Quantum Physics

What Quantum Physics covers

Where classical physics runs out: the photon model, the photoelectric effect and what it proves, and the wave nature of the electron.

The 5 subtopics

Each one has its own page.

• Photons, electronvolts and the Planck constant from LEDsRecall 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.Open →
• Demonstrating the photoelectric effectRecall 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.Open →
• Work function and Einstein's equationRecall 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.Open →
• Electron diffractionRecall questions on the experimental evidence for electron diffraction through a thin slice of polycrystalline graphite.Open →
• The de Broglie equationRecall questions on λ = h/p and on what it implies about matter.Open →

What you need to know

Answer each one before you reveal it.

Take Quantum Physics further

The same content, four other ways.

Commonly confused

Pairs that lose marks when they are blurred together.

• Photoelectric effect vs Electron diffraction

  Photoelectric effect: electron emission caused by incident electromagnetic radiation. Electron diffraction: wave-like spreading of electrons through a crystal.

• Excitation vs Ionisation

  Excitation: raising an electron to a higher bound energy level. Ionisation: removing an electron completely from an atom.

• Emission spectrum vs Absorption spectrum

  Emission spectrum: wavelengths emitted during downward energy transitions. Absorption spectrum: wavelengths removed during upward energy transitions.

Questions from this topic

Each one with the model answer underneath.

1. 1

   What does the photon model describe about the nature of electromagnetic radiation?

   Model answer

   Electromagnetic radiation has a particulate nature, consisting of discrete packets of energy called photons.

2. 2

   Define a photon.

   Model answer

   A photon is a quantum of energy of electromagnetic radiation, representing the smallest indivisible unit of light energy.

3. 3

   Calculate the photon energy when Planck constant = 6.63 × 10⁻³⁴ J s, frequency = 6.22 × 10¹⁴ Hz.

   Model answer

   Photon energy = 6.63 × 10⁻³⁴ × 6.22 × 10¹⁴ = 4.12 × 10⁻¹⁹ J.

4. 4

   State the alternative equation for photon energy in terms of wavelength.

   Model answer

   E = hc/λ, where h is the Planck constant, c is the speed of light, and λ is the wavelength.

5. 5

   Calculate the photon energy when Planck constant = 6.63 × 10⁻³⁴ J s, speed of light = 3.00 × 10⁸ m s⁻¹, wavelength = 4.50 × 10⁻⁷ m.

   Model answer

   Photon energy = (6.63 × 10⁻³⁴ × 3.00 × 10⁸) ÷ (4.50 × 10⁻⁷) = 4.42 × 10⁻¹⁹ J.

6. 6

   Define the electronvolt.

   Model answer

   The electronvolt is a unit of energy equal to the energy gained by an electron when accelerated through a potential difference of one volt.

What is inside Levo

Six ways to work the same material.

Quantum Physics revision questions

What does Quantum Physics cover in OCR A-Level Physics A?

5 subtopics: 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. Each one has its own page with questions and model answers.

How is Quantum Physics organised?

By the OCR H556 specification, subtopic by subtopic, so it matches the order you are taught it in.