leziosaure

Temperatura della luce, luce non visibile

Ho letto questo: In 1800, William Herschel discovered infrared radiation by passing sunlight through a prism and measuring the temperature just beyond the visible red spectrum. This discovery revealed that there are types of light invisible to the human eye.

Io parlo italiano.

Puoi darmi dettagli sul metodo usato da Herschel per misurare la temperatura di cui si parla?

Certo, sarò felice di fornirti dettagli sul metodo utilizzato da William Herschel per scoprire la radiazione infrarossa.

Nel 1800, Herschel stava conducendo esperimenti sulla natura della luce e del calore. Utilizzò un prisma per scomporre la luce solare nei suoi colori componenti, creando uno spettro visibile. Poi, posizionò una serie di termometri (strumenti per misurare la temperatura) lungo lo spettro, sia all'interno che all'esterno della parte visibile.

Il suo obiettivo iniziale era quello di determinare quale colore della luce visibile producesse il maggior calore. Tuttavia, notò che il termometro posizionato dopo la parte rossa dello spettro (la parte più a destra dello spettro visibile, dove la luce rossa è più intensa) registrava una temperatura più alta rispetto a quelli posizionati all'interno della parte visibile dello spettro.

Questo risultato inaspettato suggeriva che c'era una forma di radiazione che non era visibile all'occhio umano, ma che comunque trasportava energia termica. Herschel aveva scoperto la radiazione infrarossa, una forma di radiazione elettromagnetica con lunghezze d'onda più lunghe di quelle della luce visibile.

Il metodo di Herschel consisteva essenzialmente nei seguenti passaggi:

  1. Scomposizione della luce solare: utilizzò un prisma per scomporre la luce solare nei suoi colori componenti.
  2. Posizionamento dei termometri: posizionò una serie di termometri lungo lo spettro, sia all'interno che all'esterno della parte visibile.
  3. Misurazione della temperatura: misurò la temperatura registrata da ciascun termometro.
  4. Osservazione dei risultati: notò che il termometro posizionato dopo la parte rossa dello spettro registrava una temperatura più alta rispetto a quelli posizionati all'interno della parte visibile.

Questo esperimento semplice ma ingegnoso aprì la strada alla scoperta di altre forme di radiazione elettromagnetica e rivoluzionò la nostra comprensione della luce e dell'universo.

Una valutazione sulla difficoltà nel replicare l'esperimento in una scuola media italiana, con materiale, non dico di fortuna, ma insomma...

Replicare l'esperimento di Herschel in una scuola media italiana può essere un'esperienza didattica interessante e stimolante per gli studenti. Tuttavia, ci sono alcune sfide da considerare in termini di materiali e condizioni necessarie. Ecco una valutazione della difficoltà di replicare l'esperimento:

Materiali necessari:

Difficoltà:

Soluzioni possibili:

In generale, replicare l'esperimento di Herschel in una scuola media italiana potrebbe richiedere alcune modifiche e adattamenti per superare le difficoltà legate ai materiali e alle condizioni necessarie. Tuttavia, con un po' di creatività e ingegno, potrebbe essere possibile creare un esperimento didattico interessante e stimolante per gli studenti.

herschel-1997-xiv-experiments-on-the-refrangibility-of-the-invisible-rays-of-the-sun_1

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Phitos Trans.MDCCC.PatXpz B H G Downloaded from https://royalsocietypublishing.org/on 07 December 2024

[284] XIV.Experiments on the Refrangibility of the invisible Rays of the Sun. By William Herschel,LL.D. F.R.S. Read April 24,1800. IN that section of my former paper which treats of radiant heat,it was hinted,though from imperfect experiments, that the rangeof its refrangibility is probably more extensive than that of theprismatic colours; but, having lately had some favourable sun-shine, and obtained a sufficient confirmation of the same,it willbe proper to add the following experiments to those which havebeen given. I provided a small stand,with four short egs,and covered itwith white paper.* On this I drew five lines, parallel to one endof the stand, at half an inch distance from each other, but sothat the first of the lines might only be 44 of an inch from theedge. These lines I intersected at right angles with three others;the 2d and 3d whereof were, respectively, at 212 and at 4inchesfrom the first. The same thermometers that have before been markedNo. 1, 2, and 3, mounted upon their small inclined planes,werethen placed so as to have the centres of the shadow of theirballs thrown on the intersection of these lines. Now,settingmy little stand upon a table, I caused the prismatic spectrum tofall with its extreme colour upon the edge of the paper, so thatnone might advance beyond the first line. In this arrangement, ·See Plate XI. Downloaded from https://royalsocietypublishing.org/on 07 December 2024

