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It takes 20min to melt 10g of ice, when ...

It takes 20min to melt 10g of ice, when ray from the sun are focussed by a lens of diameter 5cm on to a block of ice. Calculate the heat received from the sun by `1^(2)//`min (Given L= 80kcal/kg)

A

R= 2.04cal/`cm^(2)`-min

B

R= 3.04 cal/`cm^(2)`-min

C

R= 0.204cal/`cm^(2)`-min

D

R=2.4 cal/`cm^(2)`-min

Text Solution

Verified by Experts

The correct Answer is:
A
Let R= rate at which heat is received.
`Q_(1)= R xx A xx t`
`= R xx pi (2.5)^(2) xx (20 "min")`
=392.5R cal
Heat required to melt the 10g of ice `Q_(2)= mL = 80 xx 10=800` cal
392.5R= 800
`R= (800)/(392.5)= 2.04` cal/`cm^(2)`-min
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