Two rods of same area of cross-section have lengths $L$ and $2 \,L$ and coefficients of linear expansion $2 \alpha$ and $\alpha$ respectively. If they are welded to form a composite rod of length $3 \,L$, then the coefficient of linear expansion of the composite rod is

  • A
    $\frac{3 \alpha}{2}$
  • B
    $3 \alpha$
  • C
    $\frac{3 \alpha}{4}$
  • D
    $\frac{4 \alpha}{3}$

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