What is Infrared Radiation & Electromagnetic Spectrum? - [4]

Summary

In this episode of '10 Minute Science,' viewers are introduced to the concept of infrared radiation, a type of electromagnetic wave associated with heat. The video explains how infrared radiation was discovered by William Herschel, who found that the temperature increased beyond the red spectrum, indicating the presence of invisible light. It also covers the electromagnetic spectrum, the relationship between wavelength, frequency, and energy, and how infrared radiation is used to detect heat, even in the dark. The script concludes by pondering the unknown aspects of the universe that remain undiscovered due to our limited sensory and technological capabilities.

Takeaways

• 🌡️ Infrared radiation is associated with heat and is radiated by all objects, even those not visibly glowing.
• 👀 Infrared light is invisible to the human eye but can be detected with specialized cameras or instruments.
• 🏠 The script uses images to demonstrate how infrared radiation can reveal heat leaks in a house and the relative temperature of different areas.
• 🤒 Infrared radiation can be used to detect fever in humans, as an elevated body temperature emits more infrared radiation.
• 🔬 The electromagnetic spectrum includes a range of wavelengths, with infrared lying just beyond the red visible light.
• 🌈 The visible light spectrum is just a small part of the entire electromagnetic spectrum, which also includes radio waves, microwaves, and gamma rays.
• 🔍 The discovery of infrared radiation by William Herschel was accidental, as he noticed higher temperatures beyond the red light when using a prism and thermometer.
• ⚫ The black body curve illustrates how objects radiate energy at different wavelengths according to their temperature, with infrared often being more prevalent than visible light.
• 🔆 Even though violet light has higher energy photons, the sun emits fewer violet photons than red or infrared, affecting the temperature readings in Herschel's experiment.
• 🔬 Quantum mechanics tells us that the energy of a photon is related to its frequency, with higher frequencies corresponding to higher energies.
• 🌌 The script ends with a thought-provoking question about the unknown aspects of the universe that we may be unaware of due to our limited sensory and technological detection capabilities.

Q & A

What is infrared radiation?

Infrared radiation is a type of electromagnetic radiation that we associate with heat. It is invisible to the human eye but can be detected with special cameras and is emitted by all objects with a temperature above absolute zero.

How can infrared radiation be visualized?

Infrared radiation can be visualized using special cameras that are sensitive to infrared wavelengths. These cameras can create images that represent the relative heat of objects, with colors such as red indicating hotter areas and blue indicating cooler areas.

What does the color in an infrared image represent?

In an infrared image, different colors represent the relative temperature of the objects being imaged. Reddish colors indicate hotter areas, while bluer and yellow colors represent cooler areas.

How was infrared radiation discovered?

Infrared radiation was discovered by William Herschel in 1800. He found that there was a type of invisible light beyond the red end of the visible spectrum that caused a thermometer to register higher temperatures than the visible light.

What is the electromagnetic spectrum?

The electromagnetic spectrum is a range of all types of electromagnetic radiation, arranged by wavelength or frequency. It includes radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, and gamma rays.

Why can't we see infrared radiation with our eyes?

We can't see infrared radiation with our eyes because the chemistry of our eyes is sensitive only to a specific range of wavelengths known as the visible spectrum. Infrared wavelengths are longer than the red light that marks the limit of our visible range.

What is the relationship between wavelength, frequency, and energy of electromagnetic waves?

The relationship between wavelength, frequency, and energy is such that as the wavelength gets longer, the frequency gets lower and the energy of the photons decreases. Conversely, as the wavelength gets shorter, the frequency gets higher and the energy of the photons increases.

How does the sun emit different frequencies of light?

The sun emits light across a wide range of frequencies. However, it does not emit all frequencies equally. The distribution of frequencies emitted by the sun follows a pattern known as a blackbody curve, which has a peak and then gradually decreases on either side.

Why does a thermometer measure higher temperatures in the infrared region compared to violet light, even though violet photons have higher energy?

Although violet photons have higher energy than infrared photons, the sun emits fewer violet photons than it does red or infrared photons. The temperature measured by a thermometer is influenced by the total energy from all photons hitting it, not just the energy of individual photons.

