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The rate of heat flow through the cross-section of the rod shown in figure is ($T_2 > T_1$ and thermal conductivity of the material of the rod is $K$)
  • A$\frac{{K\pi {r_1}{r_2}\left( {{T_2} - {T_1}} \right)}}{L}$
  • B$\frac{{K\pi {{\left( {{r_1} + {r_2}} \right)}^2}\left( {{T_2} - {T_1}} \right)}}{{4L}}$
  • C$\frac{{K\pi {{\left( {{r_1} + {r_2}} \right)}^2}\left( {{T_2} - {T_1}} \right)}}{{L}}$
  • D$\frac{{K\pi {{\left( {{r_1} + {r_2}} \right)}^2}\left( {{T_2} - {T_1}} \right)}}{{2L}}$
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