EIT Electrical, Thermodynamics & Fluid Systems 3 — Questions and Answers
Question 1: Which law states that the algebraic sum of currents at any node in a circuit equals zero?
- Kirchhoff's Current Law (Correct answer)
- Kirchhoff's Voltage Law
- Ohm's Law
- Faraday's Law
Correct answer: Kirchhoff's Current Law
KCL (Kirchhoff's Current Law) is based on charge conservation: Σ I_in = Σ I_out at any node.
Question 2: The coefficient of performance (COP) of a Carnot refrigerator operating between T_H = 300 K and T_L = 250 K is:
- 5.0 (Correct answer)
- 0.2
- 4.0
- 1.2
Correct answer: 5.0
COP_Carnot,ref = T_L / (T_H − T_L) = 250 / (300 − 250) = 5.0.
Question 3: The hydraulic diameter of a rectangular duct with width 0.4 m and height 0.2 m is:
- 0.267 m (Correct answer)
- 0.3 m
- 0.4 m
- 0.2 m
Correct 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.
Question 4: An ideal transformer has 200 primary turns and 50 secondary turns. If the primary voltage is 120 V, what is the secondary voltage?
- 30 V (Correct answer)
- 480 V
- 60 V
- 15 V
Correct answer: 30 V
V_s/V_p = N_s/N_p → V_s = 120 × (50/200) = 30 V.
Question 5: For an ideal gas undergoing an isothermal process, which pair of quantities remains constant?
- Temperature and internal energy (Correct answer)
- Pressure and volume
- Enthalpy and entropy
- Pressure and temperature
Correct answer: Temperature and internal energy
For an ideal gas, internal energy depends only on temperature; if T is constant, so is u.
Question 6: The Reynolds number for flow of water (ν = 1×10⁻⁶ m²/s) at 2 m/s through a 50 mm diameter pipe is:
- 100,000 (Correct answer)
- 10,000
- 1,000,000
- 4,000
Correct answer: 100,000
Re = VD/ν = (2 × 0.05) / (1×10⁻⁶) = 100,000.
Question 7: In an RLC series circuit at resonance, the impedance is:
- Equal to the resistance R only (Correct answer)
- Zero
- Equal to the reactance XL
- Infinite
Correct answer: Equal to the resistance R only
At resonance, X_L = X_C, so the reactive parts cancel and Z = R.
EIT Electrical, Thermodynamics & Fluid Systems 3
Which law states that the algebraic sum of currents at any node in a circuit equals zero?