Question

Calculate the diameter of a water drop if the excess pressure inside the drop is 80 N/m². (Surface Tension of water = 7.2 × 10⁻² N/m).

Answer 1

Given: Surface tension (T) = 7.2 × 10⁻² N/m

Excess pressure = (P_i − P₀) = 80 N/m²

To find: Diameter of water droplet = ?

Formula: `P_i - P_0 = (2T)/r`

∴ `r = (2T)/((P_i - P_0))`

= `(2 xx 7.2 xx 10^-2)/80`

= `(2 xx 72 xx 10^(-3))/(80)`

= `(144 xx 10^(-3))/(80)`

= 1.8 × 10⁻³ m

= 1.8 mm

∴ Diameter (d) = 2 r

= 2 × 1.8

= 3.6 mm