Switching and Capacitor Network Redistribution
Ideal capacitor switching is treated by initial and final electrostatic states, with battery voltages, isolated-node charge conservation, and Q=C Delta V applied to each topology.
Why this shows up in the exam
multi-switch capacitor circuits · charge through a switch · long-time plate charge after reconnection
Learn the idea
Switch operations change network constraints; analyze each steady state separately. A switch can isolate a charged node, connect new equipotential nodes, or let charge redistribute. Charge conserved before closure may move after closure, but isolated-node totals remain constrained.
🧠 Memory hook: Redraw before and after; never mix the two topologies.
Get this one clearly and it pays off every single time it shows up in the paper. 🎯
Formulas & facts to keep ready
- Q_i = C_i(V_a-V_b) — signed plate charge in each topology
- sum Q_isolated node = constant — across switching when node has no conducting path to source
How to approach it
- 1Draw the initial steady state
- 2Record conserved isolated-node charges
- 3Redraw final state and solve node potentials
Common slip-ups that cost marks
- •Keeping an obsolete series or parallel relation after switching
- •Conserving charge on a node connected to a battery
- •Ignoring initial capacitor charge
🌟 That's the whole idea — you've got this. Try the practice set below; every question you attempt makes it stick a little harder.
Original chapter practice
Original questions for this chapter, not past-paper questions or an exact mapping to this individual concept.
Two point charges 1 microC and 2 microC are 1 m apart in vacuum. Take k = 9 x 10^9 SI. Find the force magnitude.
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