Two wires of resistances $R_1$ and $R_2$ have temperature coefficients of resistance $\alpha_1$ and $\alpha_2$ respectively. If these are joined in series,the effective temperature coefficient of resistance is:

  • A
    $\frac{\alpha_1 + \alpha_2}{2}$
  • B
    $\sqrt{\alpha_1 \alpha_2}$
  • C
    $\frac{\alpha_1 R_1 + \alpha_2 R_2}{R_1 + R_2}$
  • D
    $\frac{\sqrt{R_1 R_2 \alpha_1 \alpha_2}}{\sqrt{R_1^2 + R_2^2}}$

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