Question

Each minute earth receives about $2$ calorie of heat energy per square centimetre from the sun. This constant is called solar constant $S$ . Express solar constant in $SI$ units.

• A. 8 kW/m²
• B. 1.4 kW/m²
• C. 1.8 kW/m²
• D. 2.5 kW/m²

Answer 1

Answer: (B)

Given that
S = 2 cal/cm²/min
But as 1 cal = 4.18 J, 1cm = 10^-2 m and 1 min = 60 s
$\text{S}=\frac{2\times \text{4.18 J}}{{\left({\left(\text{10}\right)}^{-2}\text{m}\right)}^2\left(\text{60s}\right)}$
$\approx \text{1.4}\times {\text{10}}^3\frac{\text{J}}{{\text{m}}^2\text{s}}\text{or}\text{S}=\text{1.4}{\text{kW/m}}^2$