measurement of planck’s constant francesco gonnella matteo mascolo
TRANSCRIPT
Measurement of Measurement of Planck’s constantPlanck’s constant
Francesco GonnellaFrancesco Gonnella
Matteo MascoloMatteo Mascolo
Our experiment• The goal of our experiment is to give an estimation of Planck’s constant;
• With our experimental setup, we expect to achieve an accuracy of 10-20%
The diode (1/2)“In electronics, a diode is a two-terminal electronic component with an asymmetric transfer characteristic, with low resistance to current flow in one direction, and high resistance in the other.”
(Wikipedia)
Silicon lattice N-dopedsemiconductor
P-dopedsemiconductor
The diode (2/2)A “hole” behaves exactly like an electron of positive electric charge:
• Negative charges are available in the n zone• Positive charges are available in the p zone
Depletion zone
Vd
V = 0
I = 0
LED: Light Emitting Diode
V = 0
I = 0
V > 0
I ≠ 0
Measuring h with a LED
• If one applies enough voltage to the junction, the LED starts emitting photons having all the same frequency, f (depending only on Egap)
• When the LED starts to glow, the energy E lost by every electron/hole jumping over the junction is converted to the energy of one single photon
• The energy of the charges in these conditions is E = eVth where e = 1.602x10-19 C and Vth is the LED threshold voltage.
• The energy of the emitted photon will be, according to Planck’s theory,is E = hf (with h Planck’s constant)
…energy is conserved in the process, so: eVeVthth = hf = hf
To-do list
You must determine the threshold voltage of the LED, Vth
1) You have to change the voltage applied to the LED, writing the corresponding current flowing through the junction
1) Draw the plot “I vs V” as shown in figure
1) Extrapolate the value of Vfor I= 0 using a linear fit ofthe straight part of the data.That value is a goodestimation of Vth
4) Evaluate h using the relation eVth=hf, knowing e and f(the latter is written in the LED datasheet)
Experimental setup
ocularLED power I/0
Power controller
Readoutswitch
12 V current voltage
Measurementconnectors
Pay attention to the instruments
Ammeter Voltmeter
Let’s get started!