VCE Physics — Unit 4 AOS 1
Photoelectric Effect — Flashcards & Quiz
The photoelectric effect is the ejection of electrons from a metal surface when light shines on it, and VCE Physics Unit 4 AOS 1 treats it as the key experimental evidence for the photon model. Einstein's equation hf = φ + KE_max ties photon energy to the maximum kinetic energy of ejected electrons, and the threshold frequency shows that wave intensity alone cannot explain the phenomenon.
Sample Flashcards
Q1: Describe the photoelectric effect and what it demonstrates.
When light above a threshold frequency hits a metal surface, electrons are emitted instantly. Below the threshold, no electrons are emitted regardless of intensity. Kinetic energy of emitted electrons: KE_max = hf − φ, where φ is the work function. This proves light has particle properties (photons).
Q2: What is the work function and how does it relate to threshold frequency?
The work function (φ) is the minimum energy needed to remove an electron from the metal surface, measured in joules or electronvolts. Threshold frequency: f₀ = φ/h. Below f₀, photon energy is insufficient to liberate electrons.
Q3: How does the kinetic energy of photoelectrons depend on light frequency and intensity?
KE_max = hf − φ. Kinetic energy increases linearly with frequency (slope = h). Increasing intensity increases the NUMBER of photoelectrons emitted (more photons) but does NOT change KE_max. Each photon interacts with one electron.
Q4: Why does classical wave theory fail to explain the photoelectric effect?
Classical wave theory predicts: 1) Any frequency should work given enough time for energy to accumulate. 2) Brighter light should give higher KE electrons. 3) Emission should be delayed. Experiment shows: 1) Threshold frequency exists. 2) Intensity affects current, not KE. 3) Emission is instantaneous. Photon theory explains all observations.
Sample Quiz Questions
Q1: In the photoelectric effect, increasing light intensity increases the kinetic energy of emitted electrons.
Answer: FALSE
Intensity affects the NUMBER of photoelectrons (current) but not their maximum kinetic energy. Only frequency affects KE_max.
Q2: Below the threshold frequency, no photoelectrons are emitted regardless of light intensity.
Answer: TRUE
Below f₀, photon energy hf < work function φ, so no electrons are liberated. Intensity does not compensate for insufficient photon energy.
Q3: The work function is the minimum energy required to remove an electron from a metal surface.
Answer: TRUE
φ is the binding energy of the least-bound electron. Photon energy must exceed φ for emission to occur.
Related Concepts
Last updated: March 2026 · 4 flashcards · 4 quiz questions