Rays from the sun ar focuseed by a lens of diameter 5 cm on to a block of ice and 10 g of ice is melted in 20 min. Therefore the heat from the sun reaching the earth per min per square centrimetre is
(Latent heat of ice `L = 80 cal g^(-1)`)

Options

A. 2.04 cal `cm^(-2) "min"^(-1)`
B. 0.51 cal `cm^(-2) "min"^(-1)`
C. 4.08 cal `cm^(-2) "min"^(-1)`
D. 3.02 cal `cm^(-2) "min"^(-1)`

Answer

A

Explanation

Heat received to melt 10g of ice `=10 xx 80 = 800` cal Heat received per unit area per min
`= (800)/(pi xx (25)/(4) xx20) = "cal" cm^(-2) "min"^(-1) = 2.04 "cal" cm^(-2) "min"^(-1)`