Solar constant is estimated to be approximately _____ $\mathrm{kJ}$ per second per square meter or _____ $\mathrm{kW}$ per square meter.

The sun rays are allowed to fall on a lens of diameter $20 \mathrm{cm}$. They are then brought to focus on a calorimeter containing $20 \mathrm{g}$ of ice. If the absorption by the lens is negligible, the time required to melt all the ice is

(Solar constant $=1.9 \mathrm{cal} {\min }^{-1} {\mathrm{cm}}^{-2}$ and $L=80 \mathrm{cal} {\mathrm{g}}^{-1}$)