Question

What is the correct formula for the rate of heat transfer (q) through a plane wall of

thickness l and surface are A, when temperature difference between two surfaces is ΔT ?

The thermal conductivity is k.

a. q = (k A ΔT) / l

b. q = k A l ΔT

c. q = (ΔT) / (k A l)

d. none of the abovet
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Answer 1

THERMAL CURRENT FORMULA:

• Let temperature difference between the two surfaces be ∆T.

• 'k' is conductivity coefficient, 'A' is the cross-sectional area. 'l' is the length of the conductor.

Now, the correct expression is :

$q = \dfrac{temperature \: difference}{resistance}$

$\implies q = \dfrac{\Delta T}{ \bigg( \dfrac{l}{kA} \bigg)}$

$\boxed{ \implies q = \dfrac{kA\Delta T}{ l} }$

Option a) is correct ✔️.