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Chapter 15: Chapter 15: This Freaking Works Too?

By the time Jiang Yang returned to the main office with Zheng Hua, over an hour had passed.

A circle of teachers had already gathered around Li Dong’s desk.

Even teachers from the Chinese and English departments next door had come over to see the spectacle.

”This kid writes so fast. He doesn’t even pause.”

”Is he even getting them right?”

”Who knows? But it sure looks like he knows what he’s doing.”

When the teachers saw Zheng Hua arrive, they quickly cleared a path.

”Leader Zheng is here!”

Zheng Hua ignored their greetings and walked straight up behind Li Dong.

First, he sized up the student.

He was wearing a standard school uniform, his hair was a bit long, and he had a rather clean-cut appearance.

Just then, Li Dong turned to the second page and began the fill-in-the-blank questions.

Zheng Hua’s gaze fell upon the test paper.

After a simple glance, he drew in a sharp breath.

Li Dong had already finished all the multiple-choice questions at the beginning.

And...

Zheng Hua quickly scanned a few of the more difficult problems that had left an impression on him.

Question one, correct.

Question five, the equivalent resistance of that complex circuit. He chose B. Correct!

Question twelve, the stopping potential in the photoelectric effect. He chose D. Also correct!

”This...”

Zheng Hua was starting to feel unnerved.

’This speed, this accuracy... even last year’s provincial first-place winners were probably no better than this.’

What he found even more incredible was the method Li Dong was using to solve the problems.

Li Dong wasn’t stubbornly grinding away at every single problem like an ordinary student.

When he encountered an optics question about the ”Fresnel lens,” he paused for only two seconds before decisively skipping it.

He had already determined that the problem would involve a large number of tedious non-spherical geometric approximation derivations.

And the very next question was about the ”time dilation effect in special relativity.”

SWOOSH!

Li Dong didn’t even glance at his scratch paper.

His brain was like a high-speed computer, completing the Lorentz transformation in an instant.

He wrote the time increment in the observer’s frame of reference directly on the line, having even mentally mapped the direct result for a typical coefficient like v = 0.8c.

’This kid...’ Zheng Hua understood.

Li Dong was selective about the problems he solved.

For any problem involving the core concepts of mechanics, electromagnetism, or modern physics, he was lightning-fast and brutally efficient.

But when faced with the ”grunt work”—problems that purely demanded computational power—he made a tactical retreat.

This showed that his framework of knowledge was exceptionally clear; he knew the difference between the ”essence of the physics” and ”mathematical complexity.”

In truth, Zheng Hua was still underestimating Li Dong.

It wasn’t that he was afraid of the calculations; he simply hadn’t learned that particular topic yet. He refused to waste a single second on blind trial-and-error in an unfamiliar area.

At that moment, the school bell rang again.

It was the third period.

Li Dong instinctively stopped writing and looked up at Old Yang.

”Teacher Yang, class has started...”

”You keep going. Don’t worry about anything else.”

Old Yang’s tone was uncharacteristically firm.

”This is my class. I’m excusing you.”

Although Old Yang didn’t teach physics, his expertise was likely the highest among everyone present.

The prestige of Beijing Normal University was nothing to scoff at. Besides, if it weren’t for that whole mess in the past, Old Yang would have long been known to people as a scientist by now.

So, naturally, he could understand the problems. Li Dong was doing exceptionally well, and he also wanted to see what final score Li Dong could achieve.

Li Dong paused for a moment, then nodded at Old Yang and buried his head in his work once more.

By now, a thin layer of sweat had beaded on Li Dong’s forehead.

It was from sheer exhaustion.

The second half of this test had an astonishingly large calculation load.

But the more problems he solved, the more excited he became.

The feeling was like a long-distance chess match against the test’s creator.

The test creator had set one trap after another, laying out a series of mazes.

But he, wielding the sharp swords gifted to him by Newton, Joule, and Einstein, cut a path through all obstacles.

Jiang Yang, standing nearby, couldn’t help but lean in and whisper to Zheng Hua.

”Leader Zheng, is... is there a problem with his work?”

Zheng Hua couldn’t be bothered with him.

’A problem?’

’It’s a huge problem!’

’This kid’s problem-solving method is even slicker than the official answer key!’

Finally, Li Dong turned to the last page.

Question 26.

This was the final, capstone problem of the entire test, the legendary ”weeder” question.

[As shown in the figure, an insulated cylinder is divided into two parts, A and B, by an insulated piston. Part A is filled with 1 mol of an ideal gas, while part B is a vacuum. A light spring with a spring constant k connects the piston to the bottom of the cylinder. The system is initially in equilibrium. The gas in A is now slowly heated by a heating wire. Find the relationship between the gas’s entropy change, ΔS, and the piston’s displacement, x.]

The difficulty of this problem lay in its combination of the first law of thermodynamics, the definition of entropy, and mechanical equilibrium.

Moreover, the amount of calculation was enormous, and it was very easy to make a mistake during the integration.

For the first time since he’d started, Li Dong paused his pen.

’Is he stuck?’

Zheng Hua’s heart skipped a beat, but for some reason, seeing Li Dong stop actually made him breathe a sigh of relief.

This question involved entropy change, a topic from university-level thermodynamics. It was difficult for a high school student to understand the integration process. If Li Dong had solved it without a thought, Zheng Hua would have suspected he’d seen the problem before.

However, just as he was entertaining these doubts...

Li Dong suddenly smiled.

A smile that held a trace of... triumph?

’So that’s how it is...’

He thought to himself.

’Good thing I have a habit of lurking in the group chat, or this would have been a real pain.’

’Isn’t this just what Joule was talking about in the group the other day? The perfect combination of the mechanical equivalent of heat and a state function!’

’There’s no need to brute-force the calculation for that god-awful heating path!’

’Since it’s a state function, I just need to construct a mapping between the initial and final states!’

Li Dong picked up his pen and wrote a formula on his scratch paper:

dS = (dU + PdV) / T

He used the spring force equilibrium relationship, P = kx/A, combined with the ideal gas law to force a substitution for the temperature, T. The complex process that originally required path integration was, under his pen, instantly simplified into an algebraic sum of a few logarithmic terms.

Standing behind him, Zheng Hua stared at the unbelievably concise derivation on the scratch paper and felt like his mind was about to be blown.

He couldn’t help but let out a curse.

”Holy shit! You can do it like that?”

Only after he said it did he realize he had lost his composure.

At his outburst, all the spectating teachers turned to look at him in unison.

In their memory, Leader Zheng was always gentle and refined. Even with the most mischievous students, he would at most just frown.

But who would have thought that this typically composed teacher would publicly swear while watching a student solve a problem?

”Leader Zheng is... what’s wrong with him?” Teacher Xiaolin from the neighboring department asked in a hushed voice.

”I don’t know. Just how well is this student doing?”

Zheng Hua had no mind to pay attention to these whispers.

All his focus was on Li Dong’s scratch paper.

That concise line of reasoning was like a sledgehammer, violently striking at the foundations of his knowledge of physics.

Just then, Li Dong slowly wrote the final answer on his test paper:

ΔS = (2C_V + R) ln(x_final / x_initial)

Then he gently set down his pen, rubbed his slightly sore wrist, and let out a long breath.

”Teacher, I’m finished.”