What is the significance of the discovery of infrared radiation in relation to our understanding of the universe?

The discovery of infrared radiation expanded our understanding of the universe by revealing that there is more to the electromagnetic spectrum than what is visible to the human eye. It also highlighted the fact that objects emit radiation based on their temperature, which is crucial for technologies such as thermal imaging and understanding celestial bodies.

What are some applications of infrared technology that we use today?

Infrared technology is used in various applications today, including thermal imaging for detecting heat signatures, night vision for military and security purposes, remote controls for electronics, and in astronomy for studying stars and other celestial objects.

How can the concept of infrared radiation be used to detect fever in humans?

Infrared radiation can be used to detect fever in humans by measuring the heat emitted by the body. When a person has a fever, their body temperature increases, and so does the amount of infrared radiation they emit. Specialized infrared cameras can capture this increased radiation, indicating a fever.

What is the connection between infrared radiation and the study of dark matter and dark energy?

The connection between infrared radiation and the study of dark matter and dark energy is that they all represent aspects of the universe that are not directly observable with our senses or current instruments. The discovery of infrared radiation, which was initially undetected, has led to the exploration of other phenomena that may be present but currently beyond our detection capabilities.

Outlines

00:00

🌡️ Introduction to Infrared Radiation

The video begins with an introduction to '10 Minute Science,' a series that explores scientific topics in a concise manner. The main focus of this episode is infrared radiation, its definition, discovery, and relevance. Infrared radiation is associated with heat and is invisible to the human eye. The host promises to explain how it can be visualized and why it is significant. The explanation begins with a look at images that represent different temperatures through color variations, indicating heat loss through windows and good insulation in a house. The concept is further illustrated by showing how a radiator and a person with a fever emit infrared radiation, which is detectable even when visible light is not.

05:00

🔬 The Electromagnetic Spectrum and Infrared Discovery

This paragraph delves into the electromagnetic spectrum, explaining the range of wavelengths that make up different types of electromagnetic radiation, from radio waves to gamma rays. Infrared (IR) radiation is positioned just beyond the red light in the visible spectrum. The discovery of infrared radiation is attributed to William Herschel, who in the early 19th century, observed that there was a region of the spectrum beyond red light that was particularly warm. His experiments involved using a prism to disperse sunlight and a thermometer to measure the temperature increase at different points in the spectrum. Herschel's accidental discovery led to the understanding that infrared radiation is a form of electromagnetic radiation that we cannot see but can detect as heat.

10:06

🔍 Herschel's Experiment and Infrared Detection

The script recounts William Herschel's experiment in detail, where he used a prism to split sunlight into a spectrum and measured the temperature at various points. Herschel found that the region beyond red light, now known as infrared, registered a higher temperature than any of the visible colors. This indicated the presence of an invisible form of light that had a warming effect. The host also shares a personal anecdote about replicating Herschel's experiment during a science fair, which confirmed the presence of infrared radiation beyond the visible red light, as it registered a higher temperature than the visible spectrum colors.

15:07

⚫️ The Black Body Curve and Sun's Radiation

The explanation continues with the concept of a black body curve, which describes how objects at a certain temperature emit radiation across the electromagnetic spectrum. The sun's radiation is used as an example to illustrate that not all frequencies are emitted equally; some are more intense than others. The sun emits more infrared radiation than ultraviolet light, despite the fact that individual ultraviolet photons have higher energy than infrared photons. This discrepancy is due to the lower number of high-energy photons compared to the higher number of lower-energy ones. The sun's radiation is also discussed in terms of the spectral irradiance, showing that the sun emits a wide range of wavelengths, with visible light being only a small part of the sun's total output.

20:08

🌌 Infrared Radiation and the Universe's Hidden Aspects

The final paragraph emphasizes that infrared radiation is a form of electromagnetic radiation like any other part of the spectrum, but with a longer wavelength. It reiterates the accidental discovery of infrared by Herschel and its association with heat, explaining that all objects above absolute zero temperature emit infrared radiation. The host concludes by pondering the unknown aspects of the universe that we may be unaware of due to our limited sensory and technological detection capabilities, hinting at phenomena like dark matter and dark energy. The video ends with an encouragement for viewers to continue exploring and learning about science.

