Smartphone-based measurement of the Planck’s constant with light-emitting diodes

Abstract

Presented in this article is an alternative and cost-effective method for measuring Planck's constant with light-emitting diodes (LEDs). Essential in the presentation is the apparent linear plot of the voltage against light intensity associated to each LED; such a plot reveals the threshold or minimum voltage that turns on the LED. Those threshold voltages associated to all LEDs used are theoretically related to the frequency of the emitted light and to the Planck's constant. Hence, in the experiment presented, the determination of the value of Planck's constant to be equal to 6.1(±1) × 10 −34 Js. This result is in error by 7.9% in comparison to the accepted value of 6.626 075 54 × 10 −34 Js but it appears to be good enough for educational use.

Determining Planck’s constant with LEDs—what could possibly go wrong?

“…Voltage versus light intensity measurements curves can be extrapolated to obtain the threshold voltage at which light is first emitted. This approach has been successful using mobile phones as the light detector [10].…”

“…Perhaps the first article to discuss the LED energy structure and a method of using that structure to determine Planck's constant appeared in 1974 [7,8]. Over many years, descriptions of this experiment have appeared in journal articles [9,10] and on the Web. A search for 'Planck constant LED' will provide links to many documents, many of which are lab write-ups created for students, and some YouTube videos.…”

Algorithm based determination of the Planck’s constant

“…There are numerous methods to determine the Planck's constant [2][3][4][5][6][7][8][9][10][11][12][13]. In the undergraduate laboratories the Planck's constant is experimentally calculated using light emitting diode (LEDs) of different colours.…”

To measure the wavelength of the light of a LED using LDR: a simple and an inexpensive method

“…A typical laboratory method is, to measure the intensity of the given LED light using light meter or luxmeter [2]. In some recent studies, the intensity of the LED light was measured using in built ambient light sensor in a smart phone [3]. The luxmeter or the light sensor in a smart phone, both are expensive.…”