EIT Electrical, Thermodynamics & Fluid Systems 5 — Questions and Answers
Question 1: In an op-amp inverting amplifier with R_f = 100 kΩ and R_in = 10 kΩ, the voltage gain is:
- −10 (Correct answer)
- +10
- −0.1
- +0.1
Correct answer: −10
Inverting amplifier gain A_v = −R_f / R_in = −100/10 = −10.
Question 2: The major head loss in a pipe system is primarily due to:
- Pipe wall friction over the pipe length (Correct answer)
- Pipe fittings and bends
- Entrance and exit effects
- Changes in elevation
Correct answer: Pipe wall friction over the pipe length
Major (Darcy-Weisbach) losses arise from friction along the straight length of the pipe; minor losses come from fittings.
Question 3: An isentropic process is one that is both:
- Reversible and adiabatic (Correct answer)
- Isothermal and adiabatic
- Reversible and isothermal
- Isobaric and reversible
Correct answer: Reversible and adiabatic
An isentropic (constant entropy) process requires both adiabatic (no heat transfer) and reversible conditions.
Question 4: A magnetic flux of 0.5 Wb through a 200-turn coil changes to zero in 0.1 s. The average induced EMF is:
- 1000 V (Correct answer)
- 100 V
- 10 V
- 500 V
Correct answer: 1000 V
EMF = −N ΔΦ/Δt = −200 × (0 − 0.5)/0.1 = 1000 V (magnitude).
Question 5: The specific speed of a pump is used to:
- Classify pump type and predict performance at varying scales (Correct answer)
- Determine the pump motor rating
- Calculate the pipe friction losses
- Size the pump impeller diameter only
Correct answer: Classify pump type and predict performance at varying scales
Specific speed N_s = N√Q / H^(3/4) classifies pumps (centrifugal, mixed, axial) and guides selection and scaling.
Question 6: The thermal efficiency of an ideal Otto cycle with a compression ratio r = 8 (γ = 1.4) is approximately:
- 56.5% (Correct answer)
- 40.0%
- 75.0%
- 30.0%
Correct answer: 56.5%
η_Otto = 1 − 1/r^(γ−1) = 1 − 1/8^0.4 ≈ 1 − 0.435 = 0.565 or 56.5%.
Question 7: For a Newtonian fluid, shear stress τ is related to the velocity gradient du/dy by:
- τ = μ (du/dy) (Correct answer)
- τ = ρ (du/dy)
- τ = μ (du/dy)²
- τ = ν (du/dy)
Correct answer: τ = μ (du/dy)
Newton's law of viscosity defines a Newtonian fluid: τ = μ du/dy, where μ is dynamic viscosity.
EIT Electrical, Thermodynamics & Fluid Systems 5
In an op-amp inverting amplifier with R_f = 100 kΩ and R_in = 10 kΩ, the voltage gain is: