Photons
Explore photons within quantum physics. Some interactions transfer energy in discrete amounts. Photon energy links frequency to the photoelectric effect, while diffraction reveals the wave behaviour of particles.
Specification outcomes (6)
- 4.5.1(a) Describe the particulate (photon) nature of electromagnetic radiation.
- 4.5.1(b) Define a photon as a quantum of energy of electromagnetic radiation.
- 4.5.1(c) Use E = hf and E = hc / λ to calculate energy of a photon.
- 4.5.1(d) Define the electronvolt (eV) as a unit of energy.
- 4.5.1(e)(i) Use LEDs and eV = hc / λ to estimate the value of Planck’s constant.
- 4.5.1(e)(ii) Determine Planck’s constant using different coloured LEDs experimentally.
H156 v2.0 · May 2026
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An optical sensor alternates between a green source of wavelength 520 nm and a red source of wavelength 650 nm. Treat each source as monochromatic and use its wavelength in a vacuum. Each source emits 2.0 μJ of light energy in a burst. Use c = 3.00 × 10⁸ m s⁻¹ and h = 6.63 × 10⁻³⁴ J s. (a) Calculate the frequency of the green light. [2] (b) Calculate the energy of one green photon and one red photon. [3] (c) Calculate the number of photons emitted in one green burst. [2] (d) A technician claims that equal-energy bursts contain equal numbers of photons. Calculate the ratio (red photon count)/(green photon count) and explain whether the claim is correct. [3]
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