Chapter 260 Witness the miracle! (Part 2)
"Capturing waves in electromagnetic fields?"
Hearing Xu Yun's words.
Faraday subconsciously turned his head and looked at his good friend William Webb.
Then the two electromagnetic experts thought of something at the same time.
They turned their attention to the huge galvanized metal plate in the classroom.
It is different from ordinary visible light.
If there really is a wave in the electromagnetic field, then it must have properties that cannot be observed by the naked eye.
This is a truth that even children understand. After all, if they could see electromagnetic waves, Faraday and others would have noticed it long ago.
Therefore, what Xu Yun refers to as "catch" cannot be directly showing electromagnetic waves in front of everyone, but using a certain phenomenon or reaction as evidence.
Just like Faraday’s original iron filings experiment:
At that time, he sprinkled a layer of very fine iron filings on a piece of paper, placed a magnet under the paper, and then gently tapped the paper.
As a result, the vibrated iron filings were neatly arranged along the magnetic lines from the north pole to the south pole of the magnet.
Faraday discovered the concept of magnetic lines of force.
So if nothing unexpected happens
Xu Yun's 'capture' this time was obviously based on phenomena instead of real objects, and there would definitely be no surprise in this regard.
But what will happen?
Is it a physical reaction?
Or do we mean to replace the invisible with phenomena?
While Faraday and others were thinking, Xu Yun spoke again:
"Professor Faraday, can we start the experiment now?"
Faraday finally came back to his senses and cast a questioning look at Prince Albert beside him.
Although the uncrowned king of the British Peninsula is somewhat lacking in professional knowledge, he is the person with the highest status on the scene after all, and his consent must be obtained before the experiment can begin.
Prince Albert nodded slightly to Faraday and said to Xu Yun:
"Please start, classmate Luo Feng."
Xu Yun said yes and glanced at Prince Albert gently from the corner of his eye.
In these few words, Prince Albert paused twice, and the pauses were accompanied by swallowing movements.
It's obvious.
The stomach and esophageal spasms that eventually led to Prince Albert's untimely death already had clearer symptoms.
Albert is the most famous 'brother-in-law' in British history. Later generations, especially British medical scientists, have done a lot of research on his illness during his lifetime.
That's for sure.
Prince Albert suffered from lumbar rheumatism, prostatic hypertrophy, gastric spasms and reflux esophagitis during his lifetime.
The last two of them are most likely the culprits that caused Prince Albert's death.
Omeprazole is not available in the UK these days, and reflux esophagitis is much more painful and threatening than later generations.
But Xu Yun was a little hesitant.
He wasn't sure whether he should take action.
Because in Prince Albert's original history, his attitude towards China was so strange and weird.
First of all, as an interest class, Prince Albert must have enjoyed the dividends that Yicrow brought to Britain.
But as the uncrowned king of Britain, he himself has never expressed any attitude or instructions to China.
He never paid attention to the situation in the East from beginning to end. During his lifetime, his focus was mainly on Germany, America, industry and economy.
It is as if the East does not exist at all, and the person responsible for China strategy has always been the British Prime Minister.
In his previous life, Xu Yun asked his friends to help collect scanned versions of the British resolutions against China from 1840 to 1865. He spent more than 700 yuan, but he did not find even one resolution decided by Albert.
Not to mention the quality of character, this is completely unreasonable from the perspective of a national decision-maker - who among any European class would ignore China in the 19th century?
But that's exactly what Albert did.
Just like you have a stock software that gives you tens of millions in dividends and interest a year, but you never care about this part of the money, and you don't even have the thought of turning on your mobile phone to see how much it rose yesterday.
This is obviously a very, very strange behavior.
Later Jinling University even opened a subject on this and studied Prince Albert's attitude towards China, but in the end there was no accurate conclusion.
So Xu Yun really didn't understand what kind of character this person was.
If it were Grant, the heinous captain of the foreign rifle team, or Lindsay, a respectable international friend, it would be much easier to deal with it.
Think of this.
Xu Yun couldn't help but shook his head and put this idea to the back of his mind.
It’s still a long time, so let’s observe it slowly and then talk about it.
The top priority now is to handle the experimental matters and tie up Faraday's line.
Then he walked to the experimental generator and said to Thomson:
"Mr. Thomson, please pull down the curtains in the room."
Thomson nodded immediately and said:
"Understood."
Brush la la——
After a while.
All the black curtains in the classroom were lowered.
In addition, the classroom is in a remote corner, so the room is not pitch dark at this time, it can at least be regarded as a "dark room" standard.
Xu Yun checked the equipment one last time, and then pressed the switch of the equipment.
