Description
Solar cells and LEDs can be used to demonstrate quantum phenomena by their apparent bandgap in both the detection and production of light. The bandgap and the wavelength of emitted light can be used to calculate Planck’s constant. As part of Quantum Enrichment days (sponsored by an IYQ grant$^1$ from the AIP) a circuit was developed to allow both the measurement of Planck’s constant and qualitative comparison of bandgaps and the spectra of LEDs of different colour. This circuit was used in the first Quantum Enrichment day at Kingscote school$^1$ and has now been added into a practical in the “Physics Skills Enhancement Microcredential”.$^2$
In three subsequent Quantum Enrichment days at Flinders University, we used a commercial instrument that allowed similar measurements of Planck’s constant but with more convenience and a greater wavelength range. A more accurate value of the constant was obtained by combining the readings for all the LEDs to eliminate some physical complications.
While the circuit marked on the commercial instrument shows clearly what is happening inside, it is likely to be a “black box” with mysterious hidden workings to students who are not familiar with electrical circuits. We therefore rotated students to a separate session with hands-on breadboarding of circuits with a minimum of components (with just a solar panel and LEDs). They could emulate the operation of the commercial instrument by direct measurement of the voltage across the LEDs. In addition, working with individual components enabled other observations to be made that reinforced the basic concept. These also facilitated making the subject more interesting for students by setting questions and challenges that required understanding to answer and implement them.
This activity provides a tangible demonstration of abstract quantum concepts that could be used for both outreach and introductory university physics topics.
$^1$https://www.aip.org.au/SA-Branch/13558963
$^2$https://flinders.badges.parchment.au/public/badges/kQZHZ86tRrWBIucNrZCcAA
| I am the presenting author | Yes |
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