Concept Notes (Deep Explanation + Examples)
A capacitor is an electrical component that stores energy in the form of an electric field. It consists of two parallel plates separated by an insulating material (dielectric).
The ability of a capacitor to store charge is called capacitance (C) and is measured in farads (F).
🔹 Basic Formula
Where:
- CCC = Capacitance
- QQQ = Charge stored
- VVV = Potential difference
🔸 1. Capacitors in Series
When capacitors are connected one after another, the total charge (Q) on each capacitor is same, but voltage divides.
🧠 Formula:
📘 Example:
If three capacitors of 6 μF, 3 μF, and 2 μF are connected in series, then
Hence, 
.
🔹 Voltage Division:
The capacitor with smaller capacitance has higher voltage across it.
💡 Real-life analogy: Think of water passing through narrow pipes in sequence — the flow (charge) is same, but pressure drop (voltage) varies.
🔸 2. Capacitors in Parallel
When capacitors are connected side by side, each has the same voltage, but charge divides.
🧠 Formula:
📘 Example:
If 2 μF, 3 μF, and 5 μF capacitors are connected in parallel,
.
🔹 Charge Division:
Since voltage is same, each capacitor stores charge according to its capacitance.
💡 Real-life analogy: Like multiple tanks connected to the same water source — all fill together and store more total water.
🔹 Energy Stored in a Capacitor
🧠 Example:
For a 5 μF capacitor charged to 10 V,
🔹 Combination of Series and Parallel
In complex circuits, capacitors may be mixed in both series and parallel.
To solve:
- Simplify step-by-step (series → equivalent → parallel → equivalent)
- Use correct formula for each stage
- Apply
to find charge or voltage.
🔹 Diagram (Explain in Words)
🧩 Imagine:
- Series connection: Capacitors connected end-to-end, like small rectangles linked in a line, with same charge flowing through each.
- Parallel connection: Capacitors placed side-by-side, all connected to same two points, sharing the same voltage.
🔹 ECET Exam Tip
Capacitor combination problems are very frequent in ECET Physics section.
Expect 2–3 marks questions involving equivalent capacitance or energy stored.
Always check units (μF → F) carefully.
⚙️ Formulas
🔟 10 MCQs (ECET + GATE Hybrid)
- Three capacitors 2 μF, 3 μF, and 6 μF are connected in series. The equivalent capacitance is:
A) 1 μF
B) 2 μF
C) 3 μF
D) 4 μF - For capacitors in parallel, the total capacitance is:
A) Product/Sum
B) Sum of reciprocals
C) Sum of capacitances
D) None - A 4 μF capacitor is charged to 10 V. The energy stored is:
A) 0.2 J
B) 0.0002 J
C) 0.0004 J
D) 0.4 J - In a series combination, which remains constant across all capacitors?
A) Voltage
B) Charge
C) Capacitance
D) Energy - In a parallel combination, which remains constant?
A) Charge
B) Voltage
C) Energy
D) None - If
and 
are connected in parallel, then 
is:
A) 9 μF
B) 2 μF
C) 4.5 μF
D) 3 μF - The unit of capacitance is:
A) Ohm
B) Henry
C) Farad
D) Coulomb - Two capacitors each of 10 μF are connected in series across 100 V. Voltage across each capacitor is:
A) 25 V
B) 50 V
C) 75 V
D) 100 V - A capacitor stores energy due to:
A) Magnetic field
B) Electric field
C) Resistance
D) Current - Equivalent capacitance of three 6 μF capacitors in parallel is:
A) 6 μF
B) 12 μF
C) 18 μF
D) 3 μF
✅ Answer Key
Q No | Answer
1 | A
2 | C
3 | B
4 | B
5 | B
6 | A
7 | C
8 | B
9 | B
10 | C
🧠 MCQ Explanations
1️⃣ In series: 
, so 
.
2️⃣ In parallel, capacitances add directly — hence option C.
3️⃣ 
.
4️⃣ In series, same charge flows through all capacitors.
5️⃣ In parallel, same voltage appears across all capacitors.
6️⃣ 
.
7️⃣ SI unit of capacitance is Farad.
8️⃣ Two equal capacitors in series share equal voltage — 
.
9️⃣ Capacitor stores energy in electric field.
10️⃣ In parallel: 
.
🎯 Motivation (ECET 2026 Specific)
Capacitors in series and parallel appear almost every year in ECET due to their conceptual + numerical mix.
These questions check your clarity on basics and unit conversion accuracy.
Practicing them builds your problem-solving speed in Physics numericals — a rank booster for ECET 2026 aspirants. ⚡
Stay consistent — one topic daily keeps you ahead of 90% of students!
📲 CTA
Join our ECET 2026 CSE WhatsApp Group for daily quizzes & study notes:
👉 https://chat.whatsapp.com/GniYuv3CYVDKjPWEN086X9