Compared with yesterday's experiment, the generator prepared by Xu Yun today is more precise in specifications:
The copper balls remain the same, but the length of the copper rods connecting the copper balls is uniformly constant at 12 inches, and the side length of the square zinc plate is 16 inches.
soon.
Zizzi——
As the voltage increased, sparks appeared again.
Phew——
Immediately afterwards.
As the light reflects, sparks appear on the receiver.
See this situation.
Faraday and the others looked at each other again, a trace of doubt flashing in their pupils.
The phenomenon is still shocking, but it seems
No different from yesterday?
But soon.
Faraday's attention was attracted by something in Xu Yun's hand:
It was a glass tube the size of a flashlight, with some black powder inside, which looked a bit like sesame powder.
There is a wire outside the glass tube, and the two ends of the wire are connected to the two ends of the glass tube correspondingly, forming a loop, with a voltmeter hanging on one end.
Faraday couldn't help but stand up when he saw this, walked to Xu Yun, and pointed at the glass pipe:
"Classmate Luo Feng, what is this?"
Xu Yun glanced at him, raised the glass tube, and explained with a smile:
"This is a metal chip detector."
"Metal chip detector?"
Faraday repeated the word several times and suddenly thought of something.
He suddenly raised his head and looked at the huge galvanized metal plate fixed to the wall.
After a while.
He looked at Xu Yun with emotion and said clearly:
"That's it. I understand, it's a standing wave. Mr. Fat Fish used the standing wave, right?"
Xu Yun smiled and nodded.
As everyone knows.
As a shining node in the history of physics, the photoelectric effect has numerous theoretical derivatives, but in a conceptual sense there are only two main points.
First of all, it refuted the wave theory of light - it struck three blows to the main artery of the wave theory.
The first cut is the cutoff frequency.
That is to say, for a certain metal material, only when the frequency of the incident light is greater than a certain frequency v0, electrons can escape from the metal surface to form a photocurrent.
This frequency v0 is called the cut-off frequency, also called the red limit frequency and the limit frequency.
If the frequency v of the incident light is less than the cut-off frequency v0, then no matter how strong the incident light is, the photoelectric effect cannot be produced.
From the perspective of wave optics.
No matter what the frequency is, as long as the light is strong and the time is long, the electrons can gain enough kinetic energy to escape from the cathode.
The second reason is that it cannot explain why the cut-off voltage exists and only changes with frequency:
According to the perspective of wave optics, the kinetic energy of electrons leaving the cathode should be proportional to the light intensity and irradiation time.
Therefore, the upper limit of electron kinetic energy should change with light intensity and irradiation time, that is, the cut-off voltage will change with light intensity.
The third knife is a problem of instantaneity - even if the light is very weak, the reaction time of the photoelectric effect is still very fast and does not change with the light intensity.
According to the wave optics point of view.
At a specific cut-off voltage, the time to produce the photoelectric effect should be inversely proportional to the light intensity.
But in fact, no matter what the light intensity is in the photoelectric effect, as long as the requirements of cut-off frequency and cut-off voltage are met, the generation time of the photoelectric effect is on the order of 10e-14s.
But still the same sentence.
In 1850, the scientific community's understanding of the microscopic field was still too narrow, so Xu Yun was not prepared to explain the truth of the entire photoelectric effect clearly at this time.
No one knows the answer, so it can be called a dark cloud.
He was just an ordinary porter who did a small job, so I'd better ask someone else to answer the question.
In addition to the anti-kill wave theory.
Another conceptual significance of the photoelectric effect is to verify the existence of electromagnetic waves.
To know.
If we only look at the photoelectric effect phenomenon itself, it is actually not enough to support the conclusion that electromagnetic waves or "the primary coil electromagnetic oscillations, the secondary coil is induced".
So how did Hertz actually verify electromagnetic waves?
The answer is the standing wave method.
To put it simply, a standing wave is a wave that doesn't move.
Why are you staying there and not leaving?
Of course it lies between two opposing parallel walls.
A space has three sets of opposing parallel walls, namely front and back, left and right, and up and down.
Its essence is the resonance phenomenon of space. The comprehensive equation is y=y1+y2=2Acos2π(x/λ)cos2π(t/T).
It is not difficult to see from this equation.
The pitch of a standing wave is equal to n times the half-wavelength, so as long as the pitch is known, the original wavelength can be calculated.
In this way, the problem of verifying electromagnetic waves can be attributed to another new link:
How to determine pitch?
In 1887, Hertz gave the answer with an exquisite design:
He first arranged a secret room, and then designed a detector based on the principle of a radio wave ring, and used the detector to detect standing waves.
This detector won't display numbers, but it can emit sparks depending on the situation:
Waves have crests and troughs. The flame is brightest when the detector is at the crest and trough, and there is no flame at the 0 value between the crest and the trough.
