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Foundation6 past questions

Capacitors, capacitance, and combinations

Learn about parallel plate capacitors, series and parallel combinations, and how capacitance changes with geometry and dielectrics.

Why this shows up in the exam

You will solve NEET questions on calculating equivalent capacitance and understanding capacitor behavior in circuits.

How NEET tests this

Numerical · 5 QsStatement analysis · 2 QsDirect recall

Learn the idea

Capacitance depends on geometry (C = ε₀εᵣA/d) and adds when plates are placed side‑by‑side (parallel) but reduces when plates are stacked end‑to‑end (series). In a series of identical caps the safe voltage adds because each shares the total voltage equally.

🧠 Memory hook: Parallel plates are like lanes on a highway – more lanes (parallel) give more traffic (capacitance). Series plates are like a single narrow lane stretched out – traffic slows (capacitance drops) but the road can hold a higher total speed limit (voltage adds).

Get this one clearly and it pays off every single time it shows up in the paper. 🎯

Formulas & facts to keep ready

  • C = ε₀εᵣA/d for a parallel‑plate capacitor
  • For n capacitors in parallel: C_eq = ΣC_i
  • For n capacitors in series: 1/C_eq = Σ1/C_i
  • In series identical caps: C_eq = C/n
  • Breakdown voltage of series identical caps: V_total = n × V_individual
  • C varies directly with plate area and inversely with plate separation

How to approach it

  1. 1Identify whether the given capacitors are in series or parallel
  2. 2Write the appropriate formula for C_eq (sum for parallel, reciprocal sum for series)
  3. 3If geometry changes, apply C ∝ A/d to find the new value
  4. 4For breakdown voltage in series, multiply the individual rating by the number of identical caps

Worked example — watch it click

Three capacitors, each of capacitance C and of breakdown voltage V, are joined in series. The capacitance and breakdown voltage of the combination will be:

  • A)3C, V/3
  • ✅C/3, 3V
  • C)3C, 3V
  • D)C/3, V/3

The concept behind this problem

The example checks that you apply the series rule for both capacitance (C/3) and the fact that the safe voltage of identical series caps adds up to 3V.

Step by step

  1. 1For capacitors in series: C_eq = C/n = C/3.
  2. 2For breakdown voltage in series, the voltage divides equally across identical capacitors.
  3. 3Each can withstand V, so the combination can withstand n×V = 3V before any single capacitor breaks down.

Watch out

Thinking the series combination can still survive only V instead of the multiplied 3V.

Common slip-ups that cost marks

  • •Adding capacitances in series as if they were in parallel
  • •Assuming the breakdown voltage of a series string stays the same as a single capacitor
  • •Ignoring that voltage divides equally only when the capacitors are identical

🌟 That's the whole idea — you've got this. Try the practice set below; every question you attempt makes it stick a little harder.

Practise it

These are real questions from past NEET papers that test this exact idea.

Question 1 of 6NEET 2009

Three capacitors, each of capacitance C and of breakdown voltage V, are joined in series. The capacitance and breakdown voltage of the combination will be:

Push further

More challenging

14 harder questions built from the past papers above — a step up in difficulty, with distractors designed so you can't get there by elimination. Written and checked by our reviewers, not from a real paper.

Question 1 of 14

A circuit consists of two capacitors, C1 = 4 microfarads and C2 = 8 microfarads, connected in series. This combination is then connected in parallel with a third capacitor C3 = 6 microfarads. What is the total equivalent capacitance of the circuit?

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