AIIMS2019Physics-Surface Tension

AIIMS 2019 Physics Energy and Surface Tension MCQ Question

Type: MCQ-numerical-Medium-Class 11

A mercury drop of radius 1 cm is sprayed into 10⁶ drops of equal size. The energy expressed in joule is (surface tension of mercury is 460×10⁻³ N/m)

A

0.057

B

5.7

C

5.7×10⁻⁴

D

5.7×10⁻⁶

Correct Answer

Option A

Detailed Explanation

When a mercury drop of radius 1 cm is divided into 10610^6 smaller drops, the radius of each smaller drop becomes r = \frac{1 \, \text{cm}}{10^6^{1/3}} \approx 0.001 \, \text{cm}. The energy associated with the surface tension can be calculated using the formula E=ΔAγE = \Delta A \cdot \gamma, where ΔA\Delta A is the change in surface area and γ\gamma is the surface tension. The initial surface area of the larger drop is Ainitial=4πR2A_{\text{initial}} = 4\pi R^2 and the total surface area of the smaller drops is Afinal=1064πr2A_{\text{final}} = 10^6 \cdot 4\pi r^2. Calculating the energy change yields approximately 0.057J0.057 \, \text{J}, making option A correct. The other options are incorrect as they either underestimate or overestimate the energy change based on incorrect calculations of the surface area or the surface tension.

Found an issue with this question?