WACE Physics — Unit 4
Photoelectric Effect — Flashcards & Quiz
The photoelectric effect is the emission of electrons from a metal when light shines on it, and WACE Physics Year 12 Unit 4 treats it as the key experimental evidence for the photon model of light. Einstein's equation hf = φ + KE_max ties photon energy to the maximum kinetic energy of ejected electrons, and the threshold frequency represents the minimum frequency for any emission.
Sample Flashcards
Q1: Describe the photoelectric effect and why wave theory fails.
Light ejects electrons from a metal. Wave theory predicts any frequency works with enough intensity. Observations: (1) threshold frequency f₀ required, (2) KE depends on frequency not intensity, (3) emission is instantaneous.
Q2: State Einstein's photoelectric equation.
E_k(max) = hf − φ, where h = 6.626 × 10⁻³⁴ J s, f is frequency, φ is the work function (minimum energy to remove an electron). At threshold: E_k = 0, so φ = hf₀.
Q3: How does a stopping voltage experiment work?
Reverse voltage V_stop stops all ejected electrons: eV_stop = E_k(max) = hf − φ. Plot V_stop vs f: slope = h/e, x-intercept = f₀.
Sample Quiz Questions
Q1: Increasing light intensity increases photoelectron kinetic energy.
Answer: FALSE
Intensity increases the NUMBER of electrons, not their energy. KE depends on frequency.
Q2: Below the threshold frequency, no electrons are emitted regardless of intensity.
Answer: TRUE
Each photon must have energy ≥ φ. Below f₀, individual photon energy is insufficient.
Q3: The photoelectric effect provides evidence for the particle nature of light.
Answer: TRUE
Requires photons to explain threshold frequency and instantaneous emission.
Last updated: March 2026 · 3 flashcards · 3 quiz questions