Earth receives `1400 W//m^2` of solar power. If all the solar energy falling on a lens of area `0.2m^2` is focused on to a block of ice of mass 280 grams, the time taken to melt the ice will be….. Minutes. (`Latent heat of fusion of ice`=`3.3xx10^5J//kg`.)

Answer

5.5

Explanation

Heat required to melt the block `=(0.28kg)(3.3xx10^(5)J//kg)=9.24xx10^(4)J`
Heat received per second `=(1400J//m^(2))(0.2m^(2))=280J`
`therefore`Time taken (in minutes) `=(9.24xx10^(4))/(280xx60)=5.5`