Two wires of resistance $R_1$ and $R_2$ have temperature coefficient of resistance ${\alpha _1\,}{\rm{ and \,}}{\alpha _2}$, respectively. 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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