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}$