Keywords

💡Infrared Radiation

Infrared radiation is a type of electromagnetic radiation that is associated with heat. It is invisible to the human eye but can be detected with special cameras or sensors. In the video, infrared radiation is the main theme, as it is discussed in the context of being emitted by all objects, regardless of their temperature, and its discovery by William Herschel. The script uses examples such as the infrared images of a house, where different colors represent varying temperatures, and a person with a fever, whose body emits more infrared radiation compared to others.

💡Electromagnetic Spectrum

The electromagnetic spectrum is the range of all possible frequencies of electromagnetic radiation. It is organized by wavelength, from the longest (radio waves) to the shortest (gamma rays). In the video, the spectrum is discussed to explain where infrared radiation fits in relation to visible light and other types of radiation. The script mentions that infrared lies just beyond the red light in the visible spectrum and that it is part of a broader range of wavelengths that includes radio waves, microwaves, and gamma rays.

💡Wavelength

Wavelength is the distance over which a wave's shape repeats. It is a fundamental property of any wave, including those in the electromagnetic spectrum. The video script explains that wavelength is inversely related to frequency, with longer wavelengths corresponding to lower frequencies and shorter wavelengths to higher frequencies. The concept is used to differentiate between types of electromagnetic radiation, such as radio waves having long wavelengths and gamma rays having short wavelengths.

💡Frequency

Frequency refers to the number of oscillations or cycles a wave completes in a given time period, typically measured in Hertz (Hz). In the context of the video, frequency is discussed in relation to wavelength and energy. The script explains that as the frequency of electromagnetic waves increases, so does their energy, which is why gamma rays, with very high frequencies, are high-energy photons.

💡Photons

Photons are elementary particles that are the quantum units of light and other electromagnetic radiation. The video script mentions photons to explain that electromagnetic waves, including infrared radiation, are not just continuous waves but also come in discrete packets of energy. This concept is central to quantum mechanics and is used to describe the transfer of energy in the form of light.

💡William Herschel

William Herschel was a British astronomer who is credited with the discovery of infrared radiation. In the script, Herschel's discovery is recounted as an accidental finding when he noticed that the area beyond the red light in the spectrum produced by a prism was warmer to the touch than the other colors. This led him to conclude that there was an invisible form of light that we now call infrared.

💡Calorific Rays

Calorific Rays is the term originally used by William Herschel to describe the type of invisible light he discovered beyond the red spectrum, which was associated with heat. The script mentions this historical term to provide context to the discovery of infrared radiation and how Herschel linked the sensation of warmth with this new type of radiation.

💡Black Body Curve

A black body curve is a theoretical representation of the electromagnetic radiation emitted by a perfect absorber of light (a black body) at a given temperature. In the video, the black body curve is introduced to explain how different wavelengths of light are emitted at different intensities depending on the temperature of the source. The script uses this concept to clarify why the Sun emits more infrared radiation than ultraviolet radiation, despite the latter having higher energy photons.

💡Spectral Irradiance

Spectral irradiance refers to the power of electromagnetic radiation per unit area per unit wavelength or frequency. In the script, the term is used in the context of plotting the black body curve to illustrate how the Sun emits different amounts of energy at different wavelengths. This concept helps to explain why certain wavelengths, like infrared, can be detected as warmer even if they have lower energy photons.

💡Thermometer

A thermometer is a device used to measure temperature. In the video script, Herschel's use of a thermometer to measure the temperature of different colors of light is highlighted as a key part of his discovery of infrared radiation. The script describes how Herschel blackened the bulb of the thermometer to absorb more radiation, leading to the accidental discovery that the region beyond red light was warmer, indicating the presence of infrared radiation.

💡Quantum Mechanics

Quantum mechanics is a fundamental theory in physics that describes how the physical world operates at the smallest scales, such as the level of atoms and subatomic particles. The script briefly mentions quantum mechanics in the context of explaining the energy of photons and the electromagnetic spectrum. It is the underlying principle that helps to understand why different wavelengths of light have different energies and how they interact with matter.

