Chapter 261 Is electromagnetic wave light?
The speed of electromagnetic waves is approximately the same as the speed of light.
With the words of wheat.
Faraday was stunned for a moment, and then he suddenly slapped his forehead with a crisp "pop".
That’s it
No wonder this number feels familiar to me.
2.97969X10^8m/s. Isn’t this almost the same as the previously measured speed of light? !
But
Why is this happening?
To know.
In this era, the scientific community has a relatively clear understanding of mechanical waves:
It is the transfer of momentum and energy in matter caused by the propagation of disturbances.
At the same time, mechanical waves can be divided into two types: longitudinal waves and transverse waves.
Such as waves along strings, sound waves, etc., and of course mixed waves.
In addition to different types of waves, the speed of propagation also differs from wave to wave.
For example, the speed of sound waves is 340 meters per second. The person who measured this value is called Durham, a British man.
In 1708, he observed the cannon with the naked eye and measured the speed of sound at about 343 meters per second at 20 degrees Celsius.
As for the person who measured the speed of sound in water, it was Colaton.
He was in Geneva, the name of the place. Through a precise small experiment on Lake Geneva, he calculated the speed of sound in water to be 1435 meters/second.
In addition, there are sine waves and even light waves. These values now have measurement methods and results.
In Faraday's view.
Electromagnetic waves originate from electric fields and magnetic fields, and the oscillation frequency of the electric field is inherently high.
Coupled with the comparison of phenomena, it is naturally unlikely that the wave speed of electromagnetic waves is a low value.
But this "unlikely to be a low value" means that it reaches the sky at tens of kilometers per second, which is faster than the seismic wave speed guessed by John Michel in 1760.
But according to actual measurement results, the speed of electromagnetic waves is actually close to the speed of light?
From the perspective of Faraday or every big guy present, they can realize what this similarity means.
Coincidences of this magnitude basically do not exist in physics. Substances with similar key values on ultra-high scales must have some relationship with each other.
Seeing that Faraday was silent, Joule hesitated for a moment and asked:
"Student Luo Feng, could it be that we made an error in the measurement process?"
Xu Yun glanced at him.
As a person from later generations, Xu Yun can somewhat understand Joule's thoughts.
It is normal to have doubts in your heart when faced with phenomena that can impact your three views.
Xu Yun shook his head slightly and explained:
"Mr. Joule, as you saw in the testing session just now, we collected no less than fifty sets of pitch data in total."
"Although there may still be deviations in the values calculated from this, this deviation will at most lead to a difference in a few decimal places. It is still very accurate in terms of the concept of 'magnitude'."
"The other thing is."
As Xu Yun spoke, he pulled out the earliest classical wave equation from the table, pointed at the equation and continued:
"We can actually start with the wave equation and calculate the speed of electromagnetic waves from a purely mathematical perspective."
Upon hearing this, Faraday and others quickly turned their attention to the equation.
A few seconds passed.
Newman, who had never had any acting roles, suddenly snapped his fingers and drew a circle on μ0ε0 with a pen:
"Yes, we can inversely deduce the wave speed from the equation. Oh, I should have thought of this a long time ago!"
Mentioned previously.
The wave equation of the electric field is ▽B=μ0ε0 (B/t).
The wave equation of the magnetic field is ▽E=μ0ε0 (E/t).
Comparing the wave equations of the electric field and the magnetic field, you will find that their forms are exactly the same - it is just that E and B are interchanged.
This shows that the waves existing in the two are completely consistent in speed. At the same time, comparing the speed term of the classical wave equation, it is not difficult to find another situation:
The speed of electromagnetic waves can be deduced from the wave equation of the electromagnetic field.
That is.
V=1/√￣μ0ε0.
Among them, μ0 is the absolute dielectric constant, and its value is 4π×10^-7m·kg/C.
ε0 is the vacuum dielectric constant, with a value of 8.854187818×10^-12Cs/kg·m.
The unit of the former can be written as N/A, and the latter can be expressed as F/m.
