Measuring Planck's constant with LEDs
Resource: https://www.scienceinschool.org/2014/issue28/planck
What is a diode and how can it be used to measure Planck's constant:
Electric circuit for measuring
the voltage-current response
of each LED. From left to
right: battery, potentiometer
or rheostat, voltmeter,
ammeter, LED.
Students might only use a voltmeter initially and determine the cut-off voltage by observation. Their value for Planck’s will be pretty broad. This then offers a good opportunity to refine and develop as a PI using measures of current and voltage.
Linear regression gives the following value for the gradient (m):
m = 1.24811 x 10-6 Vm (volt metres) From this, the Planck constant can finally be calculated. From above, m = hc/e, so:
h = em/c (4)
= 1.6022 x 10-19 x 1.24811 x 10-6 /
2.9979 x 108
= 6.6704 x 10-34 Js (joule seconds)