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Fourier's law of heat conduction (1D) states:
A{'text': '$q = kAT$', 'label': 'A'}
B{'text': '$q = -kA\\frac{dT}{dx}$ — heat flow rate is proportional to negative of temperature gradient times area', 'label': 'B'}
C{'text': '$q = h(T_s - T_\\infty)$', 'label': 'C'}
D{'text': '$q = \\sigma T^4$', 'label': 'D'}
Answer & Solution
Correct answer: B. {'text': '$q = -kA\\frac{dT}{dx}$ — heat flow rate is proportional to negative of temperature gradient times area', 'label': 'B'}
Fourier's law: q = −kA·dT/dx. The negative sign means heat flows from hot to cold (down the gradient). k is thermal conductivity (W/m·K). Heat flux (per area) = q'' = q/A = −k·dT/dx (W/m²).
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