AQA AS Level Physics Paper 2, June 2024: Question 14

1 mark · Easy difficulty · Multiple Choice

Identify which property of radiation from light source P must be greater than from light source Q to cause photoelectron emission from a metal surface.

Practise this question

Question

Multiple choice question 14. Monochromatic radiation from light source P incident on a metal surface emits photoelectrons, whereas light source Q does not. Four options are given: A, frequency; B, intensity; C, speed; D, wavelength.
Question text

14 Monochromatic radiation from light source P is incident on a metal surface and

photoelectrons are emitted.

When monochromatic radiation from light source Q is used, no photoelectrons are emitted.

Which property of the radiation from P must be greater than that from Q?

[1 mark]

A frequency

B intensity

C speed

D wavelength

Mark scheme

Show the mark scheme Mark scheme for question 14 indicating that the correct answer is A, frequency.

14 A frequency

How to answer it

Threshold Frequency in the Photoelectric Effect

📌 What this question tests

This question assesses your fundamental understanding of the photoelectric effect, specifically the threshold frequency concept. It tests whether you can distinguish between wave-particle interaction properties (frequency determining photon energy vs. intensity determining photon flux) and link them directly to whether photoelectrons can be emitted from a metal surface.

Question 1.4 Breakdown

Evaluating Monochromatic Radiation and Electron Emission

✅ Correct Answer

A — frequency

Mark allocation: [1 mark] awarded for selecting option A.

💡 Key Knowledge

  • Energy of a single incident photon is given by E = hf .
  • Photoemission only occurs if the photon energy is greater than or equal to the work function ( phi ) of the metal.
  • Therefore, the frequency f must be greater than or equal to the threshold frequency ( f₀ ).

🧠 Exam Technique

Read the stem carefully: Source P causes emission, while Source Q does not. This means the photons from P have energy above the work function, whereas photons from Q are below it. Since E = hf , a higher energy implies a higher frequency.

❌ Common Errors

Many students confuse intensity (Option B) with photon energy. Increasing intensity increases the number of photons per second, but not the energy of individual photons. If a single photon from source Q lacks enough energy to liberate an electron, piling more low-energy photons onto the metal (increasing intensity) still results in zero photoemission.

Topics

Physics · 3.2 Particles and radiation

Question and mark scheme from the AQA AS Level Physics examination, Paper 2, June 2024. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.