Dr. HERSCHEL's Experiments, &c. 285 all the spectrum,except the vanishing last quarter of an inch,which served as a direction, passed down by the edge of thestand, and could not interfere with the experiments. I had alsonow used the precaution of darkening the window in which theprism was placed, by fixing up a thick dark green curtain,tokeep out as much light as convenient. The thermometers being perfectly settled at the temperatureof the room, I placed the stand so that part of the red colour,refracted by the prism, fell on the edge of the paper,before thethermometer No.1, and about half way, or 11 inch, towardsthe second: it consequently did not come before that, or the3d thermometer,both which were to be my standards. Duringthe experiment, I kept the last termination of visible redcarefully to the first line, as a limit assigned to it, by gentlymoving the stand when required; and found the thermometers,which were all placed on the second line, affected as follows. No.1. No.2. No.3. 45 45 44

49 45 44 51 443 44

一 501/4 4334 431/2 Here the thermometer No.1 rose 61 degrees, in 10 minutes,when its c ntre was placed 12 inch beyond visible light. In order to have a confirmation of this fact,I cooled thethermometer No. 1, and placed No.2 in the room of it: I alsoput No.3 in the place of No.2, and No.1 in that of No.3;and,having exposed them as before, arranged on the secondline,I had the following result. Downloaded from https://royalsocietypublishing.org/on 07 December 2024

286 Dr.HERSCHEL's Experiments on the Refrangibility No.2. No.3. No.1. 44 44 45 47 44 45 463/4 44 45 463/4 44 45 Here the thermometer No.2 rose 23/4 degrees, in 12 minutes;and being, as has been noticed before,much more sensible thanNo.1,it came to the temperature of its situation in a short time;but I left it exposed longer, on purpose to be perfectly assuredof the result. Its shewing but 23/4 degrees advance, when No.1shewed 612, has also been accounted for before. It being now evident that there was a refraction of rays comingfrom the sun, which, though not fit for vision,were yet highlyinvested with a power of occasioning heat, I proceeded to ex-amine its extent as follows. The thermometers were arranged on the third line,insteadof the second; and the stand was, as before, immersed up tothefirst,in the coloured margin of the vanishing red rays. Theresult was thus. No.1. No.2. No.3. 46 46 453/4 50 4612 46

513/4 463/4 464/4

524/4 47 463/4 Here the thermometer No.1 rose 51/4 degrees, in 13 minutes,at 1 inch behind the visible light of the red rays. I placed now the thermometers on the 4th line,instead ofthe 3d; and, proceeding as before,I had the following result. Downloaded from https://royalsocietypublishing.org/on 07 December 2024

of the invisible Rays of the Sun. 287 No.1. No.2. No.3. 484/4

481/4 473/4 511/2 483/8 477 Therefore,the thermometer No.1 rose 35/ degree, in 10minutes,at 112 inch beyond the visible light of the red rays. I might now have gone on to the 5th line; but, so fine a day,with regard to clearness of sky and perfect calmness, was notto be expected often,at this time of the year; I thereforehastened to make a trial of the other extreme of the prismaticspectrum. This was attended with some difficulty, as the illu-mination of the violet rays is so feeble, that a precise terminationof it cannot be perceived. However,as well as could be judged,I placed the thermometers one inch beyond the reach of theviolet rays,and found the result as follows, No.1. No.2. No.3. 48 48 473/4 48 48 473/4 48 471/2 47 481 471/2 47

48 473/4 Here the several indications of the thermometers, two ofwhich,No.1 and 2, were used as variable, while the 3d waskept as the standard,were read off during a time tha lasted12 minutes; but they afford,as may be seen by inspection,noground for ascribing any of their small changes to other causesthan the accidental disturbance which will arise from the motionof the air, in a room where some employment is carried on. I exposed the thermometer now to the line of the very firstperceptible violet light; but so that No. 1 and 2 might again MDCCc. Pp Downloadd from https://royalsocietypublishing.org/on 07 December 2024

