Quantum Physics | OCR A-Level Physics A (H556)
Quantum Physics
- 60 questions
- 5 subtopics
- Module 4: Electrons, waves and photons
- Paper 2 and Paper 3
Where classical physics runs out: the photon model, the photoelectric effect and what it proves, and the wave nature of the electron..
It covers photons, electronvolts and the Planck constant from LEDs, demonstrating the photoelectric effect, work function and Einstein's equation, electron diffraction and the de Broglie equation.
Sample questions from Quantum Physics
Answer each one closed book first, then open the answer.
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Photons, electronvolts and the Planck constant from LEDs
Define the electronvolt.
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The electronvolt is a unit of energy equal to the energy gained by an electron when accelerated through a potential difference of one volt. -
Photons, electronvolts and the Planck constant from LEDs
Calculate the Planck constant when elementary charge = 1.60 × 10⁻¹⁹ C, threshold voltage = 1.9 V, wavelength = 6.40 × 10⁻⁷ m, speed of light = 3.00 × 10⁸ m s⁻¹.
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Planck constant = (1.60 × 10⁻¹⁹ × 1.9 × 6.40 × 10⁻⁷) ÷ (3.00 × 10⁸) = 6.49 × 10⁻³⁴ J s. -
Demonstrating the photoelectric effect
Before shining light on the zinc plate in a photoelectric effect demonstration, how must the electroscope be charged and what is observed?
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The electroscope must be charged negatively, causing the gold leaf to deflect. -
Demonstrating the photoelectric effect
Describe the nature of the interaction between photons and electrons in the photoelectric effect.
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There is a one-to-one interaction between a single photon and a single surface electron. -
Work function and Einstein's equation
Calculate the threshold frequency when work function = 6.9 × 10⁻¹⁹ J, Planck constant = 6.63 × 10⁻³⁴ J s.
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Threshold frequency = 6.9 × 10⁻¹⁹ ÷ (6.63 × 10⁻³⁴) = 1.04 × 10¹⁵ Hz. -
Work function and Einstein's equation
Above the threshold frequency, how does the rate of emission of photoelectrons depend on the intensity of incident radiation?
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The rate of emission of photoelectrons is directly proportional to the intensity of the incident radiation. -
Electron diffraction
Describe the pattern observed on the fluorescent screen when electrons are diffracted by graphite.
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Concentric circular rings appear on the fluorescent screen. -
Electron diffraction
Explain why electrons produce a diffraction pattern when passing through graphite.
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The electrons are diffracted by the regular arrangement of carbon atoms, and the spacing between atomic layers acts as a diffraction grating.
The 5 subtopics
One subtopic is one session. Work down the list.
| Subtopic | What it covers | Questions |
|---|---|---|
| Photons, electronvolts and the Planck constant from LEDs | Recall questions on the photon model, photon energy in terms of frequency and wavelength, the electronvolt, and estimating the Planck constant from the threshold voltages of LEDs. | 17 |
| Demonstrating the photoelectric effect | Recall questions on what the photoelectric effect is, the gold-leaf electroscope and zinc plate demonstration, the one-to-one photon-electron interaction, and why wave theory cannot explain a threshold frequency. | 8 |
| Work function and Einstein's equation | Recall questions on the work function and threshold frequency, Einstein's photoelectric equation and calculations, and how intensity affects the rate of emission but not the maximum kinetic energy of photoelectrons. | 17 |
| Electron diffraction | Recall questions on the experimental evidence for electron diffraction through a thin slice of polycrystalline graphite. | 9 |
| The de Broglie equation | Recall questions on λ = h/p and on what it implies about matter. | 9 |
How the guide is worked
Answering a question from memory stores it far better than reading the answer again. The guide runs that as a fixed procedure on one subtopic at a time, about twenty minutes a session.
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Step 1 · Closed book
Cover the answers. Work through one subtopic and write down what you can. Leave blanks where you have nothing.
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Step 2 · Open book
Go back to the top. Read each printed answer and write it out in full, including the ones you had right.
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Step 3 · Closed book again
Same questions, same order, from memory. The gap between pass one and pass three is the session result.
Read the full method, the return schedule and the research behind it.
Nearby topics
OCR A-Level Physics A Active Recall Guide
Every topic, not just this one. 1,862 questions with their answers.