Answer:
B. 120 W
Step-by-step explanation:
To calculate the net amount of heat this person could radiate per second, you can use the Stefan-Boltzmann law for radiative heat transfer:
\[ \text{Heat Radiated per second} = \text{Stefan-Boltzmann Constant} \times \text{Surface Area} \times \text{Emissivity} \times \left( \text{Skin Temperature}^4 - \text{Room Temperature}^4 \right) \]
Given values:
- Stefan-Boltzmann Constant (\(\sigma\)) ≈ \(5.67 \times 10^{-8}\) W/(m²·K⁴)
- Surface Area (\(A\)) ≈ 2 m²
- Emissivity (\(e\)) is typically around 0.60 for human skin
- Skin Temperature (\(T_{\text{skin}}\)) = 30°C + 273.15 = 303.15 K
- Room Temperature (\(T_{\text{room}}\)) = 18°C + 273.15 = 291.15 K
Now, plug in the values:
\[ \text{Heat Radiated per second} = 5.67 \times 10^{-8} \, \text{W/(m²·K⁴)} \times 2 \, \text{m²} \times 0.60 \times \left( 303.15 \, \text{K}^4 - 291.15 \, \text{K}^4 \right) \]
\[ \text{Heat Radiated per second} \approx 123.55 \, \text{W} \]
So, the net amount of heat this person could radiate per second into a room at 18°C is approximately 123.55 W. The closest answer choice is B: 120 W.