IIT JEE , AIEEE Forum - Physics , Thermal Physics

gopi_mith

respected sir

please explain the analogy between heat transfer and current transfer

edison

There is one to one analogy between heat and current as explained below.

1) Heat transfer (H) takes place from a system A at temperature T_A, to system B at temperature T_B, as there is a temperature gradient (T_B - T_A). Similarly Current (I) flows from a point A to B if there is a potential gradient i.e. potential difference say (V_B - V_A).

2) Heat flow/transfer takes place until the temperature of the two systems is equal i.e. thermal equilibrium is reached, whereas current flows until there is zero potential difference.

3) H is proportional to (T_B - T_A), and I is proportional to (V_B - V_A)

4) If there is a rod with AB of length 'L' with cross sectional area 'S' and temperature gradient of (T_B - T_A) between the ends and thermal conductivity being 'K' then

5) H = KS (T_B - T_A)/L which is a famous heat transfer equation. Similarly

I =

S (V_B - V_A) / L, where

is electrical conductivity.

6) Further, there is a nice analogy between heat transfer equation and the familiar Ohm's law for electric current. Electric current is charge flow per unit time and is driven by voltage difference. Analogously, heat current H is energy flow per unit time and is driven by temperature difference. We can express R_H = L/KS as thermal resistance, then H = (T_B - T_A)/R_H which is Analogous to ohm's law which is I = (V_B - V_A)/R, where R is electrical resistance.

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