Question

A water drop of diameter 2 cm is broken into 64 equal droplets. The surface tension of water is 0.075 N/m. In this process the gain in surface energy will be

• A. 2.8 × 10-4 J
• B. 1.5 × 10-3 J
• C. 1.9 × 10-4 J
• D. 9.4 × 10-5 J

Answer 1

Answer: (A)

2.8 × 10-4 J

Answer 2

The correct answer is (A) : 2.8 × 10–4 J
$r′ = \frac{r}{4}$
⇒ Δ E = T(Δ S)
= T × 4π(nr ′2 – r 2), n = 64
= T × 4π × (4 – 1)r 2
⇒ Δ E = 0.075 × 4 × 3.142 (3) × 10–4 J
= 2.8 × 10–4 J