Earth recieves `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.)`

Explanation

`Solar power received by earth =1400W//m^2`
Solar power received by `0.2m^2` area
`=(1400W//m^2)(0.2m^2)=280W`
Mass of ice=280g=0.280kg`
Heat required to melt ice
`=(0.280)(3.3xx10^5)=9.24xx10^4J`
If t is the time taken for the ice to melt, we will have
`(280)t=9.24xx10^4J [:'P=F/t]`
`t=(9.24xx10^4)/280s=330s-=5.5 min`