Into Unscientific

"Catch a wave in an electromagnetic field?"

Hearing Xu Yun's words.

Faraday subconsciously turned his head and looked at his good friend William Weber.

Then the two electromagnetism masters thought of something at the same time.

They turned their gazes to the huge galvanized metal plate in the classroom.

different from ordinary visible light.

If there is a wave in the electromagnetic field, it must have the property of being invisible to the naked eye.

This is a truth that children understand. After all, if they could see electromagnetic waves, Faraday and others would have noticed it long ago.

Therefore, the "catch" that Xu Yun mentioned must not be to directly present the electromagnetic wave in front of everyone, but to use a certain phenomenon or reaction as evidence.

Just like Faraday's iron filing experiment:

At that time, he sprinkled a layer of very fine iron filings on a piece of paper, put a magnet under the paper, and then tapped the paper lightly.

As a result, the iron filings that have been shaken are neatly arranged along the magnetic lines from the north pole to the south pole of the magnet.

Faraday thus discovered the concept of magnetic field lines.

So if nothing unexpected

Xu Yun's 'capture' this time is obviously replacing the real thing with phenomena, and there is no surprise in this.

Just what will happen?

Is it a physical reaction?

Or does it mean replacing the invisible with phenomena?

And just as Faraday and the others were thinking, Xu Yun said again:

"Professor Faraday, can we start the experiment now?"

Only then did Faraday come back to his senses, and cast a questioning look at Prince Albert at the side.

Although the uncrowned king of the British peninsula lacks professional knowledge, he is the person with the highest status on the scene after all, and the experiment must obtain his consent before it can start.

Faraday, Prince of Albert, nodded slightly, and said to Xu Yun:

"Please start, student Luo Feng."

Xu Yun said yes, and glanced lightly at Prince Albert from the corner of his eye.

In the few short words just now, Prince Albert paused twice, and the pause was accompanied by swallowing movements.

It is clear.

The stomach and esophageal spasms that eventually led to Prince Albert's untimely death had clearer symptoms.

Albert, as the most famous "husband-in-law" in British history, later generations, especially British medical scientists, have done a lot of research on his condition during his lifetime.

To be sure.

Prince Albert suffered from waist rheumatism, enlarged prostate, stomach cramps and reflux esophagitis during his lifetime.

The last two of them are most likely to be the culprits that led to the death of Prince Albert.

There is no omeprazole in the UK these days, and reflux esophagitis is much higher than later generations in terms of pain and threat.

But Xu Yun hesitated.

He wasn't sure if he should make a move.

Because in the original history of Prince Albert, his attitude towards China was really weird and weird.

First of all, as an interest class, Prince Albert must have enjoyed the dividends that a crow brought to Britain.

But as the uncrowned king of Britain, he himself has never expressed any attitude or instructions to Huaxia.

He did not care about the situation in the East from the beginning to the end, and his focus was mainly on Germany, America, industry and economy during his lifetime.

It seems that the East does not exist at all, and the prime minister of the United Kingdom has always been in charge of the strategy towards China.

In his previous life, Xu Yun asked a friend to help him collect the scanned version of the British resolution on China between 1840 and 1865. He spent more than 700 yuan before and after, but he did not find even a single resolution decided by Albert.

Not to mention good or bad character, this is completely unreasonable from the perspective of a country's decision-makers-any European class, who would ignore China in the 19th century?

But Albert did just that.

It's like you have a stock software that gives you tens of millions of dividends and interest a year, but you never care about this part of the money, and you don't even have the idea of ​​turning on your mobile phone to see how much it rose yesterday.

This is obviously a very, very strange behavior.

Later generations of Jinling University even opened a project on this, studying Prince Albert's attitude towards China, but in the end there was no accurate conclusion.

So Xu Yun really doesn't understand what kind of character this person is.

It would be much easier to deal with if it was a villainous foreign gun team captain like Grant, or a respectable international friend like Lindsay.

Think here.

