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 electromagnetic waves could be seen, Faraday and others would have noticed it long ago.
Therefore, what Xu Yun refers to as "catching" 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.
This is how Faraday discovered the concept of magnetic lines of force.
So if nothing unexpected happens
Xu Yun's 'capture' this time is obviously using phenomena instead of real objects, so there will 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?"
Only then did Faraday come back to his senses and cast an inquiring 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 is clear.
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.
What is certain is that.
Prince Albert suffered from lumbar rheumatism, prostatic hypertrophy, gastric spasm and reflux esophagitis during his lifetime.
The last two of them are most likely the culprits that led to the death of Prince Albert.
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 or not.
Because in Prince Albert's original history, his attitude towards China was really strange and weird.
First of all, as an interest class, Prince Albert must have enjoyed the dividends that Yiwu has 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.
Let alone good or bad character, this is completely unreasonable from the perspective of a country's decision-makers. 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 think about turning on your mobile phone to see how much it rose yesterday.
This is obviously a very, very strange behavior.
Jinling University in later generations even opened a subject for this purpose 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 threw 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 thread.
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:
"clear."
Brush la la
After a while.
All the black curtains in the classroom were lowered.
In addition, the classroom is located 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 remains constant at 12 inches, and the side length of the square zinc plate is 16 inches.
soon.
sizzling
As the voltage increased, sparks appeared again.
call out
Immediately afterwards.
As the light reflects, sparks also 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, and a voltmeter is hung at 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 awhile.
He looked at Xu Yun with emotion and said clearly:
"I see, I understand, it's a standing wave. Mr. Fat Fish made use of the standing wave, right?"
Xu Yun smiled and nodded.
As we all know.
As a shining node in the history of physics, the photoelectric effect has numerous theoretical derivation directions, but in a conceptual sense there are actually only two main points.
First of all, it refutes the fluctuation of light, saying that it severely stabbed the main artery of the fluctuation three times.
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 intensity of 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 the light intensity and irradiation time, that is, the cut-off voltage will change with the light intensity.
The third knife is a transient problem. 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.
From the perspective of wave optics.
At a specific cut-off voltage, the time for the photoelectric effect to occur 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 it’s 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 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 your front and back, left and right, and up and down.
Its essence is the resonance phenomenon of space, and the comprehensive equation is y=y1+y2=2aos2πos2π.
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 based on different situations:
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 gather into a ball, 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 aspect 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 a massage stick and a protective device on the spot, and perfectly simulated the required cycle data through a 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. Later, everyone thought about it and realized that actually 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 several detectors prepared by William Whewell to everyone, and started detecting the standing waves.
"The voltmeter here is 0, which is a zero point!"
"Is there anything bigger than me at 1.7v?"
"It should be gone. 1.7 seems to be the location of the peak and trough."
1.61.7, found it, this is a peak area!"
The voices of a group of big shots 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"
"6.5x10^-7m?"
Xu Yun nodded.
There are actually two main spectral lines of the photoelectric effect, one is 6.5x10-7m, and the other is 4.8x10-7m.
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 experiment casually designed by Mr. Fat Fish is probably enough for everyone present to remember for a lifetime.
Not to mention what Xu Yun said.
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 excite high-frequency oscillations, and the induction coil will be charged at a frequency of 10-100 per second, producing a damped oscillation pattern.
Knowing the number of turns and power, calculating the period is very simple.
So it's very fast.
The two values of wavelength and oscillation period were placed in front of Faraday and others at the same time.
Faraday stared at the numerical 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 not the same as that in vacuum, for people 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.
A few minutes later.
Faraday finally calculated the last digit.
Just when he was about to breathe a sigh of relief, his brows subconsciously frowned again.
Do not know why.
He always felt that the number on the paper seemed a bit familiar?
Seeing Faraday's hesitant expression, Xiaomai beside him couldn't help it. This man's thirst for knowledge was even comparable to that of a calf.
I saw him leaning forward to look at it for a few times, and suddenly let out a soft sigh:
"2.97969x10^8m/s, this is not"
"The speed of light?!"
－－－－－－Digression－－－－－
I haven’t asked for a monthly ticket for a long time. Can you call me for a monthly ticket? It’s not doubled at the end of the month!!!