Highlights

Infrared radiation is associated with heat and is radiated by all objects around us.

Infrared radiation is invisible to the human eye but can be detected with special cameras.

Different colors in thermal images represent relative temperatures, with red indicating hotter areas.

Infrared radiation can reveal heat leakage through windows and good insulation in a house.

A sick person with a fever can be identified through the infrared radiation emitted by their body.

The discovery of infrared radiation is attributed to William Herschel in the late 18th century.

Herschel discovered infrared by measuring temperatures of different colors of light from the sun.

The electromagnetic spectrum includes a range of wavelengths from radio waves to gamma rays.

Infrared radiation falls just beyond the red visible light in the electromagnetic spectrum.

The energy of a photon is related to its frequency, with higher frequencies having more energy.

Infrared radiation is associated with lower energy photons due to its longer wavelengths.

The sun emits more infrared photons than ultraviolet ones, despite their higher energy per photon.

Herschel originally called infrared radiation 'calorific rays', relating it to heat.

Infrared radiation is not a 'heat ray' but an electromagnetic wave like visible light and other spectrum types.

Every object above absolute zero temperature radiates energy, including infrared.

Infrared radiation can be detected even when an object is not emitting visible light.

The video concludes with a thought-provoking question about undiscovered aspects of the universe that we may be ignorant of due to our current detection limitations.

Transcripts

hello welcome back to 10 minute science where  we take a topic we dissect it and we learn about  

something amazing in 10 minutes or less but  remember that's plus or minus 12 additional  

minutes so what we have today we're going to  learn about the concept of infrared radiation  

what is infrared radiation and also how was it  discovered and why do we care I promise it'll  

be worth your time to stick with me till the end  so infrared radiation is the radiation that we  

associate with heat of a body so everything  around you is radiating these invisible Rays  

we call infrared Rays or infrared radiation let's  take a look at a few pictures in the first picture  

here we have a house now the different colors  here are telling us the relative temperature  

the relative the relative temperature hot or cold  the reddish colors are the hotter aspects and the  

Bluer and the yellow are the cooler areas now  we can see that the uh the walls there near the  

windows are actually red and that means that we  can see a lot of heat coming through the windows  

and that means basically heat is leaking through  the windows it's not a very good insulator around  

the windows but we see up around the walls and  the other areas near the top of the image that  

it's not quite so red and that means that there's  a lot of really good insulation there keeping the  

heat in the house so anywhere we see red we see  heat uh leaking out of the house now it seems  

kind of amazing that you can see heat what we're  seeing is the infrared radiation coming from that  

heat you can see that actually the chimney on top  of the house you can see a little bit of yellow  

and a little bit of red there as well because  of course you know the chimney leaks heat out  

that's what it's supposed to do all right let's  take a look at image number two where we have the  

interior of our house we have a window and at  the bottom of the image we have a radiator to  

heat the house up in the winter time now we can  see that the window is blue which means that the  

windows are quite cold because the outside air  temperature is cold and when we look underneath  

the window we see that the radiator the little uh  the white area down there is actually red which  

means it's radiating a lot of heat so there's  there's a heater going on it's very hot and so we  

see that as red so red is hot blue is cold now in  the third little thing we're going to look at here  

who have some people walking by we have cameras  that can sense the infrared radiation and we can  

see that most of the people in this image are you  know not too hot so we have some some uh some of  

the clothes are actually uh cooler the skin is a  little bit warmer but there's one person in this  

