1. A drop of oil of volume 10-10 m spreads out on water to

make a circular film of radius 10 m. what is the thickness

of the film?

318.3 nm

Explanation:

We approximate the circular film as a cylinder of height h and radius, r. Its volume V = πr²h. Since this volume equals the volume of the oil drop, the height of the circular film is thus h = V/πr²

V = 10⁻¹⁰ m³ and r = 10 m

Substituting into h, we have

h = 10⁻¹⁰ m³/π (10) ²

= 0.3183 * 10⁻¹² m

= 3183 * 10⁻⁹ m

= 318.3 nm