Making Steady Progress on the Road to Showing Off
"Before, I had no choice. Now, I just want to be a quiet, top student," Shen Qi said sincerely.
"Just keep showing off quietly, Shen Qi!" The boy wiped away his tears and stopped crying. A man should be self-reliant. He asked, "By the way, what was your score on the theory exam this time?"
280.
"I... I'm seriously unwell... I'm going to report you, Shen Qi!" The boy punched a nearby tree.
"Please don't do this, my friend." Shen Qi stood up and turned to leave.
"Wait a minute, boss!" The boy grabbed Shen Qi's arm and said eagerly, "Do you have a pen on you? The pen from yesterday's exam."
Shen Qi had a pen in his pocket, which Mu Rong had given him when he filled out the form, Mu Rong had forgotten to take it.
"Here, this is for you." Shen Qi took out a water-based pen and handed it to the boy.
"Thanks, sir!" The boy took Shen Qi's pen, his dejected expression vanishing. "With this magic pen in hand, exams are a breeze! Shen Qi, I wish you steady progress on your path of showing off, and that you'll soon become the new King of Show Offs showing off at Peking University!"
The CPhO experiment was underway the following day.
Experimental questions are worth 80 points, and theoretical questions are worth 280 points.
Experimentation plus theory equals the final score in this national final.
Shen Qi scored a perfect score of 280 in the theory exam the day before yesterday. As long as he doesn't make any silly mistakes in today's experimental section, his total score will be in a high range.
Why was that student from Hangzhou Second High School crying yesterday? Because he only got 172 points in the theory test. Even if he got a perfect score of 80 in the experiment, his total score could not be higher than Shen Qi's theoretical score.
The theoretical exam is undoubtedly the highlight of the national finals, but the experimental questions should not be neglected either.
All contestants were divided into two groups, one taking the exam in the morning and the other in the afternoon. The experimental questions for both the morning and afternoon sessions were electrical experiments, with some differences but similar difficulty.
Shen Qi was assigned to do the experimental questions in the afternoon.
The experimental instruments and equipment distributed by the invigilators are:
One DC Regulated Power Supply, two Digital Multimeter, two potentiometers, one Standard Resistance Box, one DC Galvanometer, one Constant Temperature Water Bath, one diode under test, one Programmable Calculator, and several Wires.
The experimental requirements are:
Design an experiment using the given experimental apparatus to accurately measure the forward Volt-Ampere Characteristic of a diode at t=27℃. The current range should be 0.5-1000μA, and at least 20 sets of data should be measured.
In addition, draw the circuit diagram, explain the experimental principle, write out the experimental steps, and design a table to record the experimental data. Also, draw the forward Volt-Ampere Characteristic curve of the diode and obtain the Reverse Saturation Current I0 and the Ideality Factor n.
If you have completed the steps described above and obtained the correct result, you are not finished yet. Please continue below:
When the current in the diode is constant, and the diode current is set to 5μA, 15μA, and 20μA, determine the relationship between voltage and temperature, derive the diode voltage Vg(0) at Absolute Zero, and analyze the characteristics of the diode Forward Junction Voltage at Absolute Zero under different constant current conditions and the reasons for its generation.
These are the requirements for the questions given on the experimental answer sheet.
This experimental question is not difficult, but it is not easy to get all 80 points. In addition to ensuring the accuracy of the steps and results written on the answer sheet, the contestant's practical actions are also counted in the scoring or deduction items.
Invigilators patrolled the laboratory, recording each contestant's practical actions. One-on-one supervision was impossible due to limited invigilators. Generally, one invigilator would monitor several contestants. Therefore, today's experimental session was divided into morning and afternoon sessions to separate the contestants.
Shen Qi had hands-on experience and practiced electrical experiments under Mu Rong's guidance.
The experimental question in the semi-finals was also about electricity, and it was the same in the finals.
Because electrical experimental instruments are simple and readily available, and experimental results can be verified on the spot, they are easy to set up as competition experiments.
