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!