Difference between revisions of "Planck's Constant Determination"
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=Description of the Experiment= | =Description of the Experiment= | ||
| − | The purpose of this experiment is to study the photoelectric effect in metal and the determination of | + | The purpose of this experiment is to study the photoelectric effect in metal and the determination of Planck's constant, since the former is of a quantic nature. |
The light created by a mercury bulb is passed through a diffraction net to separate its spectral lines (i.e., the colours of the spectrum, just as a rainbow is a separation of the sunlight) and is used to force the emission of electrons in a photoelectric cell for each colour. | The light created by a mercury bulb is passed through a diffraction net to separate its spectral lines (i.e., the colours of the spectrum, just as a rainbow is a separation of the sunlight) and is used to force the emission of electrons in a photoelectric cell for each colour. | ||
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| + | <div class="toccolours mw-collapsible mw-collapsed" style="width:420px"> | ||
| + | '''Links''' | ||
| + | <div class="mw-collapsible-content"> | ||
| + | |||
| + | *Video: rtsp://elabmc.ist.utl.pt:554/g.sdp | ||
| + | *Laboratory: Básico em [http://e-lab.ist.eu e-lab.ist.eu] | ||
| + | *Control room: g | ||
| + | *Level: *** | ||
| + | |||
| + | </div> | ||
| + | </div> | ||
| + | |||
=Experimental Apparatus= | =Experimental Apparatus= | ||
| − | + | [[File:Espectro_dos_leds.png|thumb|alt=Led spectrum|Figure 1: Led spectrum.]] | |
| + | |||
| + | The photoelectric cell is a PASCO AP-9368, capacitor type cell, where one of the plates emits photoelectrons. These are stored in the other plate, which creates an electric potential between plates (and consequently, between the photocell's terminals). This potential increases with time until a maximum is reached. At this point, the capacitor stops charging (the potential energy is greater than the photoelectron's kinetic energy). For each wavelength, the electric potential will be different. | ||
| + | |||
| + | The photocell's terminals are grounded after measurements are taken to ensure that the capacitor is discharged when the next experiment starts. This allows an accurate determination of how long it takes for the capacitor to charge when considering different radiation intensities (not to be confused with the photoelectron's energy). | ||
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| + | Each color's (led) efficiency is different, so the intensity will also be different. This means that the charging time will be influenced by these factors. | ||
| + | |||
| + | {| border="1" style="text-align: center;" | ||
| + | |+ Table 1 – Spikes in the Led spectrum | ||
| + | |- | ||
| + | ! Color | ||
| + | !Frequency (Hz) | ||
| + | !Wave lenght (nm) | ||
| + | !Led spectrum | ||
| + | |- | ||
| + | |Blue.ab | ||
| + | |638.7 | ||
| + | |469.70 | ||
| + | |[[File:Espectro_Azul.ab.txt|Azul.ab]] | ||
| + | |- | ||
| + | |Blue | ||
| + | |684.6 | ||
| + | |438.20 | ||
| + | |[[File:Espectro_Azul.txt|Azul]] | ||
| + | |- | ||
| + | |Red | ||
| + | |482.2 | ||
| + | |622.21 | ||
| + | |[[File:Espectro_Vermelho.txt|Vermelho]] | ||
| + | |- | ||
| + | |Yellow | ||
| + | |514.4 | ||
| + | |583.16 | ||
| + | |[[File:Example.txt|Amarelo]] | ||
| + | |- | ||
| + | |Green | ||
| + | |530.8 | ||
| + | |565.22 | ||
| + | ||[[File:Espectro_Verde.txt|Verde]] | ||
| + | |} | ||
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=Links= | =Links= | ||
*[[Determinação da Constante de Planck | Portuguese version (Versão em Português)]] | *[[Determinação da Constante de Planck | Portuguese version (Versão em Português)]] | ||
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