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Question #43912

Difficulty: 8/10 | 🟢 Free

The Question

A bimetallic cantilever strip of length LL and uniform flexural rigidity EIEI is heated such that the temperature difference between its top and bottom surfaces is ΔT(x)=ΔT0(xL)\Delta T(x) = \Delta T_0 \left(\frac{x}{L}\right), where xx is the distance from the fixed end (x=0x=0). This temperature difference induces a local curvature d2ydx2=βΔT(x)\frac{d^2y}{dx^2} = \beta \Delta T(x), where β\beta is a constant depending on the material properties. The effective spring constant keffk_{eff} of the strip at its free end is defined by equating the total elastic strain energy stored in the strip to the potential energy of an equivalent spring 12keffymax2\frac{1}{2}k_{eff}y_{max}^2, where ymaxy_{max} is the transverse deflection at the free end. Assuming small deflections, what is the value of keffk_{eff}?

Options

  • A.

    3EIL3\frac{3 EI}{L^3}

  • B.

    4EIL3\frac{4 EI}{L^3}

  • C.

    8EIL3\frac{8 EI}{L^3}

  • D.

    12EIL3\frac{12 EI}{L^3}

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How the Examiner Thinks

Multi-Concept_Bridge

Master problems that require linking physics and math concepts to solve complex competitive questions.

Concepts Behind This Question

Bimetallic Strip Curvature|Effective Spring Constant|Integration

Why This Question Is Tricky

Common Mistakes

Students often memorize the effective spring constant of a cantilever beam as k=3EI/L3k = 3EI/L^3.

However, this standard value is specifically derived for a point load applied at the free end, which produces a linear bending moment profile M(x)=P(L−x)M(x) = P(L-x).

In this thermal problem, the non-uniform temperature gradient creates a fundamentally different curvature profile κ(x)∝x\kappa(x) \propto x.

The effective spring constant, defined via energy equivalence, depends strictly on the mode shape of the deflection.

By blindly applying the standard mechanical formula, students fail to account for the altered strain energy distribution and deflection shape caused by the distributed thermal moment, leading to an incorrect spring constant.

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Question Information

SubjectPhysics
ChapterThermal Properties of Matter - Class 11 Part 2
ConceptBimetallic Strip Curvature
Difficulty8
Cognitive Load7
Target Solve Time160 sec
AccessFree