Q. A single drop of water with radius is formed from coalesce of many identical little droplets of radius having serface tension . The rise in temperature in this process is given by where is the mechanical equivalent of heat and is density of water.
Find .

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A

B

C

D

Solution:

Let there be small drops each of radius which coalesce to form a single drop of radius .
Then

Initial surface area of the 'n' small drops

Final surface area of the big drop formed
Decrease in surface area,

Due to surface tension of the liquid, decrease in area of the liquid surface results in the release of
energy.
The energy released,

If the energy released gets converted into heat, then heat produced,

Let be the rise in temperature of the drop.
mass specific heat rise in temperature

For water

From equations and ,

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