JEE Challenger
More from Mechanical Properties of Fluids

Surface Energy of Detached Liquid Drop

After the drop detaches, its surface energy is

Options

A

1.4×10−6 J1.4\times 10^{-6}\text{ J}

B

2.7×10−6 J2.7\times 10^{-6}\text{ J}

Correct
C

5.4×10−6 J5.4\times 10^{-6}\text{ J}

D

8.1×10−6 J8.1\times 10^{-6}\text{ J}

Step-by-Step Solution

To find the surface energy of the detached liquid drop, we consider it to be spherical once detached from the dropper.

From the previous problem, the radius of the detached drop is:
R≈1.4×10−3 mR \approx 1.4 \times 10^{-3}\text{ m}

The total surface area AA of the spherical drop is given by:
A=4πR2A = 4\pi R^2

Substituting the radius RR:
A=4π(1.4×10−3 m)2=4π×1.96×10−6 m2≈2.463×10−5 m2A = 4\pi (1.4 \times 10^{-3}\text{ m})^2 = 4\pi \times 1.96 \times 10^{-6}\text{ m}^2 \approx 2.463 \times 10^{-5}\text{ m}^2

The surface energy UU of the drop is the product of the surface tension TT and the surface area AA:
U=T⋅AU = T \cdot A

Given the surface tension T=0.11 N m−1T = 0.11\text{ N m}^{-1}:
U=0.11×2.463×10−5 J≈2.71×10−6 J≈2.7×10−6 JU = 0.11 \times 2.463 \times 10^{-5}\text{ J} \approx 2.71 \times 10^{-6}\text{ J} \approx 2.7 \times 10^{-6}\text{ J}

Therefore, the correct option is B.