Just follow normal history.
Be it Farah or Ampere.
These units would not be formally defined until the International Electrical Congress in 1881.
But the same curl as before.
The scientific community in 1850 had already recognized this concept, but the expression was still Cs/kg·m for the time being.
Just like the coulomb, the unit of capacitance, it was also a value defined at the International Electrical Congress in 1881, but it had been used badly before that.
The reason why such a conference was held in 1881 was mainly because American and Asian countries did not have a complete system in this regard, so such a formal meeting was used to characterize the units.
Among them, Asian countries mainly refer to neon, which is related to the Meiji Restoration, so I won’t go into details here.
By the way.
Seven electrical measurement units were defined at that meeting, namely:
Coulombs, Amperes, Volts, Ohms, Farads, Henrys and Siemens.
Of course.
Seeing this, some students may ask:
With the level of science and technology in 1850, how on earth could those data be calculated in a vacuum?
This is actually somewhat similar to the question raised by a reader when Xu Yun was writing novels in his previous life, "Can the values in 1850 be so accurate?"
The root cause of these two problems still lies in the inherent cognitive barriers - many people think that 1850 and now are two eras, and it is great to be able to calculate 10x10=100.
This is actually a very serious mistake.
Actually.
The year 1850 can already be regarded as the approaching node of modern science.
Within this node, many areas are not as primitive as everyone thinks.
For example, vacuum measurement.
In fact, as early as 1643, Galileo's student Torricelli made the world's first device to measure gas pressure.
He experimentally confirmed that atmospheric pressure is equivalent to the pressure of 760mm of mercury, which is 7.6×104Pa, and pioneered the quantitative measurement of the degree of vacuum.
Before 1850, Bourden, the man who invented the Bourdon tube, also invented the deformation vacuum gauge.
Otherwise, why do you think Wheat can calculate the speed of light in vacuum from Maxwell's equations?
There is an insurmountable barrier between 1850 and 2022, there is no doubt about it.
But this does not mean that that era was a pure primitive society without any bright spots.
This is the same as today's online novels. In 2022, more than one work will be published with an average subscription of 100,000. This was something that was unthinkable in 2012 - at that time, the average subscription of the head was only more than 10,000 Just twenty thousand.
But can you say that the online writing works in 2012 have no highlights?
Obviously not.
Works such as "Covering the Sky", "Swallowing", "Eternal Life" and "Mortal" are still classics even from the perspective of 2022.
Each era has its own limitations, but it also has its shining points.
His eyes returned to reality.
I thought of V=1/√￣μ0ε0, then the next step is very simple.
"V=1/√￣4π×10^-7m·kg/CX8.854187818×10^-12Cs/kg·m"
Such a complex calculation process was naturally left to Wheat:
"So V=√￣8.987552x10^16m/s"
"The final answer is 2.9979X10^8m/s!"
The value calculated by Wheat is the speed of light in vacuum. In addition, Xu Yun and others' measurements have some errors, so it is very normal for there to be some differences after the decimal point.
“2.9979X10^8m/s”
Faraday repeated this number, and while he was filled with emotion, another thought came to his mind unexpectedly:
If you want to teach at Cambridge University for a long time, you will probably have to ask Prince Albert for some nitroglycerin regularly
Then he took a deep breath, looked at Xu Yun, and asked:
"Classmate Luo Feng, from this point of view, are light and electromagnetic waves the same thing?"
Xu Yun nodded decisively. He was about to say something, but stopped when he was about to say it.
In an instant.
Many thoughts passed through his mind.
He hesitated for a moment, and what he was supposed to say was replaced by another sentence:
"Yes, Mr. Faraday, based on the research of Fat Fish Ancestor, he finally came to a conclusion."
"That is electromagnetic wave, which is a special frequency of light."
Friends who have studied physics in the second year of high school should all know this.
Light is actually a type of electromagnetic wave and belongs to a proper subset of electromagnetic waves.
