Question

8000 identical water drops are combined to form a bigdrop. Then the ratio of the final surface energy to the initial surface energy of all the drops together is 

(A) 1 : 10 

(B) 1 : 15 

(C) 1 : 20 

(D) 1 : 25

Answer 1

Correct option: (C) 1: 20

Explanation:

As mass is constant R³ = nr³ 

R³ = 8000r³ 

R = 20r         i.e. (R/r) = 20

[{surface energy of single drop (radius R)}/ {surface energy of all 8000 drops (radius r)}]

= {4πR²T / (4πr²T × 8000)}

= {R² / (r² × 8000)}

= (20² / 8000) = (400 / 8000) = (1 / 20)

∴ ratio = 1 : 20