Measurement of Planck`s constant

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Measurement of Planck’s constant

Francesco Gonnella Matteo 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-doped semiconductor P-doped semiconductor

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  V d

Depletion zone I = 0

V = 0

LED: Light Emitting Diode

I = 0

V = 0 I ≠ 0

V > 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 E gap ) • 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 = eV th where e = 1.602x10

-19 C and V th 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:

eV th = hf

To-do list

You must determine the threshold voltage of the LED, V th 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 V for I= 0 using a linear fit of the straight part of the data.

That value is a good estimation of V th 4) Evaluate h using the relation

eV th =hf

, knowing e and f (the latter is written in the LED datasheet)

Experimental setup

ocular Readout switch Power controller LED power I/0 Measurement connectors 12 V current voltage

Pay attention to the instruments Ammeter Voltmeter

Let’s get started!

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