1.

A number of tiny drops of water all of the same radius r cm combine to form a single drop of radius R cm. The rise in temperature of water is given by (if sigma = S.T. specific heat= 1 cal/g) :

Answer»

`(sigma)/J(1/r-1/R)`
`(3sigma)/J(1/r-1/R)`
`(3sigma)/J(1/(r^(2))-1/(R^(2)))`
`(sigma)/J(1/(r^(2))-1/(R^(2)))`

Solution :Here Energy RELEASED =`4pi(nr^(2)-R^(2)).sigma`
`therefore` Heat PRODUCED=`W/J=(4sigmapi)/J(nr^(2)-R^(2))`
Heat produced in drop=`4/3piR^(3)xx1xxtheta`
`therefore(4sigmapi)/J(nr^(2)-R^(2))=4/3piR^(3)theta`
or `theta=(3sigma)/J(1/r-1/R)`
`therefore` Correct CHOICE is (b).


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