NEET-XII-Physics
28: Heat Transfer
- #8A steel frame (K = 45 W m-1°C-1) of total length 60 cm and cross sectional area 0.20 cm2, forms three sides of a square. The free ends are maintained at 20°C and 40°C. Find the rate of heat flow through a cross section of the frame.Ans : Thermal conductivity, K = 45 W m-1 °C-1
Length, l = 60 cm = 0.6 m
Area of cross section, A = 0.2 cm2 = 0.2 × 10-4 m2
Initial temperature, T1 = 40°C
Final temperature, T2 = 20°C
`` \,\mathrm{\,Rate\,}\,\mathrm{\,of\,}\,\mathrm{\,flow\,}\,\mathrm{\,of\,}\,\mathrm{\,heat\,}=\frac{\,\mathrm{\,Temerature\,}\,\mathrm{\,difference\,}}{\,\mathrm{\,Thermal\,}\,\mathrm{\,resistance\,}}``
`` \frac{\,\mathrm{\,\Delta Q\,}}{\,\mathrm{\,\Delta \,}t}=\frac{kA({T}_{1}-{T}_{2})}{{\displaystyle l}}``
`` \frac{\,\mathrm{\,\Delta Q\,}}{\,\mathrm{\,\Delta \,}t}=\frac{45\times 0.2\times {10}^{-4}\left(40-20\right)}{0.6}``
`` =0.03\,\mathrm{\,W\,}``
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