EIT Electrical, Thermodynamics & Fluid Systems 4 — Questions and Answers
Question 1: A pump adds 15 kW of power to water flowing at 0.05 m³/s. Assuming no losses, the pressure rise across the pump is approximately:
- 300 kPa (Correct answer)
- 150 kPa
- 750 kPa
- 30 kPa
Correct answer: 300 kPa
ΔP = W_pump / Q = 15000 / 0.05 = 300,000 Pa = 300 kPa.
Question 2: The Clausius inequality states that for any cyclic process:
- ∮ δQ/T ≤ 0 (Correct answer)
- ∮ δQ/T ≥ 0
- ∮ δQ/T = 1
- ∮ δQ = 0
Correct answer: ∮ δQ/T ≤ 0
The Clausius inequality ∮ δQ/T ≤ 0 holds for all real cycles, with equality only for reversible cycles.
Question 3: Which type of diode is specifically designed to operate in reverse breakdown for voltage regulation?
- Zener diode (Correct answer)
- Schottky diode
- LED
- Tunnel diode
Correct answer: Zener diode
Zener diodes maintain a nearly constant reverse voltage (the Zener voltage) when operated in controlled reverse breakdown.
Question 4: Water flows through a horizontal pipe that narrows from a 10 cm diameter to a 5 cm diameter. If the velocity in the larger section is 1 m/s, the velocity in the smaller section is:
- 4 m/s (Correct answer)
- 2 m/s
- 0.5 m/s
- 8 m/s
Correct answer: 4 m/s
By continuity, A₁V₁ = A₂V₂ → V₂ = V₁(D₁/D₂)² = 1×(10/5)² = 4 m/s.
Question 5: During a constant-volume (isochoric) heating process of an ideal gas, which of the following is true?
- All heat added goes to increasing internal energy (Correct answer)
- Work done by the gas equals heat added
- Entropy remains constant
- Enthalpy is unchanged
Correct answer: All heat added goes to increasing internal energy
At constant volume W = 0, so by the first law Q = ΔU; all heat increases internal energy.
Question 6: The power factor of a load with impedance Z = 6 + j8 Ω is:
- 0.6 lagging (Correct answer)
- 0.8 lagging
- 0.6 leading
- 1.0
Correct answer: 0.6 lagging
|Z| = √(36+64) = 10 Ω; PF = R/|Z| = 6/10 = 0.6; positive reactance → lagging.
Question 7: The enthalpy of vaporization (latent heat) of a substance at its normal boiling point represents:
- Energy required to convert liquid to vapor at constant pressure (Correct answer)
- Energy required to heat the liquid to boiling
- Energy released during condensation at constant volume
- Difference in internal energy between solid and liquid phases
Correct answer: Energy required to convert liquid to vapor at constant pressure
Enthalpy of vaporization h_fg = h_g − h_f is the heat absorbed per unit mass during phase change at constant pressure.
EIT Electrical, Thermodynamics & Fluid Systems 4
A pump adds 15 kW of power to water flowing at 0.05 m³/s.
Assuming no losses, the pressure rise across the pump is approximately: