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It takes 20 minutes to melt 10 g of ice,...

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

A

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

B

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

C

`R= 0.204 cal//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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