Question

i) When number of droplets coalesces and form a drop, state whether
the surface area decreases or increases ?​

Answer 1

Answer:

Answer

Let n be the number of little droplets Since volume will remain constant hence volume of n little droplets = volume of single drop

∴             n×34​πr3=34​πR3       or         nr3=R3

Decrease in surface area = n x 4πr2−4πR2

or                  ΔA=4π[nr2−R2]=4π[rnr3​−R2]=4π[rR3​−R2]=4πR3[r1​−R1​]

Energy evolved W = T x decrease in surface are                     =T x 4πR3[r1​−R1​]

Heat produced, Q=JW​=J4πTR3​[r1​−R1​]                       But Q=msdθ

where m is the mass of big drop s is the specific heat of water and dθ is the rise in temperature

∴              J4πTR3​[r1​−R1​]= volume of big drop x density of water x sp. heat of water x de

or,             34​πR3×1×1×dθ=J4πTR3​(r1​−R1​) or,          dθ=J3T​[r1​−R1​]

Explanation: