My IQ has been increasing year by year.

Chapter 65 Intuition

Two o'clock in the afternoon.

The First Physics Laboratory at the High School Affiliated to National Taiwan Normal University.

This is a very simple, even somewhat old-fashioned, electrical laboratory.

The window was half open.

The air was filled with the distinctive smell of pine resin, a mixture of soldering iron and old bakelite.

Six large wooden experimental tables.

The tools that had been prepared beforehand were laid out.

A bulky, black MF47 analog multimeter.

There is a thin layer of scratches on the plastic case of the watch face.

Two wires with alligator clips, one red and one black.

A standard 1.5V No. 1 dry cell battery with its outer casing wrapped in insulating tape.

Right in the middle of these tools.

There was a square box, tightly sealed with black engineering plastic.

(Black box model, a very classic type of physics competition problem, patch)

The box is about the size of a palm.

There were no seams on any side; it was completely sealed with super glue.

The top of the box.

Four brass terminals were exposed.

The letter A, B, C, and D are engraved on it.

Professor Wang pulled up a wooden chair with peeling paint.

I sat at the very front of the laboratory.

He was holding that enamel tea mug in his hand.

He was like a kind but cunning old man watching his grandchildren play in the mud.

"morning."

Professor Wang took a sip of tea and spoke with a smile.

"Those messy equivalent circuits, diodes, stuffed into your brains."

"Now."

He gestured with his chin towards the black boxes on the lab benches.

"It's all in this box."

"In this box, there are wires and resistors with different resistance values."

"There is also a diode that conducts electricity in one direction."

Professor Wang placed the teacup on the bar stool next to him.

"The rules are very simple."

"Unauthorized opening of the box is absolutely prohibited."

"You can only use the multimeter and batteries on your desk."

"Half an hour."

"Draw the actual circuit diagram inside the box accurately on paper for me."

"Which terminal is connected to the resistor, which terminal is connected to the positive terminal of the diode, and which terminal is connected to the negative terminal."

Mark it clearly.

Professor Wang leaned back in his chair.

"start."

With a command given.

In the laboratory.

The crisp click sound of the multimeter's range selector knob turning was heard instantly.

Wang Huashao grabbed the two probes of the multimeter.

I turned the gear to the ohm setting.

He took a deep breath.

I tried to force my still-dizzy brain to start.

"It's just measuring resistance, right? Four terminals, measure two at a time, and find the pattern."

He muttered something to himself to bolster his courage.

The red alligator clip of the marker bit into the A-pillar.

The alligator clip on the black watch pen snapped into the B-pillar.

The multimeter pointer deflected rapidly and stopped at a middle mark.

"About 50 ohms."

Wang, who spoke little, quickly jotted down on the paper: AB = 50.

Then, he kept the red pen on A.

The black probe was moved to the C-pillar.

The pointer moved slightly and stopped at an extremely large value.

"The resistance between AC is very high—are they connected in series?"

Wang talks little, but the tests go faster the more he does.

A and D, B and C, C and D.

He finished one round of testing in less than three minutes.

Looking at the six messy data points jotted down on the draft paper.

He tried to piece together a hybrid circuit diagram with diodes in his mind using these six data points.

but.

I can't spell it out.

He discovered that no matter how he drew the diagram according to these six resistance values, there would be contradictions.

Because the box contains not only ordinary resistors, but also diodes with different forward and reverse resistances, and even parallel branches of resistors and diodes.

"That's not right—"

Wang, who spoke little, scratched his head, making his short hair look like a bird's nest.

He picked up the test leads, ready to remeasure the resistance between A and B.

This time, he casually clipped the black pen onto A.

The red marker was clipped onto B.

(This is completely reversed from the positive and negative poles measured in the first measurement.)

The multimeter pointer suddenly veered off course.

It hit the far right.

The resistance is almost zero!

Wang, who spoke little, widened his eyes instantly.

He stared intently at the pointer of the multimeter.

Mouth slightly open.

What happened?

The resistance between A and B was 50 ohms just now, but after changing the position of the test probe, it became zero?

He suddenly realized what was happening.

"A diode!"

As we just discussed this morning, forward conduction is enabled, and reverse conduction is disabled!

This realization did not make him feel at ease.

Instead, it plunged him into even greater despair.

Because the six data points he just recorded didn't even consider the positive and negative terminals; they were all randomly generated with his eyes closed.

How many of them are equivalent resistances for diode forward conduction?

How many of them are infinity when the reverse cutoff occurs?

Everything is in chaos.

"Brother Kai————"

Wang Huashao turned his head, looked at Zhou Kai on the lab table next to him, and let out a wail.

"Is this box leaking electricity?"

"What were the values of A and C I just measured? My mind is completely filled with that resistor cube from this morning spinning around!"

"Why are these stats so unpredictable and constantly changing?!"

Zhou Kai wasn't much better than him.

He was also rubbing his throbbing temples.

Zhou Kai attempted to use several algebraic equations to deduce the topological structure inside the box.

However, he discovered that due to the nonlinearity of the diode, the coefficients of the equation were not fixed.

This is not a problem that mathematics can solve.

"Don't panic."

Zhou Kai smiled wryly, holding the wire in his hand and testing it.

"There must be a branch circuit that has been short-circuited by the diode."

"Try it slowly, and be sure to remember the positive and negative terminals."

Throughout the laboratory.

It descended into a chaotic trial.

The sound of alligator clips hitting the terminals was accompanied by the boys' frustrated sighs.

Human short-term memory is affected by such multivariable and irregular information feedback.

Especially when the brain is extremely fatigued.

The system was immediately declared down.

In front of the first experimental table.

Lin Yi dragged a chair over.

Unlike the boys, she didn't blindly poke around while sweating profusely.

She rested her chin on her hand, and with the other, she tapped the tabletop idly with the red pen.

The intense theoretical classes in the morning did make her feel a little sleepy.

She stared at the black square box in front of her for a long time.

Then, he reached up and rubbed his eyes.

"trouble."

She muttered something.

I pulled the chair forward a little and sat up a bit straighter.

Lin Yi picked up the two probes of the multimeter.

She didn't test all the combinations.

She glanced at the black square box.

There must be a main road and several branches at the four endpoints.

The diode is hidden inside.

She turned the multimeter to the DC voltage setting.

Use that 1.5V dry cell battery as an external power source.

The red marker is placed on A, and the black marker is placed on C.

The pointer deflected slightly.

There is a weak voltage.

then.

Her fingers nimbly twirled.

The red and black markers flipped over on my fingertips.

Connect black to A, and red to C.

The pointer is still deflecting.

but.

Lin Yi's eyes narrowed slightly.

The degree of deflection is different from before.

There is a slight difference, almost imperceptible to the naked eye.

Most people would assume this is normal error of the multimeter or unstable battery voltage.

But Lin Yi is different.

Her intuition told him.

This is not an error.

This is unique to diodes, characterized by a slight on-state voltage drop.

"Between A and C, the positive electrode is at C."

Lin Yi made a firm conclusion in his mind.

She immediately switched the multimeter back to the ohm setting.

The test was conducted twice, between A and C.

The existence of the voltage drop was verified, and the forward and reverse resistance values of the branch containing the diode were also determined.

then.

She placed the pen on B and D.

The pointer remained stationary.

Reversal.

It remained motionless.

"BD means no-load circuit break."

It only took less than four touches.

Lin threw the pen on the table.

He pulled out the black ballpoint pen from the canvas bag that had been washed until it was somewhat faded.

Remove the pen cap.

On the draft paper.

A hybrid series-parallel circuit diagram with diodes was quickly drawn.