In layman's terms, it is a certain frequency, that is, electromagnetic waves within the wavelength range, which we call light.
For example, humans are only a part of the primates. If humans are compared to light, then electromagnetic waves are all primates.
Of course.
These are just some basic concepts, and it will become very complicated if you go deeper.
For example, electromagnetic waves can be said to propagate without a medium, or they can be said to propagate using space-time as a medium. For example, space-time fluctuations are open strings in string theory.
Therefore, changes in the curvature of space-time caused by gravity can affect light. Some people even believe that the ether that people have been looking for is actually space-time itself, etc.
In particular, some civil sciences like to put forward some weird opinions in this regard.
It is said that someone sent an email to the Academy of Sciences last year, expressing the hope of going to the tokamak for observation.
Others can die in the morning and die in the evening, but this person can die in a second after hearing the word in the morning.
all in all.
Regardless of which of the deeper theories is correct, the concept that light is a proper subset of electromagnetic waves is still OK.
But after thinking again and again, Xu Yun decided to put forward a contrary statement:
Electromagnetic waves are a type of light.
After all, as far as the current situation is concerned, the character design of 'Fat Fish' is really a bit too perfect.
Countless examples in history tell us that a perfect ‘god’ does not exist, and problems can occur.
Everyone will make mistakes, and even have black spots that are criticized by others.
In the long run, this is not a good thing.
So Xu Yun simply imitated Xiao He and cast a black halo on "Fat Fish".
In fact, Xu Yun had considered this issue before.
However, it is indeed difficult to find an experimental target that can be used as a black spot but that does not have such a big impact on the development of scientific history.
Unfortunately, electromagnetic waves are a very good choice.
The dispute over the properties of electromagnetic waves and light has always remained in the theoretical realm, and the practical aspects should be as they are.
Even if you say that light and electromagnetic waves are another thing that does not exist - for example, they are both called "fishing girls", it will not have much impact in practical operations.
At the same time in a few years.
When JJ Thomson discovered cathode rays from experiments, the scientific community would probably have doubts about Xu Yun's statement.
Once the truth that light is electromagnetic waves is discovered, many people will be able to breathe a sigh of relief:
Oh, it turns out Mr. Fat Fish can make mistakes too.
Pattern.jpg.
Of course.
At this time, Faraday did not know Xu Yun's thoughts.
After hearing Xu Yun's words, a slight strange feeling flashed through his heart, and he quickly accepted the explanation.
After all, judging from the phenomena currently understood, there is really no obvious difference between light and electromagnetic waves.
Later, Xu Yun, Faraday and others used equipment such as polarizers to verify the characteristics of electromagnetic waves, and found that they also have the characteristics of refraction, reflection and polarization.
At this point, all that's left is the finishing touch.
Faraday took out a piece of parchment and wrote his final conclusion on it:
[It has been verified that electromagnetic waves are a special kind of light].
Faraday and others then summarized the experimental results again and prepared to officially announce the relevant content at the next academic conference.
So far.
Xu Yun's first wave of sexy operations at Cambridge University officially came to an end.
I think from now on, I will never encounter anything more exciting than this
Bar?
Faraday and Joule Kirchhoff both came out. Xu Yun really couldn't think of anything bigger than this battle.
Well, absolutely impossible!
If there was, he would be willing to eat that ax again on the spot!
Half an hour later.
After packing up the equipment, Xu Yun took Mai and returned to dormitory 302.
As soon as I entered the house.
Xu Yun took off his scarf and lay down on the bed.
Tell the truth.
The two days of experiments seemed to go very smoothly, but for Xu Yun, the pressure on his shoulders was really quite big.
After all, even one detail error in the entire process may have an irreversible impact on the results.
Fortunately, relying on the character accumulated through hard work and renewal in my previous life, I successfully passed this test.
And just when Xu Yun was lying on his back.
A curtain of light appeared in front of him for a long time.
[It has been detected that the first ring of the Wallfacer mission has been completed, the mission evaluation and the second ring mission are being generated] (End of this chapter)