By measuring where you are standing, you can get the pitch of the standing wave.
Of course.
Hertz's detector is relatively primitive and has low sensitivity, so Xu Yun made some modifications to the detector this time:
He built an iron filing detector.
When the photoelectric effect does not occur, the iron filings are loosely distributed.
The entire detector is equivalent to a circuit break, and the meter will not display current.
And once electromagnetic waves are detected.
The iron filings will become active and clump together, acting as a conductor and activating the voltmeter.
The closer to the peak or trough of the wave, the more iron filings will condense, and the value on the meter will be larger.
In this way, it is undoubtedly much clearer and more accurate than naked eye observation.
In a sense.
This is also the most attractive part of the subject of physics.
Sometimes you don’t need equipment accurate to the femto-nanometer scale, the idea is the most important.
For example, when Xu Yun was in school, there was an experiment that needed to simulate the oscillation of spider silk, but he could not find equipment with a suitable oscillation period.
As a result, a female man took out the X-press stick and X-protector on the spot, and perfectly simulated the required cycle data through the sponge pad.
That incident became a legend at the University of Science and Technology, and Xu Yun and others later mentioned it during their classmates' reunion.
Of course.
There was something that Xu Yun and the others had not made clear to the girl - then everyone thought about it and found that using a razor is similar
Ahem, let’s get down to business.
The idea is clear, and the rest is very simple.
Xu Yun kept the generator activated, divided the several detectors prepared by William Whewell to everyone, and started to detect the standing waves.
"The voltmeter here is 0, which is a zero value point!"
"Is there anything bigger than me at 1.7V?"
". There should be no more. 1.7 seems to be the location of the peak and trough."
"1.51.61.7, found it, this is a peak area!"
The voices of the big guys echoed in the room, and soon the pitches of several standing waves were detected.
"0.26 meters."
Looking at the numerical values after statistical comparison, Faraday touched his chin:
"The distance between the two points where the standing wave cancels is half the wavelength, which is nλ/2. Then calculated in this way, the wavelength of the electromagnetic wave is"
"6.5×10^-7m?"
Xu Yun nodded.
There are actually two main spectral lines of the photoelectric effect, one is 6.5×10-7m, and the other is 4.8×10-7m.
These scales can be easily measured in the macroscopic world after being amplified by standing waves.
In other words.
Xu Yun really 'captured' electromagnetic waves!
He looked at the values on the paper and then at the detector in his hand.
While Faraday was shocked and amazed, he could not help but feel a little sad and decadent:
Although he already knew that he could not compare with Mr. Fat Fish, he never expected that the gap between him and Mr. Fat Fish would be so big
This random experiment designed by Mr. Fat Fish is probably enough for everyone present to remember for a lifetime.
Not to mention according to Xu Yun's statement.
This is just one of the experiments designed by Mr. Fat Fish.
He is worthy of being ranked alongside Sir Isaac Newton.
all in all.
Once things have reached this point, the next thing is very simple.
These days, Hertz has not yet proposed the concept of frequency unit, which is Hertz.
But the spectrum thing was invented as early as the Mavericks period, but the definition is still closer to a 'cycle'.
The generator designed by Xu Yun is equivalent to an oscillating dipole. During the generation, it will stimulate high-frequency oscillations. The induction coil will be charged at a frequency of 10-100 per second, producing a damped oscillation pattern. (I'll try again if I can put it in this chapter. The review mentioned in this chapter is a bit speechless now)
Knowing the number of turns and power, calculating the period is simple.
So it's quick.
The two values of wavelength and oscillation period were placed in front of Faraday and others at the same time.
Faraday stared at the values for a long time, then finally picked up his pen and began to calculate.
The frequency of electromagnetic waves is the same as the oscillation frequency of the wave source, and the wavelength is related to the refractive index of the medium.
Although the refractive index in air is different from that in vacuum, for everyone in 1850, this error was basically negligible.
Swish Swish Swish——
Faraday's pen tip crossed the paper steadily and quickly.
He, who is not very good at mathematics, would find it somewhat difficult to face the current amount of calculations.
After a few minutes.
Faraday finally calculated the last digit.
Just when he was about to breathe a sigh of relief, his brows subconsciously frowned again.
Don't know why.
He always felt that the number on the paper seemed a bit familiar?
Seeing the hesitation on Faraday's expression, Xiaomai on the side couldn't help it. This man's thirst for knowledge was even comparable to that of a calf.
I saw him leaning forward and looking at it for a few times, and suddenly let out a light sigh:
"2.97969X10^8m/s, this is not"
"The speed of light?!" (End of Chapter)