Circuit Analysis & Thermodynamics Flashcards — Free Study Cards

Question

State the First Law of Thermodynamics for a closed system.

Answer

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

Question

State Kirchhoff's Current Law (KCL).

Answer

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

Question

State Kirchhoff's Voltage Law (KVL).

Answer

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

Question

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

Answer

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

Question

How do you deactivate sources when applying Superposition Theorem?

Answer

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

Question

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

Answer

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