Electrical, Thermodynamics & Fluid Systems Flashcards

Which law states that the algebraic sum of currents at any node in a circuit equals zero?

Answer: Kirchhoff's Current Law

KCL (Kirchhoff's Current Law) is based on charge conservation: Σ I_in = Σ I_out at any node.

The coefficient of performance (COP) of a Carnot refrigerator operating between T_H = 300 K and T_L = 250 K is:

Answer: 5.0

COP_Carnot,ref = T_L / (T_H − T_L) = 250 / (300 − 250) = 5.0.

The hydraulic diameter of a rectangular duct with width 0.4 m and height 0.2 m is:

Answer: 0.267 m

D_h = 4A/P = 4(0.4×0.2) / [2(0.4+0.2)] = 0.32/1.2 ≈ 0.267 m.

An ideal transformer has 200 primary turns and 50 secondary turns. If the primary voltage is 120 V, what is the secondary voltage?

Answer: 30 V

V_s/V_p = N_s/N_p → V_s = 120 × (50/200) = 30 V.

For an ideal gas undergoing an isothermal process, which pair of quantities remains constant?

Answer: Temperature and internal energy

For an ideal gas, internal energy depends only on temperature; if T is constant, so is u.

The Reynolds number for flow of water (ν = 1×10⁻⁶ m²/s) at 2 m/s through a 50 mm diameter pipe is:

Answer: 100,000

Re = VD/ν = (2 × 0.05) / (1×10⁻⁶) = 100,000.

In an RLC series circuit at resonance, the impedance is:

Answer: Equal to the resistance R only

At resonance, X_L = X_C, so the reactive parts cancel and Z = R.