Frame that's actually looks red hot and that  person actually is sick with a fever so when  

the temperature of the body gets elevated we can  actually see it in the form of infrared radiation  

coming off the body so the one person there  is sick right and then the fourth picture here  

uh we can see the head of this woman here and  the hair and you can see the hair itself is not  

that hot so it's bluish more blue color but the  skin itself is is much warmer so the skin is hot  

there so how can we see heat that's what we want  to come come to the understanding of and also how  

is this even discovered because the story behind  it is quite interesting all right so in order to  

go any farther we need to take the kid gloves off  and talk about the answer to this thing we'll get  

to the discovery of it in a minute but we're  going to talk about the what we know to be true  

today so what we have is a spectrum we call it an  electromagnetic spectrum you see the waves up here  

we'll talk about it in a second here now what you  can see with your eyes is a very small sliver of  

this thing that which we call the electromagnetic  magnetic Spectrum you can see over here we have  

the purple or violet or indigo blue and then we  have the greens and the yellows and then the Reds  

but these are the only uh uh wavelengths we'll  talk about wavelength in a second that we can  

see from the electromagnetic spectrum and that is  just because of the chemistry of our eyes our eyes  

have photoreceptors which are we have chemicals  in our eyes that react to certain energy photons  

and so in that range uh where they're sensitive  to then we can when a photon hits we can trigger  

a reset we can see the photon essentially but if  a photon energy we're going to talk about photons  

in a second a little more Falls outside of this  visible bandwidth there this is visible range  

then the chemistry is not triggered so we can't  see infrared but we can build machines cameras  

that are sensitive to infrared and the other uh  the other aspects of the spectrum now I'm going  

to do a whole video on the Spectrum but just  in a nutshell you notice you have radio waves  

now we have this wave up here notice that the  wave is very stretched out we say it has a very  

long wavelength over here right and in fact these  are this is you know very very long this is meter  

so this is you know this is a hundred meters here  here's in the thousands of meters over here these  

radio waves can be very very long then we have am  and F M waves that you can use for the radio Wi-Fi  

microwave is actually a centimeter wavelength  and then we have infrared IR which Falls just  

on the other side of red here and then we have  the visible spectrum now we start to get into  

shorter wavelength electromagnetic waves and then  on the other side of violet we have ultraviolet  

so flanked on each side of the visible spectrum  on the one side of red we have infrared and on  

the other side of violet we have ultraviolet I  know you've heard of ultraviolet because that's  

what we have to protect ourselves from the Sun  from getting a sunburn now on the other side  

of that we have x-rays which are high energy  and gamma rays which are even higher than that  

now the one thing I want to point out because  it's going to become important later in the  

lesson is and I'm going to do an entire lesson  on the electromagnetic magnetic Spectrum another  

day but for now just know that it consists of  waves which can differ in wavelength so we have  

long waves over here and when I mean wavelength  I mean these are a waves that oscillate right and  

in space and in time and so the wavelength which  we call Lambda is the distance over which a wave  

begins to repeat so notice it goes up down and it  begins to repeat again that's one wavelength and  

it's literally measured in meters okay so these  waves over here are very long this is like a this  

is 100 meters this is like a thousand meters over  there and even longer and then we have centimeters  

which are in your microwave so the microwave oven  has a little centimeter length waves and then we  

have visible which are basically this is measured  in uh billionths of a meter so we'll talk about  

that in a second I have another slide and then  we have even shorter and shorter and shorter  

but notice that as the wavelength gets shorter  because the wave is actually getting shorter  

then the frequency which is on the top gets is  getting bigger so frequency is how much something  

is oscillating and you can see over here it's not  oscillating very much or very fast so to speak  

but over here these gamma rays and x-rays are  oscillating very very fast so the wavelength and  

the frequency are they go opposite of each other  as the wavelength gets longer the frequency gets  

uh or the wavelength gets bigger the frequency  gets lower and lower because it's not oscillating  

much and as the wavelength it's very very small  the frequency gets very very fast all right and  

the other thing that we're going to talk about  a little bit later is that as the frequency gets  

higher and higher and higher the energy of each of  these photons because electromagnetic waves come  

in packets that we call photons we discovered that  along with the Advent of quantum mechanics these  

waves do not just travel like waves in the ocean  they come in packets like little little buckets  

that hit the hit your eye and hit the detector  which we call a photon of course there's an  

oscillating aspect to it but they come in packets  we call photons and because these are oscillating  

faster these have what we call higher energy so  as you look at this chart this is lower energy  

medium energy and higher energy and over here  the gamma arrays are the highest energy photons  

