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Circuit Analysis & Thermodynamics

Public Notes

Flashcards(6)

First Law

State the First Law of Thermodynamics for a closed system.

Q − W = ΔU. Heat added to the system minus work done by the system equals the change in internal energy.

KCL

State Kirchhoff's Current Law (KCL).

The algebraic sum of all currents at any node is zero — currents entering equal currents leaving. Charge cannot accumulate at a node.

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KVL

State Kirchhoff's Voltage Law (KVL).

The algebraic sum of all voltages around any closed loop is zero — voltage rises equal voltage drops (energy conservation).

Second Law

A Carnot engine operates between 800 K and 400 K. What is its efficiency?

η = 1 − T_cold/T_hot = 1 − 400/800 = 0.5 = 50%. This is the theoretical maximum — no real engine can exceed it.

Superposition

How do you deactivate sources when applying Superposition Theorem?

Voltage sources → replace with short circuit (0Ω wire). Current sources → replace with open circuit (remove the branch).

Why can't Superposition be applied directly to power calculations?

Power is nonlinear (P = I²R or V²/R). You must find total current/voltage first using superposition, then calculate power from the total.