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Origins of spectroscopy

Temperature of rainbows

Spectroscopy begins with a simple observation we can all relate to:
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However, there is much more to a rainbow than meets the eye, literally. Human eyes can only see a tiny slice of the full color spectrum that make up rainbows. This was discovered due to heat.

Infrared light

In 1800 William Herschel noticed that light passing through colored filters would transfer different amounts of heat. This lead to a fascinating experiment designed to determine the energy of different colors by placing a thermometer across the colors of the spectrum and observing  changes in temperature.
The experiment led to an unexpected discovery. Herschel noticed that the highest temperature was beyond red where there was no visible light. He went on to find that these “heat rays” could be transmitted, reflected and absorbed just like visible light. This portion of the spectrum is known as infrared (“below red”) radiation.

UV light

One year later Johann Ritter discovered more invisible light on the violet side of the rainbow. He found that that photographic paper exposed to the rainbow will darken towards violet light (which is why we use red lightbulbs when working with unexposed film). When he put the paper beyond the visible violet light it quickly turned black due to ultraviolet (UV) radiation. UV radiation is responsible for the burns we experience when skin is exposed to direct sunlight.
Image Credit: NASA
These simple discoveries were only the tip of the iceberg. Over the next 130 years investigators made a series of discoveries leading to the modern understanding of the electromagnetic spectrum. You can think of this spectrum as the “full rainbow” as compared with the smaller spectrum visible to our naked eyes.
Image Credit: NASA

Introduction to the electromagnetic spectrum

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  • hopper cool style avatar for user ☣Ƹ̵̡Ӝ̵̨̄Ʒ☢ Ŧeaçheя  Simρsoɳ ☢Ƹ̵̡Ӝ̵̨̄Ʒ☣
    So can we tell just the compound, not how much of the different parts, or can we determine the exact chemical makeup of a substance with spectroscopy?
    (14 votes)
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  • blobby green style avatar for user theschouwstras
    what does an absorption spectrum show
    (2 votes)
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  • purple pi purple style avatar for user M Syahman Samhan
    The energy of electromagnetic waves increases as the wavelength decreases. Knowing that red's wavelength is larger than blue's, why red is hotter than blue in Herschel's experiment?
    (2 votes)
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    • leaf blue style avatar for user Reed
      Infrared light is basically just heat radiation. The redder the light, the more heat comes from it. This is why heat lamps are red, and why thermal imaging night vision cameras look at the red side of the color spectrum.
      (1 vote)
  • blobby green style avatar for user Joseph Suganthan
    Are cosmic rays electromagnetic?
    (1 vote)
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  • piceratops ultimate style avatar for user Kavin Sankar
    What is spectra all about. Like what do you have to study for optical spectra.
    (1 vote)
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  • leafers ultimate style avatar for user Himalay
    Why is the temperature in infra-red region warmer than that in visible region?
    The frequency of visible light is greater than that of infra-red rays. So, the energy of infra red rays will be lesser (E=hv :-Plank's relation) and hence the temperature too.
    (1 vote)
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  • piceratops ultimate style avatar for user Aaron Travass
    I have heard a lot about Wi-Fi( the Wi-Fi router and so ). So what exactly is Wi-Fi?Can someone explain it to me in detail.
    (0 votes)
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    • leafers seed style avatar for user seanbcampbell
      Wi-fi uses radio waves, which are, as you can see here, on the electromagnetic spectrum. Computers use modems to translate digital information to electrical signals, which is sent over radio waves. (As electricity is part of electromagnetic radiation, which this is, this makes sense.) It can be sound, video, or digital signals. These signals can be represented in any number of ways, such as voltage levels or frequencies. For radios, which use AM or FM, the amplitude (strength) or frequency of the radio wave is what is changed to represent data. With Wi-Fi, multiple waves are sent at once, making its efficiency much higher. I hope this makes sense; I sort of learned as I went along with this answer.
      (1 vote)