Xu Yun couldn't help shaking his head, and put this thought behind him.

It's still a long time, let's take a look at it slowly.

The top priority now is to deal with the experiment and connect Faraday's line.

Then he walked to the side of the experimental generator and said to Thomson:

"Mr. Thomson, please draw down all the curtains in the room."

Thomson nodded immediately and said:

"clear."

Swipe la la——

After a while.

All the black curtains in the classroom were drawn down.

In addition, the classroom is located in a remote corner, so the room is not completely dark at this time, at least it can be regarded as the standard of a 'dark room'.

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 has more detailed specifications:

The copper ball remains unchanged, but the length of the copper rod connecting the copper ball is uniformly constant at 12 inches, and the side length of the square zinc plate is 16 inches.

soon.

Zizizi——

As the voltage increased, the spark reappeared.

call out--

Immediately afterwards.

As the light reflected, sparks also appeared on the receiver.

See this situation.

Faraday and the others looked at each other again, a trace of doubt flashed in their pupils.

The phenomenon is still shocking, but it seems

Same as yesterday?

But soon.

Faraday's attention was attracted by something in Xu Yun's hand:

It was a glass tube about the size of a flashlight, and there was 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 to form a loop, and a voltmeter is hung on one end.

Seeing this, Faraday couldn't help standing up, walked to Xu Yun's side, and pointed to the glass pipe:

"Student Luo Feng, what is this?"

Xu Yun glanced at him, raised the glass tube, and explained with a smile:

"It's a chip detector."

"Swarf 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 on the wall.

after awhile.

He looked at Xu Yun with emotion on his face, and said clearly:

"I see. I understand. It's standing waves. Mr. Fat Fish used standing waves, right?"

Xu Yun smiled and nodded.

well known.

As a shining node in the history of physics, the photoelectric effect has many theoretical derivations, but there are only two main points in the conceptual sense.

First of all, it refuted the wave theory of light-it gave 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 photocurrent.

This frequency v0 is called the cut-off frequency, also known as the red limit frequency, the limit frequency.

If the frequency v of the incident light is less than the cut-off frequency v0, no matter how strong the incident light is, the photoelectric effect cannot be produced.

But according to wave optics point of view.

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 leave the cathode.

The second knife cannot explain why there is a cut-off voltage, and it only changes with frequency:

According to the viewpoint of wave optics, the kinetic energy of the 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 the problem of instantaneousness-even if the light is very weak, the response time of the photoelectric effect is still very fast, and it does not change with the light intensity.

From the point of view of wave optics.

At a specific cut-off voltage, the time to generate 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 the 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 that sentence.

The scientific community in 1850 still had too narrow acquaintance with the microscopic field, so Xu Yun did not intend to explain the truth of the entire photoelectric effect at this time.

Only when no one knows the answer can it be called a dark cloud.

He is just an ordinary porter who has done a little work, so he should ask someone else to answer the question.

In addition to the theory of anti-killing fluctuations.

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 not enough to support the electromagnetic wave or the conclusion that "the primary coil electromagnetically oscillates and the secondary coil is induced".

So how did Hertz verify electromagnetic waves?

The answer is the standing wave method.

To put it simply, a standing wave is a wave that does not go away.

Why don't you leave there?

Of course it is between two opposing parallel walls.

A space has three sets of opposite parallel walls, that is, 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=2Acos2π(x/λ)cos2π(t/T).

It is not difficult to see from this equation.

The pitch of the 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 the pitch?

In 1887, Hertz gave the answer with an ingenious design:

He first arranged a secret room, and then designed a geophone based on the principle of a radio wave ring, and used the geophone to detect standing waves.

This detector doesn't display numbers, but can emit sparks depending on the situation:

The wave thing has peaks and troughs, and the flame of the detector is brightest when it is at the peaks and troughs, and there is no flame at 0 values ​​between the peaks and troughs.

From this, the pitch of the standing wave can be obtained by calculating the position where you are standing.

