NEET (UG) 2024 — Question 28

The excess force required to overcome surface tension is the force along the circumference of the disc. Formula: $F = T \times 2\pi R$. Given: $T = 0.07\,\mathrm{N\,m^{-1}}$, $R = 4.5\,\mathrm{cm} = 0.045\,\mathrm{m}$. Substitute: $F = 0.07 \times 2 \times 3.14 \times 0.045$. Calculate: $2 \times 3.14 \times 0.045 = 0.2826$, then $0.07 \times 0.2826 = 0.019782\,\mathrm{N}$. Convert to mN: $0.019782\,\mathrm{N} = 19.782\,\mathrm{mN} \approx 19.8\,\mathrm{mN}$. Thus the required excess force is $19.8\,\mathrm{mN}$.