288Dr.HERSCHEL's Experiments on the Refrangibility be in the illumination,while No.3 remained a standard. Theresult proved as follows. No.1. No.2. No.3. 48 48 473/4 48π/2 48 473/4 483/4 481/2 473/4 49 48π/2 473/4 Here the thermometer No. 1 rose 1 degree, in15 minutes;and No. 2 rose 1/2 degree, in the same time. From these last experiments, I was now sufficiently persuaded,that no rays which might fall beyond the violet, could haveany perceptible power,either of illuminating or of heating; andthat both these powers continued together throughout the pris-matic spectrum, and ended where the faintest violet vanishes. A very material point remained still to be determined,whichwas, the situation of the maximum of the heating power. As I knew already that it did not lie on the violet side of thered, I began at the full red colour, and exposed my thermometers,arranged on a line, so as to have the ball of No. 1 in the midstof its rays, while the other two remained at the side, unaffectedby them. No.1. No.2. No.3. 481/2 481/2 48 55π/2 481/2 48

551/2 481/2 48

Here the thermometer No. 1 rose 7 degrees, in 10 minutes,byan exposure to the full red coloured rays. I drew back the stand,till the centre of the ball of No. 1 was Downloaded from https://royalsocietypublishing.org/ on 07 December 2024

of the invisible Rays of the Sun. 289 just at the vanishing of the red colour, so that half its ball waswithin, and half without, the visible rays of the sun. No. 1. No.2. No.3. 481/2481/248 551/2 481/2 48

290 Dr.HERSCHEL's Experiments on the Refrangibility order to obtain a true maximum, as the sun was now morepowerful than it had been at that time; for which reason, Icaused the line of termination of visible light, now to fall againjust I2 inch from the centre of the ball; and had the followingresult. No.1. No.2. No.3.

of the invisible Rays of the Sun. 291 inch and a half beyond the red ones, measured upon their pro-jection on a horizontal plane. I have no doubt but that theirefficacy may be traced still somewhat farther. The 5th and 6th experiments shew,that the power of heatingis extended to the utmost limits of the visible violet rays, butnot beyond them; and that it is gradually impaired,as the raysgrow more refrangible. The four last experiments prove, that the maximum of theheating power is vested among the invisible rays; and is pro-bably not less than half an inch beyond the last visible ones,when projected in the manner before mentioned. The sameexperiments also shew, that the sun's invisible rays,in their lessrefrangible state, and considerably beyond the maximum,stillexert a heating power fully equal to that of red-coloured light;and that, consequently, if we may infer the quantity of the effi-cient from the effect produced, the invisible rays of the sunprobably far exceed the visible ones in number. To conclude, if we call ligbt,those rays which illuminateobjects,and radiant beat, those which heat bodies, it may beinquired, whether light be essentially different from radiantheat? In answer to which I would suggest, that we are notallowed,by the rules of philosophizing, to admit two differentcauses to explain certain effects,if they may be accounted forby one. A beam of radiant heat, emanating from the sun,consists of rays that are differently refrangible. The range oftheir extent, when dispersed by a prism, begins at violet-coloured light, where they are most refracted, and have theleast efficacy. We have traced these calorific rays throughoutthe whole extent of the prismatic spectrum; and found theirpower increasing, while their refrangibility was lessened,as far Downloaded from https://royalsocietypublishing.org/on 07 December 2024

292 Dr.HERSCHEL's Experiments, &c. as to the confines of red-coloured light. But their diminishingrefrangibility, and increasing power, did not stop here; for wehave pursued them a considerable way beyond the prismaticspectrum, into an invisible state, still exerting their increasingenergy,with a decrease of refrangibility up to the maximum oftheir power; and have also traced them to that state where,though still less refracted, their energy, on account, we maysuppose, of their now failing density, decreased pretty fast;after which,the invisible tbermometrical spectrum,if I may socall it,soon vanished. If this be a true account of solar heat, for the support ofwhich I appeal to my experiments,it remains only for us toadmit, that such of the rays of the sun as have the refrangibilityof those which are contained in the prismatic spectrum, by theconstruction of the organs of sight, are admitted, under theappearance of light and colours; and that the rest, being stoppedin the coats and humours of the eye, act upon them, as theyare known to do upon all the other parts of our body,by occa-sioning a sensation of heat. Slough,near Windsor, March 17, 1800. EXPLANATION OF PLATE XI. IN WHICH IS GIVEN A VIEW OF THE APPARATUS. AB. The small stand. 1,2,3. The thermometers upon it. C D.The prism at the window. E. The spectrum thrown upon the table, so as to bring thelast quarter of an inch of the red colour upon the stand. Downloaded from https://royalsocietypublishing.org/on 07 December 2024

Downloaded from https://royalsocietypublishing.org/on 07 December 2024 a Philos. Trans.MDCCC.Plate XI.p.2g2.