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55 ideas · 69 connections
Charge flow and electrical power Kirchhoff’s second law tracks energy per charge Internal resistance separates e.m.f. from terminal voltage One photon supplies one electron’s energy Photoelectron energy determines its maximum speed Accelerating voltage becomes electron kinetic energy LED voltage links electrical and photon energy A Planck-constant experiment needs uncertainty analysis Charge and current4.1 Energy, power and resistance4.2 Measurements and uncertainty2.2.1 Kinetic and potential energies3.3.2 E.m.f. and potential difference4.2.2 Series and parallel circuits4.3.1 Internal resistance4.3.2 Photons4.5.1 The photoelectric effect4.5.2
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Physics connection

LED voltage links electrical and photon energy

OCR A AS Physics · Two ideas, one explanation

The energy transferred per electron by an LED’s threshold voltage can be compared with the energy of emitted photons. Different colours give a route to estimating Planck’s constant.

eV ≈ hf

Follow the reasoning

  1. Measure a consistent threshold voltage for each LED.
  2. Use the frequency of its emitted light.
  3. Plot voltage against frequency and relate the gradient to h/e.
Specification outcomes (4)
  • 4.2.2(d) Use energy transfer equations W = VQ and W = EQ.
  • 4.5.1(c) Use E = hf and E = hc / λ to calculate energy of a photon.
  • 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.
Open the official OCR AS specification ↗

H156 v2.0 · May 2026

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