you may have heard of gamma radiation or x-ray  radiation that's the highest energy photons  

that we know about there but all of these are  basically different flavors of the same thing  

they are flavors of electric and magnetic fields  which are oscillating we call electromagnetic  

waves all right I have one more chart to drill  that home here this is basically the same thing  

it's the same thing as what was there just with  numbers showing that the visible spectrum Falls  

from 400 nanometers of wavelength remember  a nanometer is a billionth of a meter so 400  

billionths of a meter very very small wavelength  but this is a larger wavelength over here it's  

the same picture as this it's just kind of hard  to read these numbers here and this is so small  

here and what the exponents is very difficult  so we often talk about wavelengths of light  

in terms of nanometers so you see the smaller  wavelength here bigger one going this direction  

all right so now that we know that the visible  light that we can see is only a tiny fraction  

of everything that's out there that we can't see  uh but in in uh the time when infrared light was  

discovered we didn't know of anything that existed  other than the visible light okay now anything uh  

that we say uh on the other side of here we call  it infrared and on the other side of violet we  

call ultraviolet said that and uh we want to  talk about now how it was discovered because  

the discovery of infrared light is actually really  really fascinating so there was a scientist named  

William Herschel he lived from 1738 to 1822 and  he was doing astronomy so we had a telescope and  

he was actually looking at the sun or measuring  the Sun that not a not a uh I don't advise you to  

do that because you can damage your eyes but  he was using filters on his telescope to try  

to to see what kind of light the sun was actually  emanating and coming and sending to Earth and what  

he thought he was seeing through his telescope  when he would put different filters in front  

of the telescope is he thought that uh he was  sensing that the red light when he would isolate  

the red light from the telescope he thought that  it felt warmer to his touch than the blue light  

for instance when he would put the blue filter  in front of the telescope so he started getting  

curious about the temperature of the different  current uh wavelengths of light that are being  

sent and are what what is the temperature  distribution which one is hotter and which  

one is colder right so we wanted to investigate  that now in order to investigate it further what  

he did is he put the telescope away and he or I  guess he focused it through a telescope took the  

light from the sun and passed it through a prism  now you can see what's going to happen we've all  

done this we know that when we take sunlight which  is all of this stuff here and we put it through a  

prism it breaks it up into the Spectrum right  we can see the different colors there and what  

he did is he tried to measure the temperature of  the different colors so he would literally take a  

thermometer and he would take the bulb of it and  bulb of the thermometer and Blacken it with black  

paint the reason he did black paint is because it  was known that black colors absorb more radiation  

and you know that as well today and what he would  do is he would physically put this thermometer  

here and here and here and here and here and then  uh measure the temperature of the of a different  

light coming from the Sun and what he figured  out is that this violet color was cooler and as  

he would move the thermometer this way towards  red it got warmer and warmer and warmer here  

and then just by accident see what he was trying  to do was do a controlled experiment so he would  

put one thermometer in the purple and he would  put one thermometer outside of the spectrum  

just as a control to see what the Ambient Air  Temperature was out here so he would put one  

thermometer in here and one thermometer here but  we know now that on the other side of this uh red  

is infrared so what is the thermometer on the  outside was doing was measuring the temperature  

of the infrared photons that he couldn't see with  his eyes but but that were that was hitting his  

uh his detector here his thermometer and what he  figured out is that the infrared thermometer was  

actually getting hotter than any of these other  colors and hotter than the air temperature so he  

knew that there had to be some sort of invisible  light that he couldn't sleep with his eye that  

was hitting this thermometer and that's kind of  amazing it was discovered totally by accident  

infrared and then later we learned that there's  even more than infrared that exists out of there  

all right now he originally called this infrared  light just just as a historical interest he called  

it calorific Rays now you can think of calorific  being similar to calorie and which kind of means  

heat and so that's kind of where that comes from  we don't call it calorific Rays anymore we call  

it infrared radiation because it's right on the  other side of red and the visible spectrum now as  

chance would have it when my daughter was doing  the science fair years ago we reproduced this  

experiment I actually did it in the backyard took  a box took sunlight refracted it through a prism  

