First slide

Radiation

Question

A black body of surface area 10 cm² is heated to 127°C and is suspended in a room at temperature 27°C. The rate of loss of heat is

Easy

A

1 W
B

2 W
C

3 W
D

4 W

Solution

Applying Stefan's law, we have
$\begin{array}{l} \frac{dE}{dt} = σA (T_{1}^{4} - T_{0}^{4}) \\ = (5 \cdot 67 \times 10^{- 8}) \times (10 \times 10^{- 4}) [(400)^{4} - (300)^{4}] \\ = 1 watt. \end{array}$

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