Q: When a big drop of water is formed from n small drops of water, the energy loss is 3 E , where E is the energy of the bigger drop. If R is the radius of the bigger drop and r is the radius of the smaller drop, then number of smaller drops (n) is

Sol: The energy of n small drops – the energy of the bigger drop = Energy loss by bigger drop

n × 4 π r^{2} × T – 4 π R^{2} × T = 3 × 4 π R^{2} × T

n × 4 π r^{2} = 12 π R^{2} + 4 π R^{2}

⇒ n = 4 R^{2}/r^{2}