If a composite bar of steel and copper is heated, the copper bar will be under:
Try it first: pick an option, then read the explanation.
Correct answer: D. None of these
Asked in SSC JE 22/01/2018 (Morning)
Detailed Explanation
Copper has a higher coefficient of thermal expansion (≈ 17 × 10⁻⁶ /°C) than steel (≈ 12 × 10⁻⁶ /°C).
Why “None of these” Is Correct
On heating, copper wants to expand more but is restrained by the steel, so copper is in compression and steel in tension. Compression is not among (a)–(c), so the answer is (d) None of these.
| Situation | Stress |
|---|---|
| Bar fully restrained, temperature change ΔT | σ = EαΔT (compressive on heating, tensile on cooling) |
| Composite bar heated (ends held together) | Material with higher α → compression; lower α → tension |
| Composite bar cooled | Higher α → tension; lower α → compression |
Why the Other Options Are Wrong
- A. Tension: Tension is in the steel (lower α), not the copper.
- B. Shear: Thermal restraint here causes direct stress, not shear.
- C. Torsion: There is no twisting in a heated composite bar.
Key Point
Heated composite bar: higher-α material (copper) in compression.
Key Concepts for Students
- On cooling, copper would be in tension.
- Force in copper = force in steel (equilibrium).
- αs·ΔT + σs/Es = αc·ΔT − σc/Ec (compatibility).
Practice more: this is question 41 in Stress and Strain MCQs – Part 3. Try the whole set and check every answer instantly.