we could see the rainbow and we would carefully  measure the temperature of the different colors  

and then also the infrared and I'm going to  write down the numbers that we got even though  

it's not that super important but I think it's  it's it's useful to see so what we saw is that  

for the violet color we measured 80 degrees  Fahrenheit now apologize for Fahrenheit I  

don't like the Fahrenheit temperature scale it's  the only thermometer I had available that day so  

that's why we use that there and then when we get  over here to Yellow over here we were measuring  

around 84 degrees Fahrenheit and just a smidge  higher it was very hard to read the difference  

between yellow and red here but when we put the  thermometer outside of red right here in the  

infrared region we actually measured 86 degrees  Fahrenheit so we sort of reproduced herschel's  

experiment which is the whole point of you know of  why we did it and we could see that that was true  

all right now I've actually done a similar video  to this in the past and a lot of students sent  

me comments because I told you that we got  the lowest temperature on Violet and then  

medium temperatures over here and infrared was  the highest temperature but then those of you  

that know a little bit about quantum theory you  know that the energy of a photon of an individual  

photon is what we call HF this is just Planck's  constant this is planks constant it's just a  

number so don't worry about what it is right now  it's just a number times F which is the frequency  

of the wave so you can see that that these very  long uh these long wavelengths this is very  

low frequency so because it's a low frequency  it's a low energy Photon so this is low energy

low energy Photon but as we go this way  higher and higher frequency higher and  

higher frequency higher and higher frequency  the frequency is getting higher this is just  

a number so the energy of every photon is  higher as the frequency gets higher and it  

makes sense when you think about it because  the wiggling is very very very very fast so  

it makes sense that it would be a higher  energy so over here we have high energy

high energy Photon so the same thing is true  of the visible this is higher energy than  

this because the frequency here is higher than  the red and higher than the infrared so let me  

ask you a question if we know the energy of the  Violet should be higher than the energy of the  

red if we know that to be true from math from  quantum mechanics which we know is true it's  

a very accurate Theory then when I measured the  temperature why did I measure a low temperature  

here and a high temperature here it doesn't  make any sense well there's one more piece  

of the puzzle again I'll do a totally separate  video later but one more piece of the puzzle  

that we want to talk about to understand that  and that is how does the sun actually broadcast  

all of this energy to Earth because it doesn't  broadcast all the frequencies the same that's  

the punch line so what we can measure uh and  we can measure this in the lab we can measure  

that we can calculate it also with quantum  mechanics if we plot the wavelength this is  

Lambda the wavelength in nanometers right uh and  we can on this axis we can call that the spectral  

uh irradians I'm going to put irr for irradians  because the units don't really matter I could  

write it's watts per and there's some other units  it doesn't matter so much what it turns out is  

everything in the universe including the Sun at  a certain temperature radiates according to what  

we call a black body curve it looks something  like this it goes up to some Peak and then it  

drags down gradually on the other side like this  so you see this is a plot of wavelength this is  

very low wavelength long wavelength light like  what's over here very long wavelength and then  

here we have a a very uh I'm sorry I said that  backwards we have very short wavelength light  

which is over here short wavelength line over here  and very long wavelength like like radio waves and  

things like that over here very long wavelengths  over here now what I want to do is I want to put  

two little X's right here one right here and one  right here and I'm going to draw a little dotted  

line down here and this is from the Sun our sun  whoops I can spell Sun correctly son like this  

and I'll draw a little dotted line down here right  what we have is this region here is the visible  

right and then on the other side of visible higher  

energy is what we call ultraviolet  and then over here this is infrared

but don't forget that as you go farther Beyond  infrared just like over here like this is infrared  

right here you have microwaves and radio waves  and all this other stuff so you have all kinds  

of radio waves way over here as well when you  get long wavelength but the point is is the  

entire visible spectrum that the sun radiates  to Earth it's not radiating all frequencies  

this this is the same amount right the uh uh the  shortest wavelength that we have right here the  

shortest wavelength which is the the purple or  the Violet I guess I should say this is violet  

and this is red because it's longer wavelengths  longer wavelength is red and then you get to  

infrared right so notice what's going on even  though every Photon of violet light has more  

energy than every Photon of red light that is true  however you can see according to the graph the sun  

is sending a lot less Violet photons to Earth  than red and then Infrareds are on the other  

side of it but infrared is still higher than  the violet light so I'm going to say that one  

more time because I've probably got thousands of  comments about this it is true that violet light  

violent photons and UltraViolet photons have  a higher energy because of this equation right  

