Question about Herschel experiment which discover Infra red light

In summary, Herschel discovered infrared light by observing the trend of increasing temperature from blue (lowest temperature) to red (highest temperature) in an experiment where he placed a blackened thermometer next to a prism. His goal was to determine the temperature outside the visible red light. However, his findings showed that the highest temperature rise occurred in the infrared region, which has the shortest wavelength. This may seem contradictory to the idea that higher frequency light carries more energy, but it is explained by the fact that the sun emits a larger number of red photons compared to blue photons. This can be seen in Herschel's experiment where the infrared light was more concentrated onto the thermometer, resulting in a higher temperature reading.
  • #1
b612_l_prince
2
0
Hi there, I have a question about his experiment.

Herschel discovered IR by placing the blacken thermometer next to the red light (out from the prism), since he noticed the TREND OF INCREASING TEMPERATURE proceeded from BLUE (lowest temperature) TO RED (highest temperature). So he wanted to find out what the temperature would be just outside visible red light.

So my question is, we always say when frequency of a light is higher (wavelength is shorter), the energy that light carries is higher. However, in his experiment, Herschel found the highest temperature rise is indeed in Infra Red region... shortest wavelength?!

Is there anyone could give me some clues on this "contradiction"? What mistake have I made in having such a contradicting conclusion?

Thanks a lot.


Charlotte

P.S. The details of the experiment can be found at http://coolcosmos.ipac.caltech.edu/cosmic_classroom/classroom_activities/herschel_bio.html
 
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  • #2
While each individual blue photon contains more energy than each individual red photon, the sun makes a whole lot more red photons than blue photons.

- Warren
 
  • #3
thanks warren

thanks Warren for letting me know. I appreciate it. =)
 
  • #4
A more correct answer

The Infrared thermometer is heated the most because the infrared light
is more concentrated onto it. The IR photons are spatially more concentrated by the prism.
Note - Herschel's prism cut-off longward of 2 microns so the the near-IR from 1-2 um is doing the heating.

See
http://home.znet.com/schester/calculations/herschel/index.html
 

1. What is the Herschel experiment?

The Herschel experiment was a scientific study conducted by Sir Frederick William Herschel in 1800. Herschel aimed to measure the temperature difference between different colors of light by using a prism to split sunlight into its component colors and then measuring the temperature of each color.

2. How did the Herschel experiment discover infrared light?

During his experiment, Herschel noticed that the temperature of the colors increased gradually as he moved from violet to red. However, he also noticed that the temperature increased even beyond the red color, where there was no visible light. Herschel concluded that this increase in temperature was due to an invisible form of light, which he called "calorific rays" and is now known as infrared light.

3. Why is the Herschel experiment important in the study of light?

The Herschel experiment was significant because it proved that there are forms of light that are invisible to the human eye. This discovery expanded our understanding of the electromagnetic spectrum and paved the way for further research and advancements in the field of optics and infrared technology.

4. How did the Herschel experiment impact the scientific community?

The Herschel experiment solidified the concept of the electromagnetic spectrum and provided evidence for the existence of infrared light. It also opened up new avenues for research and experimentation, leading to advancements in fields such as astronomy, meteorology, and communications.

5. What are some practical applications of the Herschel experiment's findings?

The discovery of infrared light through the Herschel experiment has led to numerous practical applications in various industries. For example, infrared technology is used in thermal imaging cameras for medical and military purposes, in remote controls for electronic devices, and in heat-seeking missiles for military use. It also helps in studying celestial bodies and their temperatures in astronomy and is used in weather forecasting and climate research.

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