 100 монет + небольшой бонус за первое выполнение сегодня
photon means A quantum of electromagnetic radiation.
Photon energy is 6.4 electronvolts and the work function is 2.4 electronvolts. What is the maximum kinetic energy, and why does doubling the intensity not double the photon energy?
Maximum kinetic energy is photon energy minus the work function. Photon energy depends on frequency, not on intensity.
What is the maximum kinetic energy?
Сложность 1/5 · 100 монет + небольшой бонус за первое выполнение сегодня
6.4 minus 2.4 is 4.0 electronvolts. The prompt uses 4.8 and 2.1. Other options — 6.4 electronvolts (the photon energy); 2.7 electronvolts (the figure given in the question).