![]() That makes the relative response of both techniques somewhat different, function of the wavelength of the light, the energy of photons.Īs we make the measurments in specific bandwidth (filters), that are not very large, the differences between both are usually neglected. By the way such sensors are not sensitive to the energy of the photons, they are only photon-counting devices. The accumulation of electrons charges into that capacitor results in a voltage that is then amplified and converted to digital ADUs. In photovoltaic sensors the liberated electron moves at relatively low spead into the sillicon cristal and then is trapped into a potential well (or a physical capacitor in CMOS). By the way the PMT can be used as both a light intensity measuring device and/or a photon-counting device. The current INTENSITY of the pulse is function of the energy of the photon. The result is one current pulse on the anode for each detected photon (the process is very fast). In PMT one photon liberates one electron to the vaccum (with a given probability), that electron is then multiplied by secondary emission in an avalanche from dynode to dynode depending its energy. There are some physics difference between both. The photoelectic devices are vaccum tubes and more specifically the PMT (photo-multiplier-tubes), photovoltaic devices are the solid-state sensors like CCD, CMOS or even single PIN diodes. We are often using the "photoelectric" wording for both and this is somewhat confusing. I think André is considering the two modes that are specific to photoelectric devices and photovoltaic devices. In general, for stars, you cannot deduce the distance from just looking at the magnitude or even the light curve. ![]() But this only works for these special variables where you have this relationship between measurable quantities and the absolute brightness. There are variables of certain, special types where you can approximately tell their distance from analysing their lightcurves (plots of brightness over time), because their brighness variations will tell you something about their absolute brighness (how bright they look from a given distance), and you can measure their apparent brightness (how bright they appear to us on Earth) with your photometer, and from that you can figure out the distance. by putting filters in front of your sensor that will only let pass light of a given wavelength band) and you can then approximate the temperature from a formula based on the measurements in the two wavelengths.ĭistance is different thing altogether, and is generally one of the most difficult things to measure in astronomy. What you need to do is to measure the brighness at two different wavelengths (say blue and green, e.g. Do you have a specific device in mind?Īnyway.once you have a device that can measure brighness of a star, you can make estimates of its temperature IF the star is reasonably well behaved, that is if it's spectrum doesn't have odd emission or absorption features. I think it would be usefull to explain a bit more in detail what kind of device/hardware you are thinking of. ![]() Also the efficiency of converting photons to a photoelectric current will vary for different detector designs, materials etc. The calibration is necessary because if your detector has a larger collecting area for photons (larger aperture in optics), it will receive more photons per second compared to the same detector with a smaller aperture. To go from there to magnitudes, you need to calibrate the detector and then take the logarithm of the count rate to translate to the magnitude scale (because on this magnitude scale, an increase of magnitude of 1 means that the star is fainter by a factor of the 5th root of 100 (in terms of photons per second your detector will receive from that star, everything else unchanged). It took some time for physicists to come up with an explanation of this, until Albert Einstein found it in quantum physics at the beginning of the 20th century,Īnyway, this would allow you to measure a value that is proportional to the rate of photons per second hitting your detector. Voltage in the classical photoelectric experiment is related to the color of the incident light, it s current that is related to brightness. I'm not quite sure about the context of this question (which voltage are we talking about), but if this in any way related to a device using the photoelectric effect, then there really is no dependency of voltage to brightness!
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