---
The golden afternoon sunlight filtered through the glass window, spreading a warm glow across the classroom.
In the Class 12 'A' section's classroom, there was a light excitement in the air. A new teacher, Anirban Sir, had been taking classes for about a month now. Handsome, neatly dressed—there was a certain curiosity among the students. But more importantly, he explained things exceptionally well. The students often said, "Sir doesn't just teach, he makes us understand!"
Today's topic — Capacitor and Capacitance.
As soon as Sir entered the class, he smiled,
"How is everyone doing?"
"Yes, Sir!"
After taking attendance, he sweetly said,
"Alright then, let's start a new chapter today. It's called Capacitor and Capacitance. But before the explanation, let me tell you a story."
Everyone's eyes sparkled with interest.
He laughed and said, "What do you do if your phone runs out of charge?"
One girl giggled and said, "Sir, I take out the power bank!"
"That's right," Sir smiled. "What you call a power bank, in physics, is a kind of capacitor. The only difference is — the power bank stores chemical energy, but a capacitor stores electrical energy."
The students listened attentively. Sir placed one or two metal plates on the table and said,
"Imagine these are two metal plates. There is air or some other insulating material between them. If I give a positive charge to one plate and a negative charge to the other…"
He drew charge symbols carefully on the board with chalk.
"…then an electric field will form between the plates, maintaining a certain potential difference. This system is called a capacitor."
A student asked, "Sir, does a capacitor always hold a charge?"
"Good question," Sir replied. "A capacitor does not generate charge by itself, but it can store charge. Like your diary—if you don't write anything, it's empty. But if you write, it keeps memories. A capacitor works the same way — it stores your charge."
Another asked, "Sir, then what is capacitance?"
"Capacitance is the ability of a capacitor to store a certain amount of charge at a given potential difference. Its unit is the Farad. But in reality, we use smaller units like microfarads (μF) or picofarads (pF)."
The students wrote down notes, trying to understand.
"Let me give you an example," Sir said. "If you bring two plates closer, the attraction between them increases, and the electric field becomes stronger. Then, the capacitance also increases. Similarly, the size of the plates, the distance between them, and the dielectric material all affect the capacitance."
A girl laughed and said, "Sir, this topic used to be so boring, but you explained it so simply!"
"Thank you," Sir smiled. "Physics isn't something separate from life. Learn to feel it, then understanding becomes easy."
Taking chalk in hand, Sir said at the board,
"Now we will learn how multiple capacitors work together. Just like multiple friends working together — sometimes it makes things easier, sometimes harder."
He paused, looked around the class, and smiled—
"Imagine you have two friends, each capable of holding different things. But how they work can be different — sometimes side by side, sometimes one behind the other. This is just like the connection of capacitors!"
---
---
He wrote in large letters on the board:
Series Combination:
\frac{1}{C} = \frac{1}{C_1} + \frac{1}{C_2} + \frac{1}{C_3} + \dots
"When capacitors are connected one after another in a line—like students standing in a queue—they are said to be in series. Do you know what happens then?"
The students nodded.
"The potential difference divides across each capacitor, but the charge on all remains the same. As a result, the total capacitance decreases. It's like having three friends, but when they work together, it takes more time."
Then he wrote on the board:
Parallel Combination:
C = C_1 + C_2 + C_3 + \dots
"And when capacitors are placed side by side, like friends sitting together, they are in parallel. In this case, each capacitor experiences the same voltage, but the charge divides among them. And the result? The total capacitance increases! They can hold a lot more together."
A girl smiled broadly and said, "Sir, then if I get to choose in the final exam, I'll definitely pick parallel!"
Everyone laughed. Sir smiled and said, "But make sure you see what the question asks. Series connection is needed in many places too, like timing circuits."
Then Sir wrote:
Energy Stored in a Capacitor:
U = \frac{1}{2} CV^2
"You must be wondering, the capacitor stores charge, yes, but where does the energy get stored? Remember this formula—when a capacitor is charged, it stores some potential energy. Just like you store your secrets in your diary. Inside itself, there is some voltage along with the charge."
Then he said—
"Just like we accumulate fatigue at the end of the day, a capacitor stores energy and can release it when needed. In many electronic circuits, a capacitor acts as a temporary energy source. It's like the light stays on for a moment even if the power goes out."
One student exclaimed, "Sir, your way of explaining is like telling a story!"
Sir laughed, "Physics is a story. If you can feel it, you don't need to force it into your head."
The period ended. The students felt sad—the class had ended so beautifully.
But there was joy in understanding. Some notebooks were full, some minds had made space for capacitors, capacitance, and the smiling explanations of Sir.
---
Before Sir left, Bosundhara stood up. Seeing her stand, Sir became a bit alert.
"Yes, Bosundhara, speak."
Bosundhara said,
"Sir, I haven't been able to attend class for a few days. I had some family issues. Could you please explain the chapter on electric potential in the electric field to me?"
Sir said, "There is a revision class on Thursday during the eighth period. Come then, I'll explain it."
Then Bosundhara said, "Sir, I won't be able to come that day. My mother is sick at home. I have to take her to a doctor in Kolkata. And I'm really struggling to understand the chapter. Please explain it a little now. You know how these chapters connect with each other. If you miss the beginning, you can't understand anything later. My batch's teacher will take the exam. If I don't understand the electric potential chapter, I won't be able to do anything. My father said if I don't perform well in the batch, he will stop my studies. Please help me, Sir. Please."
Hearing Bosundhara's plea, Anirban Sir's heart melted.
Actually, hearing about family pressure made him a little emotional because he had been an orphan since childhood.
Anirban Sir asked, "Alright, tell me what you want. What can I do for you?"
Bosundhara said, "Sir, can I come to your cabin during the tiffin period today? You can personally explain it to me there."
Anirban Sir said, "Okay, fine. Come."
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To be continued...
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