CCEA A Level Physics
CCEA A Level Physics 2.5 Quantum Physics and 2.6 Wave-Particle Duality Exam Questions
Free CCEA A Level Physics revision for 2.5 Quantum Physics and 2.6 Wave-Particle Duality: what you need to know, common mistakes and exam-style questions with answers. Covers photons, the photoelectric effect, energy levels, lasers, X-rays, CT scanning, electron diffraction and the de Broglie equation.
Practise 2.5 Quantum Physics and 2.6 Wave-Particle Duality with past papers
Once you have learnt this topic, find the 2.5 Quantum Physics and 2.6 Wave-Particle Duality questions in real CCEA A Level Physics past papers and mark them with the mark scheme. Doing lots of real questions is the quickest way to learn how examiners ask about each idea.
StemUp mark scheme flashcards
A-Level Physics Flashcards for 2027 Onwards
Every answer is written in mark scheme wording, so you learn exactly what examiners give marks for. Then test yourself with the questions on this page.
From £10.99View flashcards
About CCEA A Level Physics 2.5 Quantum Physics and 2.6 Wave-Particle Duality
These sections in Unit AS 2: Waves, Photons and Astronomy show that light can behave as particles and electrons as waves. You need the photon energy equation, the photoelectric effect with work function and threshold frequency, and energy levels in atoms explaining line spectra. The applications are lasers, the production of X-rays and CT scanning. Wave-particle duality then compares wave and photon models of light, uses electron diffraction as evidence that matter has wave properties and applies the de Broglie equation. Examiners often ask why the wave model fails for the photoelectric effect, energy level transitions in electronvolts and de Broglie wavelength calculations.
What you need to know
- Photons Light is emitted and absorbed in packets called photons with energy E = hf = hc/λ. 1 eV = 1.6 x 10^-19 J, the energy gained by an electron accelerated through 1 V.
- Photoelectric effect Electrons are emitted from a metal surface only if the light frequency is above the threshold frequency f0. hf = φ + KE(max), where the work function φ = hf0. Increasing intensity increases the number of electrons emitted, not their maximum kinetic energy.
- Energy levels and spectra Electrons in atoms occupy discrete energy levels. A transition between levels emits or absorbs a photon of energy hf = E1 - E2, giving line emission or absorption spectra.
- Lasers Rely on stimulated emission: an incoming photon causes an excited atom to emit an identical photon in phase. A population inversion, usually involving a metastable state, is needed so stimulated emission outweighs absorption.
- X-rays and CT scanning X-rays are produced when high-energy electrons strike a metal target, giving a continuous spectrum plus characteristic lines. In CT scanning an X-ray source and detectors rotate around the patient, and a computer builds cross-sectional slices into a 3D image.
- Wave-particle duality Interference and diffraction need the wave model; the photoelectric effect needs the photon model. Electron diffraction through graphite shows particles have wave properties, with de Broglie wavelength λ = h/p = h/mv.
Common mistakes in 2.5 Quantum Physics and 2.6 Wave-Particle Duality
- Saying brighter light gives photoelectrons more energy; maximum kinetic energy depends only on frequency.
- Forgetting to convert between electronvolts and joules before using E = hf.
- Describing a laser without mentioning population inversion and stimulated emission.
- Using the speed of light in the de Broglie equation for an electron; use the electron's own momentum mv.
- Saying the work function is the energy of the emitted electron; it is the minimum energy needed to remove an electron from the surface.
Try three 2.5 Quantum Physics and 2.6 Wave-Particle Duality exam-style questions
1. Light of wavelength 450 nm falls on a metal with work function 2.3 eV. Calculate the photon energy in eV and the maximum kinetic energy of the photoelectrons. (4 marks)
Show the mark scheme answer
E = hc/λ = 6.63 x 10^-34 x 3.0 x 10^8 / 450 x 10^-9 = 4.42 x 10^-19 J; = 4.42 x 10^-19 / 1.6 x 10^-19 = 2.76 eV; KE(max) = 2.76 - 2.3 = 0.46 eV; = 7.4 x 10^-20 J.
2. Calculate the de Broglie wavelength of an electron moving at 2.0 x 10^6 m s-1. (2 marks)
Show the mark scheme answer
p = 9.11 x 10^-31 x 2.0 x 10^6 = 1.82 x 10^-24 kg m s-1; λ = h/p = 6.63 x 10^-34 / 1.82 x 10^-24 = 3.6 x 10^-10 m.
3. Explain why the wave model of light cannot explain the existence of a threshold frequency. (3 marks)
Show the mark scheme answer
In the wave model energy is spread continuously and depends on intensity; so any frequency should eventually release electrons if the light is intense or shone for long enough; in fact no electrons are emitted below f0 however intense the light, because each electron absorbs one photon of energy hf.
2.5 Quantum Physics and 2.6 Wave-Particle Duality FAQs
What does CCEA A Level Physics 2.5 and 2.6 cover?
Photon energy, the photoelectric effect, energy levels and spectra, lasers, X-ray production and CT scanning, wave and photon models of light, electron diffraction and the de Broglie equation.
Which unit are quantum physics and wave-particle duality examined in?
Both are in Unit AS 2: Waves, Photons and Astronomy.
What equations do I need for 2.5 and 2.6?
E = hf = hc/λ, hf = φ + KE(max), φ = hf0, hf = E1 - E2 and λ = h/p = h/mv, along with the conversion 1 eV = 1.6 x 10^-19 J.
