Chapter 573 Witness the Miracle! (Part 3)_2

Soon.

Zzz—

As the voltage increased, the spark reappeared.

Whoosh—

Immediately afterward.

With the reflection of light, a spark also appeared simultaneously on the receiver.

Seeing this situation.

Faraday and others exchanged glances, a hint of confusion flashing in their pupils.

The phenomenon was still astonishing, but it seemed to be...

No different from yesterday’s?

But soon.

Faraday’s attention was caught by something in Xu Yun’s hand:

It was a glass tube about the size of a flashlight, containing some black powder inside that looked somewhat like sesame powder.

Outside the glass tube was a wire, with both ends of the wire connected to the ends of the glass tube, forming a circuit, and a voltmeter hanging at one end.

Seeing this, Faraday couldn’t help but stand up, walk over to Xu Yun’s side, and point to the glass tube:

"Luo Feng, what is this thing?"

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

"This is a metal filings detector."

"Metal filings detector?"

Faraday repeated the term several times, suddenly realizing something.

He suddenly raised his head, gazing at the giant galvanized metal plate fixed to the wall.

After a while.

He looked at Xu Yun with a sigh of emotion and said with understanding:

"Ah, I see... I understand, it’s the standing wave, Mr. Feiyu utilized the standing wave, right?"

Xu Yun nodded with a smile.

As is well known.

The photoelectric effect, as a dazzling milestone in the history of physics, has countless theoretical implications, but conceptually, it mainly consists of only two points.

The first is the rebuttal of the wave theory of light—it slashed the major arteries of the wave theory three times.

The first slash is the cutoff frequency.

That is, for certain metal materials, only when the frequency of the incident light is greater than a certain frequency v0 can electrons escape from the metal surface to form a photoelectric current.

This frequency v0 is called the cutoff frequency, also known as the red limit frequency or the threshold frequency.

If the frequency v of the incident light is less than the cutoff frequency v0, no matter how strong the incident light is, the photoelectric effect cannot occur.

And according to the viewpoint of wave optics.

No matter what the frequency is, as long as the light is strong and the time is long, electrons can obtain enough kinetic energy to escape from the cathode.

The second slash cannot explain why there is a cutoff voltage, which only changes with frequency:

According to wave optics, the kinetic energy of electrons escaping the cathode should be proportional to the light intensity and duration of exposure.

Therefore, the maximum kinetic energy of electrons should change with light intensity and exposure time, meaning the cutoff voltage should vary with light intensity.

The third slash is the problem of instantaneity—even when the light is very weak, the response time of the photoelectric effect is still very fast and does not vary with light intensity.

According to wave optics.

At a specific cutoff voltage, the time to produce the photoelectric effect should be inversely proportional to the light intensity.

But in fact, in the photoelectric effect, regardless of light intensity, as long as the cutoff frequency and cutoff voltage requirements are met, the time it takes to produce the photoelectric effect is on the order of 10e-14s.

Still, it has to be said.

The scientific community of 1850 had too narrow an understanding of the microscopic domain, so Xu Yun did not intend to fully explain the truth of the photoelectric effect at this time.

No one knows the answer, which is why it’s called a riddle.

He’s just an ordinary porter who did a little trivial work, the solving part should be left to someone wiser.

Besides refuting wave theories.

The other significant conceptual meaning of the photoelectric effect is that it verified the existence of electromagnetic waves.

It’s crucial to know.

If we look solely at the phenomenon of the photoelectric effect itself, it is actually insufficient to support the conclusion of electromagnetic waves... or rather, "primary coil electromagnetic oscillation, secondary coil induced" conclusion.

So how did Hertz validate electromagnetic waves?

The answer is the standing wave method.

To put it simply, a standing wave is a wave that stubbornly refuses to leave.

Where does it stubbornly stay?

Of course, it’s stuck between two opposing parallel walls.

A space has three sets of opposing parallel walls, which are your front and rear, left and right, and top and bottom.

Its essence is the resonance phenomenon of space, with the comprehensive equation as y=y1+y2=2Acos2π(x/λ)cos2π(t/T).

From this equation, it’s not hard to see.

The nodes of the standing wave are equal to n times the half-wavelength, so as long as the node spacing is known, the original wavelength can be calculated.

Thus, the problem of validating electromagnetic waves can be attributed to another new aspect:

How to determine the node spacing?

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

He first arranged a closed room and then designed a detector composed based on the principle of a wave ring to detect the standing wave.

This detector does not display numbers but can emit sparks based on different conditions:

Wave has peaks and troughs, and the detector’s flame is the brightest at the peaks and troughs, and there is no flame at the 0 value between the peak and the trough.

By measuring the position of the observation, the node spacing of the standing wave can be obtained.

Of course.

Hertz’s detector was quite primitive and had low sensitivity, so Xu Yun made some modifications to the detector this time:

He made a metal filings detector.

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

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

But once electromagnetic waves are detected.

The metal filings become active, clump together, acting as a conductor to activate the voltmeter.

The closer to the wave crest or trough, the more the metal filings clump, and the greater the value shown on the voltmeter.