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Physics - Heat & Thermo Question with Solution | TestHub

PhysicsHeat & ThermoHeat TransferHard2 min

PhysicsHardnumerical

A solid iron sphere ( $ρ = 7800$ kg m⁻³, $c = 450$ J kg⁻¹ K⁻¹) of radius 4 cm at 400 K hangs in a chamber with walls near 0 K. Treat it as a black body. Find the time for it to cool to 200 K, in hours.

Answer:

8.40

Solution:

$t = \frac{r ρ c}{9 σ} (\frac{1}{T _{2}^{3}} - \frac{1}{T _{1}^{3}}) = \frac{0.04 \times 7800 \times 450}{9 \times 5.67 \times 1 0 ^{- 8}} (\frac{1}{20 0 ^{3}} - \frac{1}{40 0 ^{3}}) = 3.009 \times 1 0^{4}$ s = $8.4$ h.

Subject:PhysicsTopic:Heat & ThermoSubtopic:Heat Transfer

⏱ 2m

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