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Explain thermal resistance. |
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Answer» Solution :In thermal steady state, heat current in a rod in thermal steady state, `H=(Q)/(t)=kA[(T_(1)-T_(2))/(L)]=([T_(1)-T_(2)])/(((L)/(kA)))` Comparing the above EQUATION with that of electric current `I=(V)/(R)=(V_(1)-V_(2))/(R)`is obtained from Ohm.s law. We can say that as we get electric current by applying potential difference, similarly we can have heat current between TWO ends we have heat current between two ends of conducting substance by establishing temperature difference. By analogy we can say that as the property of sucstance to OPPOSE the flow of electric current through it is called resistance R, similarly the TERM `(L)/(kA)=R_(H)` is a quantity opposing the flow of heat current can be called as thermal resistance `(R_(H))`. Moreover, mathematical comparison shows that the equation of thermal resistance is similar to that of electrical resistance , `R=rhol/A=l/(sigmaA)""` (Here `rho` is resistivity and `sigma` is conductivity) The equation of equivalent thermal resistance for series and parallel combination of heat conductors are similar to the equations of series and parallel combination of electric resistances. Substances, which are good conductors of electricity, are also good conductors of heat. |
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