A number of spherical drops of liquid, each of radius r, coalesce to form one large drop of radius R and volume V. If T is the surface tension of the liquid, the energy change is:
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Question

A number of spherical drops of liquid, each of radius r, coalesce to form one large drop of radius R and volume V. If T is the surface tension of the liquid, the energy change is:

G1 Physics · Accepted Answer

Step 1: Let the number of small drops be N. Conservation of volume: N(4πr³/3) = V = 4πR³/3. Step 2: Initial surface area Aᵢ = N4πr² = 3V/r. Step 3: Final surface area A𝒇 = 4πR² = 3V/R. Step 4: Released surface energy = T(Aᵢ − A𝒇) = 3VT(1/r − 1/R). Step 5: Since R > r, the expression is positive, so energy is released. Final answer: 3VT(1/r − 1/R) released (Option C).