Home › Board exam reviewer › Engineering materials

Engineering materials: board exam questions with solutions

On the ECE exam under General Engineering and Applied Sciences (GEAS) and the REE exam under Engineering Sciences and Allied Subjects (ESAS). Try each question before you open its solution.

Loading the reviewer… (it needs JavaScript)

Questions

1. At room temperature, which metal has the highest electrical conductivity?

  1. Copper
  2. Silver
  3. Gold
  4. Aluminum
Show the answer and solution

Answer: B. Silver

Silver's resistivity is about 1.59×10⁻⁸ Ω·m, slightly below copper's 1.68–1.72×10⁻⁸ Ω·m.

2. Pure silicon doped with phosphorus becomes:

  1. An n-type semiconductor
  2. A p-type semiconductor
  3. An insulator
  4. An intrinsic semiconductor
Show the answer and solution

Answer: A. An n-type semiconductor

Phosphorus is a group V donor. Its fifth valence electron becomes a free carrier, which makes the silicon n-type.

3. Find the resistance of 100 m of copper wire with a 2.5 mm² cross-section. (ρ = 1.72×10⁻⁸ Ω·m)

  1. 0.688 Ω
  2. 6.88 Ω
  3. 0.0688 Ω
  4. 0.172 Ω
Show the answer and solution

Answer: A. 0.688 Ω

R = ρL/A = 1.72×10⁻⁸ × 100/(2.5×10⁻⁶) = 0.688 Ω.

4. A copper winding measures 10 Ω at 20 °C. What is its resistance at 75 °C? (α₂₀ = 0.00393/°C)

  1. 12.95 Ω
  2. 10.22 Ω
  3. 12.16 Ω
  4. 7.84 Ω
Show the answer and solution

Answer: C. 12.16 Ω

R = R₂₀[1 + α(T − 20)] = 10[1 + 0.00393 × 55] = 12.16 Ω.

5. Which material is usually laminated into power transformer cores for high permeability and low hysteresis loss?

  1. Copper
  2. Aluminum
  3. Brass
  4. Silicon steel
Show the answer and solution

Answer: D. Silicon steel

Silicon (electrical) steel has a narrow hysteresis loop and higher resistivity, which reduces hysteresis and eddy-current losses. Copper, aluminum and brass are not ferromagnetic.

6. How many atoms belong to one face-centered cubic (FCC) unit cell?

  1. 2
  2. 4
  3. 8
  4. 14
Show the answer and solution

Answer: B. 4

8 corners × 1/8 + 6 faces × 1/2 = 1 + 3 = 4. BCC has 2.

7. Which pair of properties defines a superconductor below its critical temperature?

  1. Zero resistance and very high permeability
  2. Very high resistance and zero permeability
  3. Zero thermal conductivity and zero resistance
  4. Zero DC resistance and expulsion of magnetic flux
Show the answer and solution

Answer: D. Zero DC resistance and expulsion of magnetic flux

Below T_c, a superconductor has zero DC resistance and expels magnetic fields from its interior (the Meissner effect).

8. An aluminum conductor replaces a copper one of the same length and resistance. Approximately what fraction of the copper conductor's mass does it have? (ρ_Al = 2.82×10⁻⁸ Ω·m, ρ_Cu = 1.72×10⁻⁸ Ω·m, densities 2.70 and 8.96 g/cm³)

  1. 1.64
  2. 0.30
  3. 0.49
  4. 0.61
Show the answer and solution

Answer: C. 0.49

Same R and L means A_Al/A_Cu = ρ_Al/ρ_Cu = 1.64. Mass ratio = 1.64 × 2.70/8.96 = 0.49, so it is roughly half the weight despite the larger cross-section.

Other topics in the same subjects

Physics: mechanics · Physics: waves, electricity and magnetism · General chemistry · Thermodynamics · Engineering economics · Engineering management · Computer fundamentals and programming · RA 9292 and ethics (electronics) · Fluid mechanics · Strength of materials · RA 7920 and ethics (electrical) · PEC Part 1: general requirements

An independent, free reviewer: not affiliated with the PRC or the Boards. Subject weights and passing rules are from the PRC examination programs and the laws (RA 9292, RA 7920); check the current PRC program before you file. Code questions follow the Philippine Electrical Code 2017 Part 1; check them against your own copy of the Code.