Of course.

Hertz's geophone is relatively primitive and its sensitivity is very low, so Xu Yun made some modifications on the geophone this time:

He made a chip detector.

When the photoelectric effect does not occur, iron filings are loosely distributed.

The entire detector is equivalent to an open circuit, and the ammeter will not display the current.

And once the electromagnetic wave is detected.

The iron filings will come to life, gather into a ball, act as a conductor, and activate the voltmeter.

The closer to the peak or trough, the more iron filings will condense, and the greater the value on the meter will be.

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 any equipment accurate to the femtometer nanoscale, the idea is the most important.

For example, when Xu Yun was in school, there was an experiment that needed to simulate the vibration of spider silk, but he couldn't find equipment with a suitable vibration period for a while.

As a result, a female man took out the X-press stick and the X-protector on the spot, and perfectly simulated the required cycle data through the sponge pad.

That incident became a legend of HKUST for a time, and Xu Yun and the others even mentioned it when they were reunited.

Of course.

Xu Yun and the others haven’t explained something clearly to that girl—afterwards everyone thought about it, and in fact, the practical 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 in the active state, and distributed several detectors prepared by William Whewell to everyone to detect the standing wave.

"The voltmeter here is 0, which is a zero point!"

"Is there anything bigger than mine at 1.7V?"

"...should be gone, 1.7 seems to be the position of the peak and trough."

"1.51.61.7, I found it, my place is a peak area!"

The voices of a group of bigwigs echoed in the room, and soon, the pitch of several standing waves was detected.

"0.26 meters."

Looking at the numerical values ​​after statistical comparison, Faraday touched his chin:

"The distance between two points where the standing wave cancels is half the wavelength, which is nλ/2. Then, if 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.

After these scales are amplified by standing waves, they can be easily measured in the macroscopic world.

In other words.

Xu Yun really 'captured' the electromagnetic wave!

Looking at the value on the paper, he looked at the detector in his hand.

While Faraday was shocked and admiring, he couldn't help feeling a little bit depressed:

Although he already knew that he couldn't compare with Mr. Fat Fish, he never expected that the gap between himself and Mr. Fat Fish would be so big

This experiment designed by Mr. Fat Fish is probably enough for everyone present to recall for a lifetime.

Not to mention according to Xu Yun.

This is just one of the experiments designed by Mr. Fat Fish.

As expected of a figure who can stand alongside Sir Newton.

all in all.

Things have reached this point, the next thing is very simple.

In these years, Hertz has not proposed the concept of the unit of frequency, that is, Hertz.

But the spectrum thing was invented as early as the Mavericks period, but it is still relatively close to the "period" in definition.

The generator designed by Xu Yun is equivalent to an oscillating dipole, which will excite high-frequency oscillations during the occurrence, and the induction coil will be charged at a frequency of 10-100 per second, resulting in a damped oscillation pattern. (I'll try again to see if I can put it in this chapter. Now the review in this chapter is a bit speechless)

Knowing the number of turns and power, the cycle calculation is simple.

So soon.

The two values ​​of wavelength and oscillation period were placed in front of Faraday and others at the same time.

Faraday stared at the value for a long time, finally picked up the pen and started the calculation.

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, this error can basically be ignored for everyone in 1850.

Swish Swish Swish——

Faraday's pen tip moved steadily and quickly across the paper.

He is not very good at mathematics, facing the current amount of calculations, he will more or less feel a little bit strenuous.

A few minutes later.

Faraday finally calculated the last digit.

Just when he was about to breathe a sigh of relief, his brow subconsciously frowned again.

Do not know why.

He always felt that the number on the paper seemed somewhat familiar?

Seeing Faraday's hesitant expression, Xiaomai couldn't help it. This person's thirst for knowledge is even comparable to that of a calf.

I saw him rushing forward to take a few glances, and suddenly let out a light snort:

"2.97969X10^8m/s, this is not"

"The speed of light?!"