Planck's equation higher energy per photon than  all of the red in the infrared light that's true  

every Photon for a violet and UltraViolet is more  energy however the sun is not sending as many of  

those photons to the Earth and when I measure the  temperature of these different colors what you're  

doing is it's all the photons are hitting it and  and the energy is going in there and then making  

the thermometer do it it's thing and you can read  it but if there's not that many of these photons  

the temperature is not going to be as high so even  though the data is sort of completely backwards  

than what we know reality to be the point is  Herschel put his thermometer outside of this  

region and he was able to detect like that he  couldn't see at all so that is the last thought  

I want to leave you with infrared radiation is  associated with heat because everybody in the  

universe even if it's not reflecting any actual  light even if it's in the dark like a human  

being in the dark totally dark room if you could  look at them in the infrared you're going to see  

infrared radiation why because I'm again I'll do  a whole nother video on it but everybody in the  

universe at any temperature above zero is going  to be radiating energy and some of that energy  

is going to be infrared even if it's not radiating  any visible light it will always be able to you'll  

always be able to detect some photons other than  visible photons uh there so for instance if you  

put a a poker in the uh in the fire the campfire  if you make it red hot and hold it up you see  

the red color it's radiating red but it's also  rating radiating infrared but as it cools down  

right as it cools down then you don't see as  much of the red color but it's still hot so in  

an infrared camera we're still going to see some  infrared light there even though the visible isn't  

radiating as much because the infrared photons are  are not being able to be detected by your eye all  

of this energy all of it is coming from atoms and  the electrons going up and down in their orbits  

and when the electrons fall back into an orbit  they radiate a photon away so even if it's not  

visible to you the infrared radiation is coming  because electrons can fall in orbits and emit  

an infrared Photon in the wavelength range that  we've outlined here just beyond uh just beyond the  

um the 700 nanometer range those will be the  infrared photons so even if the the poker is  

not emitting visible light which would be higher  energy it can still be radiating infrared light  

so that's why we associate infrared with heat it  doesn't mean the infrared is like a heat ray or  

a different kind of Ray or something different  it's still an electromagnetic wave just like  

light just like ultraviolet just like radio waves  just like microwaves just like gamma rays you see  

I can go on and on just like Wi-Fi right it's  still a photon of electromagnetic radiation the  

only difference is the reason we associate it  with heat is because if something is warm but  

not visible like that poker that is still hot from  the from the fire but not glowing it can still be  

uh radiating infrared photons over here but maybe  we're not seeing the visible because this entire  

curve as the temperature of the object changes  this curve shifts around so maybe maybe we're  

not seeing any of the infrared Photon anymore but  we can we're not seeing any more of the visible  

photons anymore but we can still be seeing  the infrared photons so the takeaway here is  

infrared light is light just like any other color  of the spectrum it just has a longer wavelength  

and red light and the way it was discovered was  absolutely by accident by William Herschel now  

the last thought I'll leave you with is what other  aspects of our universe are we completely ignorant  

of just because we can't detect it with our senses  or our computers or our instruments you know we're  

wrestling with questions like dark matter dark  energy that we don't interact with we don't see  

or interact with dark matter it must be around us  but we don't interact with it that's the problem  

we don't sense it because it it must not interact  with normal matter the same way that light for  

instance interacts with matter light bounces off  of everything okay but we know about that because  

we can sense it what other things are out there  that we can't even sense that we're completely  

ignorant of just because we don't have the proper  equipment on our body or in our computers to  

detect it that's what I want to leave you with for  our last thought there so thanks for taking this  

ride with me on infrared radiation I encourage  you to learn more about amazing science Concepts