Each contestant needs a Particle Accelerator, but the Chinese Physics Association doesn't have the capability or financial resources to organize one. The headquarters of the Chinese Physics Association only has one Particle Accelerator, and it's secondhand.
Shen Qi first used the Bridge Method to draw the measurement circuit diagram, and then set the temperature of the water bath to 27 degrees Celsius.
Connect the circuit according to the circuit diagram, adjust the initial value of the potentiometer to make the output voltage of the Voltage Divider Circuit 0, set the value of the resistance box to 10,000Ω, and zero the galvanometer.
After completing these basic experimental preparations, Shen Qi turned on the power and slowly adjusted the potentiometer to increase the ammeter reading.
Continue to adjust and repeatedly adjust the potentiometer and resistance box until the bridge is balanced at the set voltage value.
Then Shen Qi drew a record table on the answer sheet and recorded the data.
Voltage 0.430V, Current 0.52μA
Voltage 0.441V, Current 0.77μA
Shen Qi recorded 20 sets of data and plotted the forward Volt-Ampere Characteristic curve of the diode based on these data. He then calculated the Reverse Saturation Current I0 = 3.397 × 10^-14 A and the Ideality Factor n = 1.001.
The first part of this experiment is complete.
Up to this point, high school students need to master basic electrical experiment operations, as well as fundamental skills in data recording, processing, and calculation.
Therefore, the experimental section doesn't differentiate scores. Let alone physics competition contestants, even ordinary high school students with mediocre physics grades and passable hands-on skills can easily complete the first part of the national finals' experimental questions.
The second part is a little more complicated.
The diode voltage Vg(0) at Absolute Zero is derived, and the characteristics and causes of the diode Forward Junction Voltage at Absolute Zero under different constant current conditions are analyzed. This is actually a theoretical derivation and calculation problem.
The CPhO exam, in essence, tests theoretical knowledge.
Through theoretical derivation and calculation, Shen Qi obtained the values of Vg(0) as it approaches Absolute Zero as 1.225V, 1.233V, and 1.244V, which correspond to current values of 5μA, 10μA, and 15μA, respectively.
This concludes the experimental phase.
Many contestants, including Shen Qi, successfully completed the experiments and answered the questions.
The scores for the experimental questions were released on the same day.
No contestant achieved a perfect score of 80 on the experimental questions; the highest score was 79.5.
In the practical skills section, each contestant lost some points to varying degrees.
There's nothing we can do about it; there's no standard posture for actual practice, and no one can guarantee that every detail of their actions is perfect.
Shen Qi scored 77 points in the experiment, but lost 3 points. He can accept this result.
The experimental scores are out, which means the total score for this year's CPhO National Final is finalized.
The Chinese Physics Association has released the total score rankings for all contestants:
1. Shen Qi (Nangang Second High School), 357 points;
2. Tang Mengqi (Changjun High School), 352.5 points;
3. Su Xiaolie (Huazhong Normal University Affiliated High School), 352 points;
4. Lu Huaishong (Hangzhou Second High School), 350.5 points;
5. Ma Zixin (Yali High School), 349 points;
5. Han Xuance (Shijiacun Second High School), 349 points
7. Jin Shengqiang (Special Zone High School), 348.5 points;
200. Zeng Luna (Northeast Yucai School), 112 points.
The total scores are only published up to the top 200. The top 50 receive the National First Prize, those ranked 51-200 receive the national second prize, and those ranked 201-412 receive the third prize.
The national gold medal cutoff score has been set at 282 points, which is the score of the athlete ranked 50th.
The National Training Team's score was set at 298 points, which is the score of the player ranked 40th.
With the results finalized, 50 athletes won the National First Prize -class gold medal, and the top 40 gold medalists were selected for the National Training Team.
As in previous years, the top 50 contestants are mostly from top schools in physics and subject competitions in China.
Apart from Shen Qi, who ranked first.